Metal-Working Machines

Modified on 2012/02/06 20:49 by Joel Havens Categorized as Metalworking Machinery
&nbsp &nbsp &nbsp All the work performed upon metals for the purpose of fashioning them into tools, implements, and appliances of various kinds is effected either by cutting, abrading (including polishing), or bending, to which processes those of stamping, flanging, and punching are related in various degrees. All these mechanical operations, more particularly those of bending, punching, and stamping, are dependent on the property possessed by all solids, and especially by metals, of spreading under pressure, and in many cases the line of demarcation between one process and another is very difficult to trace. Thus in some machines the process of cutting frequently shades off into that of abrasion and the process of stamping into that of bending. {br}
&nbsp &nbsp &nbsp The term "machine-tools" has by common consent been adopted to designate those machines which are employed in working iron by purely mechanical operations. They supplant metal-working hand-tools, just as wood-working machinery supplants wood-working hand-tools; but, while wood-working machines are to be considered as machine-tools no less than those for working metal, the usage of the trade has made and maintained the distinction between machine-tools and wood-working machinery. {br}

<h1>Classification</h1>{br}
# <i>Lathes</i>: axle, bolt, car-wheel, driving-wheel, die-grinding, engine, forming, gun-stock, gun-hoop, hand, pattern-makers', pulley, rod, spinning, shafting, screw-cutting, turret
# <i>Planers</i>: connecting-rod, crank, friction, frog and switch, open-side, pit, plate, regular, rotary, valve-seat (rotary), valve-seat (reciprocating)
# <i>Shapers</i>: crank, cylinder, double, geared, pillar, single, traversing
# <i>Slotters</i>: locomotive-frame, regular, screw, understroke
# <i>Boring-mills</i>: box (horizontal), box (vertical), chord, car-box, car-wheel, crank-pin, cylinder, hand-wheel, horizontal, link, pulley, tire, vertical
# <i>Drilling-machines</i>: arch-bar, automatic, cotter, horizontal, key-seat, multiple, portable, radial, rail, sensitive, turnbuckle, universal, vertical
# <i>Shears</i>: angle, bar, circular, plate
# <i>Milling-machines</i>: bolt-head, column, double, horizontal, key-seat, regular, steam-chest seat, universal, vertical
# <i>Grinding-machines</i>: cutter, lathe-centre, plain, reamer, surface, twist-drill, tool, universal
# <i>Bolt-machines</i>: cutting, heading, head-milling, threading, turning
# <i>Nut-machines</i>: chamfering, facing, milling, punching, tapping
# <i>Presses</i>: crank-pin, cutting, drop, drawing, geared, hydraulic, stamping, wheel
# <i>Miscellaneous Machines</i>: belt-polishing, centering, crank-pin turning, cutting-off, cross-head-pin turning, chucking, die-sinking, facing, forging and upsetting, gear-cutting, grooving, heading, marking, measuring, punching, platebending, profiling, rack-cutting, rail-bending, shaft-straightening, screw-making, quartering, rail-cutting, riveting (steam), riveting (hydraulic), riveting (pneumatic), tool-grinding, wheel-turning, wheel-quartering; and steam-hammers. {br}
&nbsp &nbsp &nbsp It will be noted that there is a marked tendency toward specialization. Under each head there are built for particular classes of work other forms than those above mentioned, but, not being in general use, they are not specified. Some of those named under "Miscellaneous" might, indeed, be classed under "Lathes," "Milling-machines," etc. The present section will include a review of typical machines in each of the more important classes. {br}

<h1>Sharpening, Grinding, and Abrading Devices</h1> {br} &nbsp &nbsp &nbsp To reduce the size, vary the shape, or improve the surface of metals there may be employed abrading devices, such as the file and rasp, the hone, whetstone and grindstone, the emery-wheel, and the corundum-wheel. The character of work done by these in removing material by a gnawing action merges so closely into the work done by rotating cutters in the so-called "milling"-machine that, as regards results, each one must be considered in comparison with all the others. But the milling-machine (and, indeed, the grinding-machine) is now an instrument of precision and worthy of being ranked with machine tools. We shall first consider the file and the rasp, or primitive hand-tools, and secondly the hone and the grindstone because they are used to sharpen edge-tools, and shall incidentally treat the grindstone as a shaping device as well as an appliance for sharpening. {br}

<h4>Files and Rasps</h4>
[imageauto|Files and Rasps|{UP}/Metal-Working Machines/PL 19 Fig 1 and 2.jpg]{br}
&nbsp &nbsp &nbsp The most common abrading tools are the file and the rasp, the former being used for metal and the latter for wood, horn, and other fibrous materials. These tools, especially the file, exist in almost endless variety in length, contour, thickness, and style and fineness of cut. The file and the rasp, like the grindstone and the emery-wheel, are used to remove projections and rough portions from metallic objects in order to bring them to a desired smoothness of surface and to required dimensions. The emery- and corundum-wheels and the grindstone may be regarded as rotary files driven by power. It is not deemed advisable to give here an itemized description of all the varieties and types of rasps and files, as it would be but a mere catalogue of no special interest. Figs. 1 and 2 represent various types of files.{br}

<h4>Vises</h4>
[imageauto|Vises|{UP}/Metal-Working Machines/PL 19 Fig 3 and 4.jpg]{br}
&nbsp &nbsp &nbsp To aid in properly holding objects which are being filed and ground there are employed various kinds of vises, both hand and bench (Figs. 3, 4). The bench-vise is so called because it is fastened to the workbench. Bench-vises are of two general classes, (1) those having a hinge, and (2) those with a parallel movement; the jaws are moved and held either by a screw or by a ratchet and clamping device. For filing and grinding these vises are generally of cast iron; for chipping they are principally of wrought iron.{br}

<h4>Sharpening</h4> &nbsp &nbsp &nbsp For sharpening small tools, such as knives, chisels, etc., there is used a stationary hone or oil-stone having a flIat abrasive surface, over which is moved the material to be ground. Gouges have their concave edges worked by slip-stones having preferably concave edges of the same radius of curvature as the cutting-edge of the tool.{br}

<h1>Grinding</h1> {br} &nbsp &nbsp &nbsp Where the article to be ground is large, as in the case of a scythe, a paper-cutter blade, a planer-knife, a saw-blade in process of manufacture, or a casting having its skin and sprues worked off, it is best to have the stone in the form of a disc, which, according to the size of the piece to be worked, may be revolved by hand-power, a foot-treadle, or a belt.{br}

<h4>The Grindstone</h4>
[imageauto|Grindstone|{UP}/Metal-Working Machines/PL 19 Fig 7.jpg]{br}
&nbsp &nbsp &nbsp Perhaps the stones of grinding-mills, as in revolving they wore each other away, suggested the use of the grindstone, which is one of the oldest tools used for changing the shape of metallic objects. It acts in the removal of numberless small particles, and is employed not only to change an original shape and outline, but also to give a polish. It is mounted upon a shaft, which passes through a square hole in the stone, and which was originally carried in boxes on a wooden frame, for which subsequently an iron frame was substituted. At present the stones, particularly if large, are held in place on the arbor by and between cast-iron flanges, which are slightly concave on their inner sides. Such stones run from 1 inch to 6 feet in diameter and from ¼ of an inch to 18 inches face. Most of the grindstones used in the United States come from Yorkshire, England. There are known and used many varieties of grit, which differ in the size and sharpness of the grains and the hardness of the matrix by which they are held together. The simplest form of grindstone was mounted in a very crude wooden frame, and was kept wet by a drip from a keg or a can suspended above the stone. Subsequently the stone was revolved in a movable trough filled with water. The trough and the frame are now generally made of cast iron in one piece, while the mounting is so improved that the arbor runs on anti-friction rollers. Figure 7 shows an ordinary grindstone-mounting. One excellent form of portable grindstone-frame is made in a solid casting of box form with two divisions, one for the water in which the stone turns and the other for clean water for cleansing tools. There is an outlet for the discharge of the deposit and a steady rest for grinding small tools. The grindstone, however, is being very generally superseded by the emery- and corundumwheels, whose advantages are that their particles are naturally harder, their cutting-edges are not water-worn as with sandstone, the grains in any one wheel are all of a size, the softness of the matrix may be chosen to suit the work to be done, and, furthermore, they may be produced at very reasonable rates in an almost infinite variety of size and of profile.{br}

<h4>Emery-wheels</h4>
[imageauto|Emery Wheel|{UP}/Metal-Working Machines/PL 19 Fig 8.jpg]{br}
&nbsp &nbsp &nbsp These wheels (Fig. 8), which are practically artificial grindstones, are used to supplement the lathe and the planer in producing true cylindrical or plane surfaces. There has never been made a lathe that will turn truly round, nor a planer that will plane truly flat. In the latter respect the emerywheel produces work of a trueness and finish which equals the best produced by the more expensive method of scraping and fitting upon planes, and which cannot be produced by lathe and hand-work. Emery-wheels are now very largely used for grinding the treads of "chilled" car-wheels. For the production of perfectly cylindrical surfaces, as for car-brasses, an emery-wheel with semicircular convex rim does excellent work at a very rapid rate. The brasses are fed along under the machine, which, if they are well moulded, will grind them at the rate of one per minute from the rough to a correct fit, leaving them with a fine finish. An emery-wheel to be of maximum service should be safe from bursting, should cut freely with but little heat, should be reasonably durable, as far as possible should be free from noxious dust and from unpleasant smell, should be of even density, should be of perfect profile, and should wear evenly. It should be well mounted and properly run, should be run at its most efficient speed as determined by practice and recommended by its maker, and should not have the work forced up against it too hard. No emery-wheel will run well if allowed to jump. A good rim-speed is about 5500 feet per minute. As a rule, an emery-wheel will remove in the same number of hours from twelve to fifteen times as much metal as a file. Emery-wheels are "turned" by a diamond-pointed tool consisting of a crystal of boart or black diamond firmly set in the end of a steel rod and furnished with a suitable wooden handle, or the boart may be mounted in a square rod and used as a lathe-tool. {br}
&nbsp &nbsp &nbsp One of the best-known manufacturers of emery-wheels classifies them according to their coarseness of grain and hardness.{br}<i>Class one</i>, which is coarse and hard, is suitable for edging cast iron or steel, for taking gates and sprues from castings, and for general rough grinding.{br}<i>Class two</i>, which is of medium coarseness and is hard, is about the same as class one, but may also be used to excellent advantage for chipping, moulding-knives, and lathe-tools, and for gumming saws. {br}<i>Class three</i>, medium grain and soft, is suitable for grinding brass and for surface-work on steel and on cast and wrought iron. If used for edging, it will cut fast and freely, and will also wear away rapidly. {br}<i>Class four</i>, which is hard and of medium coarseness of grain, is for grinding not only upon light work, but also upon all work which will not affect the shape of the wheel. {br}<i>Class five</i> is used for grinding upon brass or other soft metals, for polishing fine surfacework on iron and steel, and for sharpening tools. An extra class, good for "gumming" saws, is moderately coarse, soft and of open texture, and grinds freely, while it generates but little heat. The ordinary emerywheel frame, which so effectually supplanted the grindstone in most of its uses, has in the performance of good work been superseded by the universal grinding machine.{br}

<h4>The Universal Grinding-machine</h4>
[imageauto|Universal Grinding-machine|{UP}/Metal-Working Machines/PL 19 Fig 9.jpg]{br}
&nbsp &nbsp &nbsp This machine (Fig. 9) has importantly modified machine-shop practice, as by grinding it readily gives an accuracy in finish previously considered commercially impracticable, and, moreover, demonstrates that most conical and cylindrical surfaces, soft or hard, can be better and more economically finished by grinding than by any other process. In many kinds of work it takes the place of a lathe, which it supplements by finishing other work previously roughed out. It does both internal and external grinding, straight or taper, and finishes spindles, arbors, either straight or angular cutters, reamers, jewellers' rolls, hardened boxes, and standard plugs and rings. The sliding table (A) rests upon the bed (B) and carries the swivel-table (C). Thus, for grind ing tapers, the line of centres of the head- and foot-stock can be set at any angle with the sliding table without throwing the head-and-foot stockspindle out of line. The table (C) is provided with an adjusting screw (D) and a scale showing the taper both in degrees and in inches per foot. The wheel-bed (E) is mounted upon a knee (not shown in illustration), and may be set at any angle from 0° to 90° on either side of the line at right angles with the sliding table. The semi-circumference at the lower edge of the wheel-bed is graduated in degrees. The wheel-slide rests on the wheel-bed. The table may be fed and reversed automatically or by hand. The cross-feed is operated by hand. The head-stock (F) is attached to a base-plate (G) bolted to the swivel-table (C), and is made to swivel about a centre-pin. The circumference of the swivel-table at its lower edge is graduated to degrees. A friction-brake enables the driving-drum to be stopped almost instantly. The swivel-table can be moved to either side of its central position to grind tapers from o to 2 inches per foot and from 0° to 10° in angular measurement. For grinding work on the faceplate or chuck the head-stock can be set at any angle within the whole circle. Work can be revolved upon dead centres or upon one dead and one live centre. Two tapers can be ground, either external or internal, without changing any of the settings. Ample provision is made for wet grinding.{br}

<h1>Metalworking Lathes </h1>{br}
<h4>Lathe Tools</h4>
[imageauto|Lathe Tools|{UP}/Metal-Working Machines/PL 19 Fig 5 and 6.jpg]{br}
&nbsp &nbsp &nbspReferring to Figs. 5, 6, number 1 is known as a "left-side" tool; number 2 is the same style, made "right hand." Numbers 3 and 4 are the same types, '' bent'' for working at an obtuse angle. Number 5 is a heavy "diamond-point" tool for cast iron; numbers 6 and 7 are right-hand and left-hand diamond points for steel and wrought iron. Number 8 shows a "half-diamond point" and number 9 a "round-nose." Number 10 is a "water-finishing" tool, which takes off a very fine, wide turning. Number 11 is for cutting off pieces in the lathe; number 12 for roughing stock; number 13 for cutting external or "male" V-threads, and number 14 the same as number 13, bent. Number 15 is for turning a hollow cylinder; number 16 for cutting an internal or "female" screw-thread. All the foregoing are used in a slide-rest. {br}

[imageauto|Lathe Tools|{UP}/Metal-Working Machines/PL 20 Fig 4 and 8.jpg]{br}
&nbsp &nbsp &nbsp Of Figures 4 to 8 , Figures 5 and 6 are ordinary turning-tools for metal and Figure 4 one for wood, while Figures 7 and 8 are examples of a tool whose cutting-edge consists of a three-cornered bar or piece of steel set in an iron stock. This allows of very economical use of the steel and dispenses with the otherwise unavoidable forging of the entire tool.{br}

<h4>Slide-rest Lathes</h4>
[imageauto|Slide Rest Lathe|{UP}/Metal-Working Machines/PL 20 Fig 10.jpg]{br}
&nbsp &nbsp &nbsp Lathes in which the guidance of the tool is effected by mechanism instead of by hand are called "slide-rest" lathes, a simple form being shown in Figure 10. The mandrel carries a stepped or cone pulley with various diameters corresponding to those of a similar stepped pulley on the counter-shaft, the revolving motion of the latter being transmitted to the former by a belt. The tool is firmly secured to a rest, which receives a motion parallel to the rotating axis by a leadscrew in the interior of the bed, the nut and the screw being carried by the slide-rest. The rotation of this lead-screw is derived from that of the mandrel by belt and wheel-gearing. This arrangement is suitable only for producing cylindrical surfaces.{br}

[imageauto|Curved Slide Rest|{UP}/Metal-Working Machines/PL 20 Fig 13.jpg]{br}
&nbsp &nbsp &nbsp Sometimes engine-lathes are provided with contrivances for guiding the tool in other than a straight line—for instance, with a special guide-bar, against which the uppermost cross-slide is constantly pressed by a weight (curved slide-rest; Fig. 13).{br}

<h4>Double-tool Lathe</h4>
[imageauto|Double Tool Lathe|{UP}/Metal-Working Machines/PL 21 Fig 1.jpg]{br}
 &nbsp &nbsp &nbsp The lathe shown in Figure 1 differs from the preceding in two particulars. Besides the mandrel the head-stock contains an auxiliary appliance placed parallel to the mandrel, so that the former can be connected with the latter by a pair of wheels, through which the motion transmitted to the step-pulleys can be communicated in a retarded velocity to the mandrel itself. As the step-pulleys can be directly connected with the mandrel, it is possible, with the four varying diameters of the step-pulley, to give the work eight different velocities, and thus to obtain the most advantageous peripheral speeds according to the different materials to be worked. This class of appliances is described in very full detail under the head of screw-cutting lathes. {br} &nbsp &nbsp &nbsp Another peculiarity of the lathe (Fig. 1) is the simultaneous action upon both sides of the work of two turning-tools, which, it is claimed, not only double the capacity of the lathe, but also, by the action of the tool, prevent the work from springing.{br}

[imageauto|Lathe Cross Slide Rests|{UP}/Metal-Working Machines/PL 20 Fig 11 and 12.jpg]{br}
 To hold these two tools the carriage has two special cross-slide rests, each allowing its tool to be traversed in two directions at right angles to each other. The details of such slides are shown in Figures 11 and 12. {br}

<h4>Gap-bed Lathe</h4>[imageauto|Gap Bed Lathe|{UP}/Metal-Working Machines/PL 20 Fig 14.jpg]{br}
 &nbsp &nbsp &nbsp To give engine-lathes the widest possible range of work they are frequently provided with a gap-bed (Fig. 14). Directly alongside the head-stock and beneath the head of the mandrel—which must be provided with suitable contrivances for securing the work— the bed-plate is depressed within a certain length, to allow turning work, if not too long, with a radius greater than the height of the centre from the general bed-level. The advantage of this kind of lathe lies in the fact that work is most frequently either long and thin or short and thick. {br}

[imageauto|Face Plate Lathe|{UP}/Metal-Working Machines/PL 21 Fig 2.jpg]{br}
[imageauto|Face Plate Lathe|{UP}/Metal-Working Machines/PL 21 Fig 3.jpg]{br}
&nbsp &nbsp &nbsp This lathe forms the transition to those exclusively intended for spherical or flat work of a larger diameter, the so-called "face-plate" lathes (Figs. 2, 3), in which the work is fastened to a large cast-iron plate (face-plate) provided with hollows and T-shaped slots and screwed upon the head of the spindle. The tail-stock or sliding poppet either is placed, together with the slide-rest, upon a special bed (Fig. 3)—which is, however, connected with the head-stock by a foundation-plate—or is entirely omitted (Fig. 2), in which case only a special framing for the slide-rest is required. Such lathes are very convenient for turning large pulleys, gear-wheels, turbines, etc.{br}

<h4>Wheel-turning Lathe</h4>[imageauto|79" Swing Wheel Lathe|{UP}/Metal-Working Machines/PL 21 Fig 4.jpg]{br}
 &nbsp &nbsp &nbsp The wheel-turning machine (Fig. 4), a variety of the face-plate lathe, is used for turning car- and locomotive-wheel flanges. In turning the axle the wheels and flanges remain upon it, thus forming one piece; and this, by reason of its liability to spring, requires to be driven from both sides. For this purpose each wheel is connected with a face-plate receiving independent although synchronous rotation, whereby all chatter due to the heavy cut is avoided. The slide-rests must be of sufficient height for the tools to work nearly at the height of the axle.{br}

<h4>Copying-lathe</h4>[imageauto|Copying Lathe|{UP}/Metal-Working Machines/PL 20 Fig 9.jpg]{br}
 &nbsp &nbsp &nbsp There is a strong analogy between copying-lathes for metal and those for wood, the latter having, however, higher speed. One peculiar modification of the lathe allows the production of irregularlyshaped articles and copies of a pattern. Part of this so-called "copying-lathe" is shown in Figure 9, and has some relationship to the gauge-lathe referred to under the head of wood-working machinery. The pattern and the work to be shaped like it are secured between chucks by means of a head-stock with two spindles and a double sliding poppet, and are turned at equal speeds and in the same direction. Against the pattern there is constantly pressed a smooth-edged disc attached to the same crossslide with the rotating cutter. This cutter, thus receiving a certain displacement from the axial line depending on the pattern, reproduces on the work, if properly set, the form of the latter. As the rotating cutter replaces, in this case, the ordinary turning-tool, this machine may be classed with milling-machines as well as with lathes. {br}

<h4>The Engine-lathe</h4> [imageauto|Engine Lathe|{UP}/Metal-Working Machines/PL 22 Fig 1.jpg]{br}
 &nbsp &nbsp &nbsp  This machine (Fig. 1) has its power transmitted from the counter-shaft to a cone in the head-stock, which, when disconnected, revolves loose upon the main spindle. If moderate work not requiring much power is to be performed, the cone is connected to the spindle by a small clutch between the large gear on the spindle and the inside edge of the cone. If great power is needed, the clutch is unlocked and the back gearing engaged, which considerably multiplies the power. The "work" is placed between the centres, the tool being held in the tool-post and guided by the several hand-wheels in the apron-carriage and compound slide.
For cutting threads combinations of change-wheels are placed at the end of the live head, to connect the spindle with the screw in such ratio as the index-plate on the lathes shows will be the result. Means are provided in the apron for automatically running the carriage to the right or to the left and for moving the tool in or out, for cross-feeding. The bed of this lathe has a hollow and double centre-rib, which stiffens it, while adding comparatively little weight.{br}

<h4>The Screw-cutting Lathe</h4> [imageauto|62" Screw-Cutting Lathe|{UP}/Metal-Working Machines/PL 22 Fig 2.jpg]{br}
&nbsp &nbsp &nbsp This machine (Fig. 2) is intended for the production of circular work of all kinds in metal up to an extreme diameter of 62 inches, or of 46 inches should it have to rotate over the carriage. The machine consists of a combination of mechanisms, (1) for imparting motion to the work (the live head), (2) for holding and guiding a tool (the carriage), (3) for imparting motion to the tool in given ratio to the motion of the work (the feed), and (4) for supporting the outer end of the work (the dead or poppet head), the whole being supported on a long box-like frame called the bed.{br} 
The live head consists of a framework containing a cone pulley (A) running upon a horizontal shaft or live spindle (B), on the outer end of which is a large circular face-plate {C) provided with slots, to secure work to it by means of bolts. It is necessary, on account of varying sizes of work, to be able to vary the rate of motion of the face-plate; and to secure this end there is used a series of toothed wheels, known as the "head" gearing. The "cone" pulley is made up of five faces of different diameters and is driven by a belt from a similar stepped pulley overhead in which the sequence of sizes is reversed. By the transfer of the belt from one to another of these diameters five changes of motion are obtained. To obtain still other changes there is used a "back" gearing, consisting of a train of four gears, starting from a small gear on the end of the cone pulley, running into a large wheel (D) on the back gear-shaft (E); this latter carries a small gear (F), which in turn meshes with a large gear (G) on the live spindle or into a large gear (H) on the triple-gear shaft.{br}
&nbsp &nbsp &nbsp Five changes are imparted by the "back" gearing and five by the "triple" gearing, thus giving, with the pulleys, fifteen changes to the face-plate motion. The "triple" gearing is effected by the small gear (F) driving the large gear (H), which is on the shaft (J) with the small gear (K), which drives the internal toothed surface of the face-plate (C). When any one of these series is employed, the others must be kept idle or "thrown out of gear." As the spindle always receives the same motion as the face-plate, it is necessary to allow the cone to run freely on it; but the gear (G) is tightly fastened to it and can be locked to the cone pulley, thus imparting the motion of the latter directly to the face-plate. When the "back" gearing is used, the cone is unlocked, and the motion then comes to the spindle and face-plate, as before, through the gear (G), but very much reduced, by reason of the ratios of the gears through which the motion has come. When the "back" gearing is not in use, the gears (D) and (F) are moved lengthwise on the shaft (F), one to the left, the other to the right, thus throwing them out of gear and allowing the cone pulley to be locked again to the gear (G). When the "triple" gearing is in use, the cone pulley is unlocked, the gear (D) is pushed into the small gear, on the end of the cone pulley, and the gear (F) moved until it comes into line with the gear (H). This gear (H) is mounted on the shaft (J) carried in eccentric bearings, which have already been thrown down, so that the small gear (K) engages with the toothed surface of the face-plate. The moving of the gear (F) into line with the gear (H) engages them, thus completing the series or train to the spindle and face-plate. When the" triple" gearing is not in use, the shaft (J) is thrown upward by its eccentric bearings, and so the pinion (K) is out of gear with the face-plate, thus allowing the other gears to be used freely. {br}
&nbsp &nbsp &nbsp The next point is the carriage, which consists of a platform (L), bridging the bed and called the "saddle" of an apron (M), containing the means of obtaining motion of a cross-slide of a swivel-piece and of a tool-slide (P) provided with bolts, to secure the tool. The motion of the tool-slide is effected by a screw worked by the handle (Q), and by rotating the swivel-piece (O) it can be moved at any angle to the faceplate in a horizontal plane. The cross-slide (N) can be moved by a screw, which can be worked either by the handle (R) or by power through the gears inside the apron controlled by the hand-nut (S). Its only motion is parallel to the face-plate. The saddle can be moved along on the bed (only at right angles to the face-plate) in three ways: (1) by hand, with the hand-wheel (W) and appropriate gearing in the apron working into the rack seen on the edge of the bed; (2) by power through a train of gearing driven by a groove cut in the lead-screw (X) and working the rack on the side of the bed, being controlled by the hand-nut T (both this powerfeed and that on the cross-slide can be reversed or stopped by moving the lever (U) to one side or the other or stopping it in the middle); and (3) by closing a segmented nut (made in two pieces) upon the thread of the lead-screw (X) by means of the handle (V). {br}
&nbsp &nbsp &nbsp The feed is driven from the back end of the live spindle by the gear (1) working into the gear (2) on the shaft (3) carrying three gears keyed fast, as shown. On a shaft (4) below these and meshing with them are three loose gears, any one of which can be fastened to the shaft by a sliding key operated by a clutch-pin (5). On the other end of the shaft is a gear which imparts motion to the lead-screw (X) through an appropriate train of gears, and thence to the carriage.{br}
&nbsp &nbsp &nbsp The dead or poppet head consists of a spindle (10), of a top piece (11), and of a base piece (12), the whole being firmly clamped to the bed by means of bolts (13). It is necessary for the spindle (10) to have a lengthwise motion; and this is imparted by a screw operated by a handwheel (14) and a pair of gears (15). The whole head can be moved along on the bed by a pinion gearing into the rack on the side of the bed and operated by the ratchet-lever (16). The top piece (11) can be moved transversely across the bottom piece (12), thus throwing one end of the work nearer the tool than the other and thereby producing conical surfaces. Both spindles (in each head) have inserted in their ends pointed pieces, called "centres," upon which the work is supported.{br}
&nbsp &nbsp &nbsp When work is slight or cannot be reached by the dead centre or is very long, it is customary to use what is known as a "steady-rest." This consists of a base piece (20), which can be firmly clamped to the bed, of a top piece (21), and of three steel pieces (22), called "jaws." These pieces, which are adjustable, can be moved by screws until they touch the work, and can then be clamped; they then provide a bearing which supports and steadies the work. To get the work in and out of this conveniently the top piece (21) is made separate and can be entirely removed, thus allowing ample room for handling. It will be seen that this machine provides a variety of speeds of rotation of the work, a variety of rates of power-feed to the tool, supports for the steady running of the work, and movements to the tool by means of which true cylindrical, angular, or flat surfaces may be produced.{br}

<h4>Turret Screw-cutting Lathe</h4> [imageauto|Screw-Cutting Lathe|{UP}/Metal-Working Machines/PL 22 Fig 3.jpg]{br}
&nbsp &nbsp &nbsp  Of screw-machines one of the best is represented in Figure 3, which is a lathe having a hollow spindle with a chuck on each end, a carriage having hand and power movement and carrying two tools and a set of open screw-cutting dies, and a slidetool block having four variations of feed and carrying six tools, to be applied to the work successively, these tools being mounted in a "turret," so called because it resembles the turret or tower of the "Monitor" pattern of ironclad vessels of war. This lathe will work upon any kind of pieces which can be held in a chuck and which need the successive operation of several different tools. But, while in many features it resembles a lathe, it is unlike the latter in its treatment of small work. A lathe takes a forged shape and trims and alters it; the screw-machine takes the roughened bar and finishes the product, doing the work of blacksmith, helper, fire, boltheader, centring-machine, lathe, lathe-chucks, and even making the hole in which the lathesman tries his work. While it wastes iron, it saves labor, which is of much more value than the iron wasted. In this machine there is a chuck (A) with V-jaws,. which is fast upon the whole arbor of the machine. There is a steadying-chuck (B) on the rear of the arbor, and an ordinary lathe-carriage (C) slides upon the bed and is worked by the usual hand-wheel (D) and rack-pinion. Across this carriage slides a tool-rest (E) worked by a screw and having two tool-posts, one in front and one in rear of the work. This tool-rest works upon an intermediate slide, which fits and slides in the carriage, and is moved in and out a short distance by a cam lever (G), an apron on the front end of the slide carrying the leadscrew nut (H). Resting the cam lever brings the slide outward, and the tool-rest (E) comes with it, and at the same time the nut leaves the leadscrew. The inward movement of the slide is always to the same point, thus engaging the lead-screw, which does not extend to the head of the machine, and resetting the tool. The gear is never changed, different lead-screws being used for different threads. The turret (O) turns on a block (M), which slides on the bed; it has in it six holes, to receive sundry tools, can be turned to bring any of these tools into action, and is secured by the lock-lever (P). The turret slide is quickly moved by hand through the capstan levers (U), which also lock it at any point.{br}
&nbsp &nbsp &nbsp In making a screw the following are the operations of this interesting and valuable machine: The bar is inserted through the open chuck and set against an end-gauge in the turret. The front tool in the carriage cuts the end of the bar; a turning-tool in the turret reduces it at one heavy cut to nearly the right size; a "sizer" brings the body to the exact size, and, an arm with an open die being brought down, the bolt is threaded; a solid die brings it to the exact size and cuts the full thread to the exact point desired; the front tool of the carriage chamfers off the end thread and the back one cuts off the bolt. The bolt being then reversed in the chuck, the top of the head is water-cut finished by a front tool in the carriage, this last operation being deferred until all the bolts of the lot are ready for it. This machine also taps nuts and makes a large variety of lathe-work.{br}

[imageauto|Screw-Cutting Lathe|{UP}/Metal-Working Machines/PL 23 Fig 1.jpg]{br}
The screw-machine exhibited in Figures 1 to 7 is also made for the cheap and rapid manufacture of a very great variety of work of circular cross-section directly from bars of material such as steel, iron, brass, and hard rubber.{br}

[imageauto|Screw Machine Sample Parts|{UP}/Metal-Working Machines/PL 23 Fig 7.jpg]{br}
&nbsp &nbsp &nbsp Some samples of its work, consisting of screws, nuts, and studs, are shown in Figure 7. Bolts and set-screws with hexagonal or square heads are obtained by using stock of that cross-section. Small castings having holes and studs of various shapes and sizes to be finished can sometimes be worked up with great saving of time and labor over the lathe and drill-press. The speed with which these machines will turn out work depends upon the size and shape of the work and upon the material used. Screws such as are shown in Figure 7, if made of iron, can be manufactured at the rate of from fifty to ninety per hour; if of brass, from seventy to one hundred per hour.{br}
&nbsp &nbsp &nbsp The machine (Fig. 1) is operated by working three levers, the workman standing so that one is in front and one at each hand. The lever at the left operates the wire-feed. This mechanism, while the machine is running at full speed, so feeds forward the rod, from which the screw or other piece has been made, as to furnish just enough stock to make another. The handle at the right operates the turret-head, bringing successively six tools to act upon the stock. The centre handle operates the crossfeed and governs the action of two tools, one usually a tool for chamfering, grooving, or knurling, and the other for cutting off the finished piece. In working wrought iron or steel a lubricant such as oil or sodawater is used. To keep the tools sharp longer, so that the work will have a smoother and more accurate finish, a reservoir of oil is provided as shown in the cut. Into the basin-joining part of the frame of the machine is drained the oil, which is strained free from chips and dirt by running through wire gauze into the large tank, from which it can be drawn and used repeatedly, thus reducing the waste to a minimum. The workman starts the machine, adjusts the speed by shifting the belt to the correct step of the cone pulley, opens the valve of the oil-reservoir and adjusts its position until the oil drops at the right place, and gives a double oscillation to the wire-feed lever, by which the stock-rod is loosened, fed forward against a stop in the turret-head, and clamped. Then at each double oscillation of the turret-head lever a new tool designed to do a special part of the work is presented to act upon the stock-rod, and by a double oscillation of the cross-feed lever the piece is chamfered or grooved and cut off, and the machine is ready to recommence the cycle.{br}

[imageauto|Wire Feed for Screw-Cutting Lathe|{UP}/Metal-Working Machines/PL 23 Fig 2 and 3.jpg]{br}
&nbsp &nbsp &nbsp Figures 2 and 3 show the wire-feed in detail. The steel spindle a (Fig. 2) is hollow, to allow the hollow rod b to pass freely through it, the hole through b being a little larger than the largest stock that the machine is designed to work. The conical part of the carefully tempered spring collet (c) fits into a hole ground to a corresponding taper in the hardened steel shell d. Putting (b) in the spindle at (k) so that the surfaces (c') and (b'') coincide, and screwing (d) on the spindle at (k), then, by pressing upon the end of the rod (b'), the conical parts of (c) and(d) will coincide, forcing together the three jaws of the spring collet (c), and clamping the stock-rod passing through it. Collets with different holes are required for different sized rods. The stock-rod has a continual tendency to go forward against (c) (Fig. 3) because of the force transferred from a weight through the bronze chain (a), over a small pulley to the piece (b), which slides freely upon the rod (e). By turning the disc upon b, various sized holes can be brought successively to a common centre, thus forming a very convenient bushing for different sizes of stock. By withdrawing the pressure from the rod (b), the spring collet will retract, allowing the stock-rod to pass through until arrested by the stop in the turret-head, and by renewing the pressure the rod is again clamped, and the turret-head and cross-feed may proceed with their functions. To reciprocate these pressures while the machine is running, the rest of the mechanism shown in Figures 2 and 3 is necessary. In Figure 2, (e) fits loosely upon the spindle (a), as shown in position in Figure 3. The piece (Fig. 2) is virtually a part of the rod (b), the connection being made by screw-pins (f) passing through the slot in the spindle (a), into holes (b') in the rod (b). Hinged to (f) are two tempered steel cam levers, which act against the bevelled surface of the hardened steel nut (g), forcing the rod b forward; the nut(g), after proper adjustment, is held in position by a set-screw pressing a shoe against the threaded spindle; (i) is the fulcrum, which is screwed firmly into the frame of the machine. The steel yoke (h) has one surface of brass, which can be replaced when worn. The cone is fastened to the spindle, so as to allow adjustment with its axis by means of a nut (k), the thrust being taken in both directions by the front bearing intercepted by two hardened steel washers.{br}

[imageauto|Turret Head|{UP}/Metal-Working Machines/PL 23 Fig 4.jpg]{br}
&nbsp &nbsp &nbsp The turret-head can be adjusted in position upon the machine and firmly clamped by the bolt a (Fig. 4). As the turret slide (b) moves to the left, the turret (c) remains firmly locked in position, the forward motion of the turret slide being arrested by an adjustable stop-screw (d). By moving the slide to the right a locking-pin is withdrawn from a hole in the bottom of the turret by a lever upon which a heavy spring presses and holds the pin in the hole. As the slide moves to the right, the end of the lever rides under a steel piece, which is free to swing in the opposite direction and withdraws the pin from the turret. As the movement of the slide continues, a ratchet-pawl engages with a ratchet-wheel, and turns the turret, the pawl being brought to its neutral position by a coil-spring. Meanwhile, a projection upon the lever has passed from under the steel piece, and the spring is acting, so that as soon as the hole in the turret comes under the pin, the pin is forced in. At this instant the relative motion of the slide and slide-rest is arrested by the contact of two lugs, so that in rapid working there is no danger that the locking-pin will miss the hole.{br}

[imageauto|Tool Holders|{UP}/Metal-Working Machines/PL 23 Fig 5.jpg]{br}
&nbsp &nbsp &nbsp The principal tool-holders used in the turret-head are shown in Figure 5. (A) is the "box-tool," which, containing two cutters—one for roughing and one for finishing—can easily be taken out and ground. The shape of the box-tool allows easy access for measuring the work. (B) is a die-holder, the die being held by three screws, which allow the die to be so adjusted as to swing concentrically with the spindle. The part (b') fits freely upon (B) and is clamped in the turret. (C) is a tap-holder and works the same as the die-holder; (e) is for holding hollow mills and other tools,and d is the stock, with which the rapidity of the wire-feed is gauged.{br}

[imageauto|Cross Feed|{UP}/Metal-Working Machines/PL 23 Fig 6.jpg]{br}
 Figure 6 shows the cross-feed.{br}

<h1>Drills and Drilling-machines</h1>{br}
&nbsp &nbsp &nbsp To bore a cylindrical hole in wood or metal it suffices to place upon the material a pointed steel tool provided with scraping- or cutting-edges and to rotate it with a constant pressure in the direction of its axis. A tool of this kind is called a "drill". The forms of the cutting-edges vary greatly, according to the different materials to be drilled.{br}

<h4>Metal Drills</h4>[imageauto|Metal Drills|{UP}/Metal-Working Machines/PL 24 Fig 1-10.jpg]{br}
&nbsp &nbsp &nbsp Of the drills for metals illustrated, Figures 1 and 2 represent straightway drills; Figure 3 a drill for boring brass and soft metals; Figure 4 a countersink; and Figure 5 a countersink and drill combined. Figure 6 shows the ordinary single-cutting drill, in which the point is nearly a rectangle formed by only two facets symmetrical to the axis. Drills of this kind, being liable to run out of centre, have been improved by increasing the length of the parallel portion next to the edges and by maintaining it at a width equal to the diameter of the bore (Fig. 7). In the drill shown in Figure 8, which is intended for lathe use, there is a single edge on the end of a semi-cylinder, the central point, as in Figure 9, being wanting. The twist-drill (Fig. 10) may be considered the most complete form for metals, continuous removal of shavings being effected through two helical channels.{br}

<h4>Metal-drill Braces</h4>[imageauto|Metal Drill Braces|{UP}/Metal-Working Machines/PL 24 Fig 11 and 12.jpg]{br}
&nbsp &nbsp &nbsp For manipulating drills the crank-brace (Fig. 12) is mostly used. The "feed" of the drill is effected by a powerful screw, with a box in a horizontal arm of a frame connected to the material to be drilled. While the right hand moves the handle of the brace in a circle, the left effects gradual advance of the drill by a bar pushed through the head of the feed-screw. A suitable combination of crank-brace and ratchetbrace is shown in Figure 11. The brace does not receive a continuous rotation, but a pendulum-like oscillation, through which the advance of the drill by means of pawl, ratchet-wheel, and screw is automatically effected.{br}

[imageauto|Rachet Drills|{UP}/Metal-Working Machines/PL 24 Fig 14 and 15.jpg]{br}
 Figures 14 and 15 represent ratchet-drills employed by engineers, machinists, bridge-builders, ship-builders, boiler-makers, etc.{br}

[imageauto|Hand Drills Clamped to Bench|{UP}/Metal-Working Machines/PL 26 Fig 3.jpg]{br}
&nbsp &nbsp &nbsp Figure 3 exhibits a hand-drill which can be fastened to a work-bench or to the flange of a casting by means of a clamp and a stud, or can be permanently bolted to a bench or any flat surface. The post and arm are both round, and are held in split bearings, which allow the drills to be placed in any position and at any angle. The crank-handle, to suit the size of the hole being drilled, is adjustable, and it can be used either at the end of the arm (B) or at the end of the spindle (A).{br}
 
<h4>Vertical Drilling-machines</h4>
[imageauto|Vertical Drilling Machine|{UP}/Metal-Working Machines/PL 24 Fig 13.jpg]{br}
&nbsp &nbsp &nbsp Drilling-machines are so arranged that of the two motions (rotation and rectilinear translation) to be imparted to the tool the first is derived from a transmitting shaft driven by power, while the other is effected either automatically or by the hand or the foot of a workman. Figure 13 shows a vertical drilling-machine for metals, in which the material to be drilled is secured to a table which can be adjusted at any height desired. The drill, fixed in a vertical spindle, receives its rectilinear motion by pressing down a treadle and its rotation by bevel-gear, from a revolving belt-driven shaft. The speed for every material has to be determined by experience, but to give different rates for drills of different diameters "stepped" or cone pulleys are provided. The drill-spindle, in order to acquire the motions to be imparted to it, passes through the hub of one of the bevel-gears, the latter being so connected to the frame that it can be turned, but not shifted vertically.{br}

<h4>Vertical Automatic Drilling Machine</h4>{br}
[imageauto|Vertical Automatic Drilling Machine|{UP}/Metal-Working Machines/PL 24 Fig 17.jpg]{br}
&nbsp &nbsp &nbsp A vertical automatic drilling-machine is shown in Figure 17. The drill-spindle is turned by a horizontal driving-shaft with cone pulleys, and a counter-shaft placed near the ceiling. By special gearing, consisting of two pairs of spur-wheels, the number of velocities can be increased to double the number of belts. Automatic advance of the drill is derived from the same driving-shaft by a belt-gearing (which can be run on three different pairs of pulleys, as seen on the right of the Figure), a horizontal counter-shaft, a worm-wheel gear, a vertical auxiliary shaft, a pair of spur-wheels, and a nut and spindle. The latter being connected with the frame for sliding and with the drill-spindle for rotating, the rotation communicated to the nut is changed into vertical sliding of the drill spindle.{br}
&nbsp &nbsp &nbsp Some machines for drilling and boring give good examples of aggregate motions, the spindle carrying the cutting-tool turning rapidly and at the same time advancing slowly lengthwise. Suppose a screwed spindle to have upon it a spur-wheel and to bear a nut upon which there is a smaller spur-wheel; then, if these two spurs have different speeds, the spindle will not only turn, but will also advance lengthwise, and the rates of turning and advancing (or feeding) may be varied at will independently of each other. A self-acting drilling-machine which is not automatic turns the wheel attached to the nut by a power-driven bevel-wheel, while the wheel upon the spindle is worked through another one, upon a shaft having a wheel turned by hand at will. The drill-spindle has in its lower part a groove, and the inside of the tube, which bears the wheel giving the rotation, has in this groove a projection or feather, so that the spindle can move lengthwise, as though it were a part of the tube. In some machines a rack and a pinion take the place of the screwed spindle. The self-acting part consists of a small cone pulley, whose axis has a second endless screw and just over the end wheel a worm-wheel, which may be slid into gear, so that it can be turned by the driving-shaft. Bodmer's self-acting drilling-machine has a screw-thread upon the drill-spindle, while a projection upon the inside of the boss of the lower wheel fits into a groove, so that the spindle can pass through the wheel, although they must turn together. A pipe-like nut having a wheel at the bottom receives the spindle. One pinion brings the drill down to the work, the other raises it, and the fine feed is the result of the combination of these two rates. In Whitworth's friction-drill the spindle has two worm-wheels, embracing its screwed portion upon opposite sides. If not permitted to turn, they form a nut which causes the spindle to move lengthwise; if free to move, the spindle will neither advance nor recede. The application of friction to retard them more or less makes the feed coarse or fine.{br}

[imageauto|Elliott Drill Press|{UP}/Metal-Working Machines/PL 25 Fig 12.jpg]{br}
&nbsp &nbsp &nbsp In the Elliott drill-press, shown in Figure 12, the cone is hollow throughout and terminates in two sleeves, which constitute the journals upon which the cone revolves. Their bearings are of brass, made in two parts, and held in place after the manner of engine-lathes: the weight of the cone is taken upon a rawhide washer that rests upon the top of the lower brass bearing, which latter has a flange projecting upward around the washer, for the purpose of retaining the oil. The steel spindle, which carries the drill-chuck, passes through the sleeves, each of which forms for it a long bearing; the spindle is made to revolve with the cone by the driver, which is pinned to the spindle and whose ends embrace two rods, which form a part of the cone. Around the spindle and extending from the driver to the bottom of the cone is a steel spiral spring, which serves as a counterbalance to the spindle and chuck. Power to feed the drill is applied to a collar having a bearing directly over the chuck. The wear incidental to the thrust of feed-lever is taken by a rawhide washer. The lever, which is attached to the collar, is actuated by hand- or foot-levers through the medium of a rod inside the column; and when desired, the descent of the spindle may be accurately stopped at any given point by means of a clamp collar. The lower end of the hand-rod is connected with the inner arm of a segment, which is free between the forked ends of the hand-lever and foot-lever, either or both of which levers may be connected with the segment at any point by the insertion of pins. By loosening a set-screw the length of hand-lever may be changed to suit different workmen.{br}

<h4> The Sensitive Drilling-machine</h4>[imageauto|Sensitive Drilling Machine|{UP}/Metal-Working Machines/PL 26 Fig 5.jpg]{br}
&nbsp &nbsp &nbsp This machine (Fig. 5) was designed with particular reference to the accomplishment of rapid and accurate work with small drills, and at the same time to obviate as far as possible all danger of their breakage. By small drills are meant drills from of an inch in diameter, the size of an ordinary lead-pencil, down to .015 of an inch in diameter, the size of a cambric sewing-needle. One of the chief requisites of a drilling-machine for this purpose is a true- and light-running spindle. The usual mode of running a spindle is to attach a pulley to it direct and give it motion by a belting from another driven pulley. The objections to the old style were, first, the strain on the spindle by the belt tension, rendering it liable to spring; and secondly, the wear on the boxes or journals in which the spindle ran, occasioned by the strain and pull of the belt being always from one direction, with the consequent certainty of wearing the boxes out of round.{br}

[imageauto|Sensitive Drilling Machine Top Arm|{UP}/Metal-Working Machines/PL 26 Fig 4.jpg]{br}
&nbsp &nbsp &nbsp Through the top arm of the drill-frame (Fig. 4) is inserted a hollow sleeve, whose lower end comes nearly flush with the frame—that is, it only extends through a sufficient length to provide a good bearing for the pulley to run on. The drill-spindle runs on the inside of this sleeve, and the pulley, with a hub somewhat longer than the upper end of the sleeve, on the outside. The spindle has a small groove or key-way cut lengthwise. In the upper end of the pulley-hub a bushing is made fast, and in this bushing is the key fitting the spline in the spindle, which drives it when the pulley is revolved and at the same time provides for vertical spindle motion. Hence there is no belt tension on the spindle.{br}
&nbsp &nbsp &nbsp The next important point is in securing a feed of so sensitive a nature that the operator can at all times judge of the exact power applied and the resistance of the work to the drill-point. This feature is covered by balancing the weight of the spindle-chuck, etc., by a flat coiled spring. Through the lower or adjustable arm is run a pinion-shaft, whose pinion drives into a rack, which is in the form of a sleeve, in which the spindle runs, and is held in place vertically in the spindle by the nut and collars shown. On the outer end of the pinion-shaft is keyed a disc, into which the lever is set, while on the inside thereof is a projecting pin, over which is placed the end of a flat coiled spring. The spring is coiled in a spring box of the same diameter as the disc referred to, and to adjust the spring tension is arranged to revolve on a boss or projection on the frame. When the spring is so set that the tension thereon just balances the weight of the spindle, its attachment, lever, etc., the spring box is made fast by a set-screw to the frame, and the lightest touch on the lever will raise or lower the spindle. When in operation, the only resistance to the hand is that of the material being drilled, and the expert operator can force his drill up to its safety limit . By loosening a hand-nut on the back of the post the lower head can be set at any height, allowing for quick adjustment for varying thicknesses of work.{br}
&nbsp &nbsp &nbsp One more very essential feature in light drilling is that the tool shall run steady without vibration, especially about the spindle. A recent improvement makes the top arm in two pieces planed together, to slide on a tongue and groove, and provided with an adjusting screw and locknut . With this arrangement an endless leather belt can be used to drive from the spindle-driving pulley on the back cone to the spindle pulley, and thus do away not only with the vibration caused by the lacing running over the pulley at high speed, but also with the trouble and expense of lacings and the necessity of providing means for keeping the belt at the proper tension at all times. The drill-table swings around on the head of the column, so that the supplementary table underneath can be used, or by removing the latter stand a bell-shaped stand can be used in its place. The support for this lower table- and cup-stand is adjustable on a slide to any height. Drills having the essential good points of this one are made having two, three, four, and even more, spindles.{br}

[imageauto|4 Spindle Drilling Machine|{UP}/Metal-Working Machines/PL 24 Fig 18.jpg]{br}
&nbsp &nbsp &nbsp The arrangement made for driving the two-, three-, and four-spindle drills with a single endless belt is a great convenience, doing away with the care required to keep up a short belt for each spindle.{br}

<h4>Radial Drilling-machine</h4>
[imageauto|Radial Drilling Machine|{UP}/Metal-Working Machines/PL 24 Fig 16.jpg]{br}
&nbsp &nbsp &nbsp As it frequently happens that several holes are to be drilled in the same direction in masses of metal which are heavy and difficult to move, the vertical drilling-machine is sometimes so arranged that within a certain range the drill-spindle can be shifted to every desired place without detriment to the motion to be imparted to it from the driving-shaft. If this is attained by radially pushing the head containing the drill-spindle upon a horizontal arm and by rotating this arm, this kind of machine is called a "radial" drill (Fig. 16). The arm rotates around a cast-iron column, having in its axis a vertical shaft, which receives at its lower end a rotation from the horizontal driving-shaft by a bevel-gear and transmits it on the upper end, by another bevel-gear, to a horizontal shaft (not plainly shown in the Figure), which participates in the motion of the arm as well as in the rectilinear displacement of the drill-spindle carriage. This shaft being connected (by spline and groove) with the bevel-gear driving the drill-spindle, the connection of movement between the drivingshaft and drill-spindle remains the same for all possible positions of the drill. The drill-feed motion is derived from its rotation in the same manner as in the machine represented by Figure 17, except that here the feed can also be executed by hand by turning the hand-wheel, at the right of the drill-spindle. The material to be drilled is secured to the horizontal or vertical surface of the frame, which is provided with T-grooves, or, if very large and heavy, is placed directly upon the floor.{br}

<h4>Single Vertical Drilling-machine with Combined Motor</h4>
[imageauto|Single Vertical Drilling Machine|{UP}/Metal-Working Machines/PL 26 Fig 1.jpg]{br}
&nbsp &nbsp &nbsp In the single-spindle drilling-machine, represented in Figure 1, the working machine is combined with a motor, forming in this case a vertical drillingmachine with an oscillating steam-engine. Such a combination offers many advantages. The working machine being entirely independent of other machines, the uniformity of its running is not affected by nor does it disturb the others; power is used only while the machine is running, and portability, applicable in the construction of large materials—bridges, shiphulls, etc.—is obtained by conducting the power (steam, water, or compressed air) from its source to the machine. A bevel-pinion upon the engine crank-shaft drives a large bevel-wheel, whose shaft carries the drill-bit. The feed is by hand, the vertical shaft upon the large bevelwheel being hollow and internally threaded. This machine has its analogy in those mortising-machines for wood in which the mortise is made with straight sides, flat bottom, and semicircular ends by a rotating auger having a traverse at right angles to its axis, the ends being squared by a mortising-chisel after the auger-bit has done its work. With the metalworking cotter-drill, if it be desired to have square ends to the groove, they may be either chipped out with a hand-tool or squared by a slottingtool. In the ordinary drill the work is held stationary, and the tool, whose axis is vertical, is given rotation, while its feed is only in the direction of its axis. In the cotter-drill the tool is given feed in the direction of its axis, and the work is also fed at right angles thereto.{br}

<h4>Cotter Drilling-machines</h4>[imageauto|Mortising Machine|{UP}/Metal-Working Machines/PL 25 Fig 9.jpg]{br}
[imageauto|Cotter Drill Machine|{UP}/Metal-Working Machines/PL 25 Fig 10.jpg]{br}
[imageauto|Cotter Drill Machine|{UP}/Metal-Working Machines/PL 25 Fig 11.jpg]{br}
&nbsp &nbsp &nbsp Figures 9, 10, and 11 show an admirable general application of drilling-machines, in which, besides the two motions previously referred to, there is added a third—namely, a rectilinear translation of the material at right angles to the drill axis (Fig. 9), or, with the material remaining stationary, the same motion is imparted to the drill, drill-spindle, and appurtenances. Suppose the drill has penetrated the material to a certain depth and this forward-and-backward motion there takes place within certain limits, the drill being fed sidewise every time it is reversed; then, instead of a circular hole, the result will be a groove with semi-cyliudrical ends. The ends of these drill-cut grooves can subsequently be readily made rectangular by means of a chisel. These machines form a transition from drilling- to milling-machines.{br}

[imageauto|Cotter Drill Bits|{UP}/Metal-Working Machines/PL 25 Fig 1-5.jpg]{br}
&nbsp &nbsp &nbsp The bits used for them are shown in Figures 1 to 5. Figure 1 represents a double-pointed drill and Figure 2, a rose-bit. Figures 3 to 5 are reamers.{br}

<h4>Boring and Turning-mill</h4>
[imageauto|Boring & Turning Mill|{UP}/Metal-Working Machines/PL 26 Fig 2.jpg]{br}
&nbsp &nbsp &nbsp In the boring-machine proper the work is stationary and the tool rotates about an axis coincident with that of the piece to be bored. The tool has at the same time a lengthwise motion parallel with that of the work being bored; and if taper or other noncylindrical boring is done, the tool has also an in-and-out motion at right angles to the axis of rotation. In boring- and turning-mills the work rotates, the tools having practically the same motions as upon an ordinary lathe, except that in the lathe the axis of rotation is always horizontal and in the boring- and turning-mill it is generally vertical.{br}
The boring- and turning-mill is now a necessary part of the outfit of any large machine-shop. The Niles type, shown in Figure 2, is a leading example. There is a very heavy table, driven by spur-gearing and having a long massive spindle running in bearings adjustable for wear. For light work the table is carried only upon a steel step, but for heavy work the step is relieved and the table lowered upon an annular bearing under its outer edge. The driving-belt is at the side. The crossrail, which carries the tool-heads, is raised and lowered by power. The tool-bars, which are counterbalanced by weights, can work at any angle, can be operated from the end of the rail by hand, together or independently, and can also be worked at the saddles by a quick hand movement, while the feeds are automatic in every direction, and also variable in very great degree. The right-hand saddle has quick traversing movement by hand in addition to a slow hand movement and the feed. Besides boring and turning, this mill, by an attachment, can without clamping do pulleyturning on a mandrel, slotting and key-seating, cylinder-boring, threadcutting in large valves, grooving in hoisting-apparatus, drums, etc.{br}

<h1>Metal Planers</h1>{br}

 <h4>Planer Tools</h4>
[imageauto|Planer Tools|{UP}/Metal-Working Machines/PL 25 Fig 6-8.jpg]{br}
&nbsp &nbsp &nbsp The tools for planing metals (Figs. 6-8) are of larger dimensions than those for wood and have a greater cutting-angle, corresponding to the greater resistance of the material. They usually have a convex edge or an angular cutting-point, and consist either of a single piece of steel (Fig. 8) or of a short piece set in an iron holder (Figs. 6, 7). These tools are used only in machines applied to metal-planing.{br}
&nbsp &nbsp &nbsp Though nearly all the machines for working wood, and commonly called "planing" machines, are substitutes for the hand-plane, they are actually cutting-machines, since they work with revolving tools. Metal-planing machines may be divided, according to the direction in which the separate cuts are executed, into vertical and horizontal, and the latter may be divided into planing-machines with movable irons and those with stationary' irons.{br}

<h4>Horizontal Planing-machines</h4>
&nbsp &nbsp &nbsp Most of the planing work upon metal, as upon wood, is done in a horizontal direction. In small work the material is held still and the tool is given a comparatively slow working-stroke and quick return, the feed being effected after the working-stroke is completed. Such machines are termed "shapers".{br}
&nbsp &nbsp &nbsp For large work, by some strange inconsistency, the piece to be operated upon is given horizontal movement for the working-stroke while the tool is held still, the feed for the new cut being effected after the workingstroke is made, and the return or idle stroke being comparatively rapid.{br}

[imageauto|Horizontal Planing Machine|{UP}/Metal-Working Machines/PL 27 Fig 5.jpg]{br}
&nbsp &nbsp &nbsp The Horizontal Planing-machine with stationary tools  represented in Figure 5, holds the tool in a support, which allows it to be placed obliquely and to be shifted vertically. The support itself can be shifted upon a horizontal prism extending the whole width of the machine. A slight lateral feed (generally also a shifting in the vertical sense) can thus be imparted to the tool by a special mechanism after each cut. The piece of metal is secured by suitable screws, stays, etc., to a cast-iron table, which can be horizontally shifted upon a long and strong cast-iron bed by a partially-executed prismatic guide. Upon the under side of the table is a rack, which meshes with a gear upon a horizontal shaft and receives a back-and-forward motion from the driving-shaft. Thus it will be seen how after suitably setting the tool the surface of the piece of metal can be smoothly planed. To get sufficient space for working articles of some height the horizontal prism carrying the support is so arranged that it can be vertically shifted on the front side of two cast-iron uprights screwed or cast to the above-mentioned cast-iron bed and connected at the top by a cross-piece. The support is raised or lowered by two vertical screws of equal pitch, which can be turned simultaneously and at the same speed by a horizontal shaft above the uprights. Fastened on the side of the table, at a distance from each other corresponding to the length of the piece of metal, are two tappets, which by striking against a short lever reverse the table motion at the proper time and simultaneously effect the lateral shifting of the tool-bit.{br}

<h4>Whitworth Planer</h4>
&nbsp &nbsp &nbsp To effect its reverse motion the Whitworth planer has a combination of three pulleys with three bevel-wheels. There are upon one shaft three pulleys, the central one of which is idle and rides loose; the outer pulley is keyed to a shaft ending in a bevel-wheel, and the pulley at the inner end of the set fits upon a pipe, through which the shaft passes, and upon which is a bevel-wheel with its teeth pointing toward the first bevel-wheel. At the end of the shaft, which is to be reversed, is a bevel-wheel, which engages with both the other bevel-wheels. When the belt is shifted from the inner to the outer one of the three pulleys, the shaft is reversed; if kept upon the middle pulley, there is no motion. The objection to this arrangement is that the motion is at the same speed in each direction, necessitating a reversing-tool or "jack in the box." This is worked upon the same principle as the hand-drills, in which the rotation is effected by pushing a nut up and down a rod, upon which there is formed a screw of rapid pitch, so as to cause the spindle to rotate first in one and then in the other direction as the nut rises and falls.{br}

<h4>The Sellers Planing-machine</h4>
[imageauto|Seller's Planing Machine|{UP}/Metal-Working Machines/PL 28 Fig 1.jpg]{br} &nbsp &nbsp &nbsp (Fig. 1), has its reciprocating motion given by spiral gearing without the intervention of bevelwheels, the intention being to obviate the chatter-marks caused by other kinds of gearing. The reciprocating motion is not produced by shifting belts, but by friction clutches, and the driving and shifting are so positive that the machine will plane to a shoulder. The table has one plane and one flat angular way, the latter having four bearing-surfaces, two to carry the weight and two to take the side-thrust. The table is guided laterally by two surfaces, both nearly vertical. The feed is distinct from the motion of the table and is driven positively from a slow-running pulley by an ingenious appliance for transmitting and arresting motion. It is caused by adjustable stops on the table, and takes place while the machine is reversing, and at the end of the back stroke if desired, no matter in which direction the feed is working. The machine is operated from either side by levers that control the table motion and can at will at the same time cut loose and arrest the feed, so that the table can be run past the stops as often as required for examination or adjustment of the work. The cross-head, which incloses the saddles, takes up the wear. On planers of 36 by 36 inches, and larger, when fitted with two saddles on one cross-head, the feed-screws and rods to each are separate, so that each can be operated in all respects independently except in the amount of feed, which will be the same for both saddles; the amount of feed to each saddle can also be made independent. The feed is adjustable, from one whole revolution of the feed-screws down to nothing, by an infinite gradation, there being no teeth in the feed-ratchet to limit the changes. Planers 25 by 25 inches, and larger, are fitted with a tool-lifter, raising both tools on the back stroke, no matter in which angle the planing-tool may be advancing. The tools of both vertical slides stand in line with the main tools, are operated by separate feed, and can be lowered below the top of the table when not in use. For the cross-head large planers have lifting machinery operated by friction-wheels, which can be held to their work without much effort, but which, to avoid accidents, stop as soon as the workman releases his hold on the lever. Machines up to 54 by 54 inches, inclusive, have a return speed eight times greater than the speed of cut, or about 150 feet per minute. Machines of 60 inches, and larger, have a return speed six times greater than the speed of cut, or about 110 feet per minute. Machines of the latter class stand parallel with the lineshaft, economizing room in the shop, and, having no shifting-belts from the counter-shaft, the position of the latter is not so limited as on old styles.{br}
&nbsp &nbsp &nbsp The Open-side Planer differs from the ordinary type in having one side entirely open, so that very wide work may be taken in. The plate-planer is for planing straight and smooth and bevelling the edges of boiler and bridge-plates of wrought iron. The rotary planer is practically not a "planer," but a gigantic milling-machine with cutters having adjustable teeth. In the pit-planer, which was once used for very heavy work, the material is held stationary and the tool is given traverse, as in a shaper, so that we find the motion given to the tool for both the lightest and the heaviest work—an apparent inconsistency.{br}

<h4>Shapers</h4>
[imageauto|Shaper|{UP}/Metal-Working Machines/PL 27 Fig 3.jpg]{br}
[imageauto|Shaper|{UP}/Metal-Working Machines/PL 27 Fig 4.jpg]{br}
&nbsp &nbsp &nbsp Horizontal metal-planing machines with moving tools and stationary work, also called "shaping-machines" or "shapers," are represented by Figures 3 and 4. The head, carrying on the front end a special tool, receives alternating motion in a horizontal guide by a mechanism similar to that for vertical machines. The piece is secured to a bracketlike table, which is step by step pushed forward horizontally by a rack and pinion (Fig. 4). Sometimes the table is stationary and the lateral position of the portion containing the guide is attained by a rack and pinion and a screw (Fig. 3), the result in both cases being the execution of a level plane on the piece of metal. By securing the latter to a horizontal spindle (between two cones) and imparting a step-by-step rotation, a cylindrical surface will result. This manner of shaping cylindrical surfaces is suitable where they are not to be made over the entire circumference of the piece, and hence cannot be made in a lathe.{br}

<h4>Vertical Metal-planing Machines </h4>
[imageauto|Slotter|{UP}/Metal-Working Machines/PL 27 Fig 1.jpg]{br}
[imageauto|Slotter|{UP}/Metal-Working Machines/PL 27 Fig 2.jpg]{br}
&nbsp &nbsp &nbsp The arrangement of vertical metal-planing machines (generally called "slotters," or "slotting-machines") is illustrated in Figures 1 and 2. The tool is on the lower end of a vertically guided carriage, which receives an up-and-down motion by a crank and pitman from a driving-shaft provided with a cone pulley or by intermediate wheels and crank-gearing. The piece to be worked (in Figure 1 a spur-wheel, whose hub is to be provided with a keygroove) is secured to a horizontal table provided with planed grooves. This table can be revolved around a vertical axis as well as pushed in two horizontal directions crossing each other at a right angle. These three motions can be executed either by hand (by turning three cranks) or by suitable mechanism from the driving-shaft. Hence, after each cut the piece can be so placed that the resulting surfaces make up a level or a surface belonging to the ordinary surfaces of a cylinder. With such a machine it is, for instance, possible completely to finish to a scribed line the clearance spaces between the teeth of a spur-wheel.{br}

[imageauto|Auxilary Planer Table|{UP}/Metal-Working Machines/PL 27 Fig 6.jpg]{br}
&nbsp &nbsp &nbsp By arranging the table (fig. 6) so that its upper portion can be placed obliquely, conical shapes can be completely finished.{br}

<h1>Milling-machines</h1>{br}

&nbsp &nbsp &nbsp These machines are constructed so that while the tool rotates, the work has a traversing motion, and often, in addition, an intermittent partial rotation about its own axis, or a cross-feed, so as to bring new portions under the action of the rotating cutters.{br}

<h4>Universal Milling-machines </h4>
[imageauto|Universal Milling Machine|{UP}/Metal-Working Machines/PL 28 Fig 2.jpg]{br}
[imageauto|Universal Milling Machine Work|{UP}/Metal-Working Machines/PL 28 Fig 3-5.jpg]{br}
&nbsp &nbsp &nbsp Universal Milling-machines (Fig. 2) are termed "universal" from their almost unlimited variety of operations. With rotary cutters they in many instances do more accurate and expeditious work than the planer or shaper, and they also turn, bore, drill, and flute taps and reamers, and cut gears and spirals. They have all the movements of the plain milling-machines, and, in addition, the table is fed automatically at any angle to the axis of the spindle. The spiral head is so made and connected with the feed-screw that a positive rotary movement may be given to the work, and by index mechanism the periphery of the work may be divided into an equal number of parts. The knee can be moved vertically and the saddle holding the spiral bed can be moved parallel with the axis of the main spindle. Motion is transmitted from the feed-cone through a feedshaft to a bevel-gear and clutch at the end of the bed. If it is desirable to employ this feed when cutting a left-hand spiral or at any time when there is considerable distance between the end of the bed and the feedcone, the shaft is lengthened with an extension-rod. A series of graduations shows the angle to the axis of the spindle at which the table is fed, and index-dials record the vertical and horizontal knee movements in thousandths of an inch. Motion is communicated from the feed-screw to the spindle of the spiral head through change-gears, bevel-gears, and a worm and worm-wheel. The change-gears regulate the rotary movement of the spindle, or of the work, relative to the speed of the feed-screw, and any spiral of the sixty-eight provided for may be cut without interfering with the divisions obtainable from the index-plate on the spiral head. The spindle may be given any portion of a revolution or may be rotated continuously. There runs through it a taper hole, which receives the collets and arbors used in the main spindle. The front end of the spindle is fitted to receive a chuck. The worm-wheel is so made that it may be adjusted to compensate for wear. The worm-shaft runs in steel bushings, which also serve as a spindle-box pivot. The front end of this box may be elevated or depressed, so that the spindle can be set at any angle from vertical to 5° below horizontal. Every intervening point is indicated by graduations on one of the upright sides of the spiral head, and the head may be held by a clamp-bolt and the spindle left to revolve. A turn of the worm-shaft moves the work or spindle 1/40 of a revolution; hence, by use of the index-plate, a turn of the worm-shaft may be subdivided into various parts. The necessity of counting the holes when dividing the work is obviated by using a sector in connection with the index-plate. By the raising-block the spiral head may be set at any angle on the bed. The vise-base is round and can be clamped upon the bed at any angle. This machine is also constructed with an overhanging arm, to support the outer end of the arbor carrying the cutter.{br}

<h4>The Milling-tool</h4>
&nbsp &nbsp &nbsp may be regarded as a great advance upon the grindstone, and, for certain purposes, as greatly superior to the emery- and corundum-wheels, particularly for removing unnecessary masses of metal and for bringing pieces down to a desired profile. It may be considered as a rotating planer or shaper-tool. By its use the cheap and rapid production of desired profiles may be effected by power with great uniformity and perfection of result. Its cut is usually in straight lines; as a general rule, the object to be milled is not rotated. In some machines the cutters have only a rotating movement and the work is fed to them in straight lines; in others the cutter has a traverse and the work remains fixed; while in some machines both the cutter and the work are fed. The metal-milling machine finds its high-speed counterpart in the planing, matching, moulding, and tenoning wood-working machines employing cutters upon a rapidly rotating shaft, the blades having a working length equal to, or greater than, the width of the surface to be removed, and their profiles effectively corresponding to the outline of surface to be produced. The milling-cutter as sometimes used is akin to the rotating drill; again it resembles in its operation and product the routing-machine. Countersinking-machines show good examples of both such resemblances, some of them working both with the cylindrical periphery and with the end of the rotating cutter-bit. Milling-cutters are either solid—in which case they always lose their size as they are worn by work and sharpening (sometimes losing in effectiveness or working diameter and thickness for the same reason)—or have their cutting-edges so disposed with regard to the mass and the cutter, and with reference to the body to be worked, that even as they are ground down they make the same size and profile of cut. The latter is a most desirable feature, and exists nowhere in greater perfection and to greater advantage than in cutters for working out the spaces between the teeth of gearwheels.{br}

<h4>Milling Operations</h4>
[imageauto|Milling Operations|{UP}/Metal-Working Machines/PL 29 Fig 1-24.jpg]{br}
&nbsp &nbsp &nbsp Figures 1 to 24, which the following explanation will enable the reader to understand fully, are exceedingly interesting. Figure 1 shows how hexagon nuts or heads of bolts are milled with a single cutter; Figure 2, how a number of nuts while strung on a mandrel are milled at one time with two cutters; Figure 3, how a number of caps are milled, and how at the same time their sides and bottoms are accurately finished; Figure 4, how a T-slot is milled having a groove milled or planed to the proper depth; Figure 5, how a V-slot is milled; and Figure 6, how the guides of a housing are milled. This can be done with a cutter the width of the guide or with a saw about ¼ inch thick, finishing one side and then the other. A small cutter should then be applied to finish the inside bearings. The housing requires but one chucking. Figure 7 shows how to turn out a hole with a boring-bar arbor. Various work can be drilled and bored out to advantage in this way, either by bolting the work on the table, by gripping it in a vise, or by holding it between centres. Figure 8 shows how to mill a key-seat in a vise or between centres; Figure 9, how to mill a taper-reamer; Figure 10, how to cut a number of gearwheels when strung on a mandrel; Figure 11, how to mill a tap; and Figure 12, how to hob a worm-wheel after the teeth are cut. The latter operation gives the teeth the proper shape, so that the shafts will stand at right angles to each other. Figure 13 shows how to cut off pieces of metal, and Figure 14 how to mill a thread-chasing tool, the milling-cutter to be V-shaped and at an angle of 60°. First one side and then the other can be milled without re-chucking. Figure 15 shows how to mill an angle, finishing, at the same time, the sides and bottoms; Figure 16, how to mill a slot with a small cutter; Figure 17, how to mill a fork true with its round shank, one end being held in a universal chuck, which is screwed on the spindle of the indexing centre, and the other in a steady-rest; Figure 18, how to cut a rack; Figure 19, how to mill boxes perfectly true with the hole; Figure 20, how to mill an angular cutter; Figure 21, how to index dial-plates, the tool not revolving; Figure 22, how to mill a cam; and Figure 23, how to mill a friezing-bit for wood-work. First the sections are milled out with a square-faced cutter, and then the cuttingedges are milled by placing a right-and-left angular cutter on the millingarbor. These bits can be milled complete before removing them from the mandrel. Figure 24 shows how to cut off round or square stock by placing the universal chuck on the main spindle and using the overhanging arm for a length-gauge.{br}

<h1>The Automatic Gear-cutter</h1>

[imageauto|Automatic Gear Cutter|{UP}/Metal-Working Machines/PL 23 Fig 8.jpg]{br}
&nbsp &nbsp &nbsp  This machine (Fig. 8) is used for automatically cutting or milling teeth upon the periphery of blank wheels for cog-wheels, or, as they are more properly termed, gear-wheels. To cut gears it was formerly necessary, when the means of the manufacturer were limited, for the operator to put in his entire time at the machine, since, after having the blank wheel and cutter in position, he had to feed the cutter through by hand, withdraw it, and then give the divisions on worm-gear or dial, repeating this operation as each tooth was cut on the wheel. With the gear-cutters known as "half-automatic" the operator goes through the same work, with the exception that the cutter feeds itself through the wheel and then stops. The workman then withdraws the cutter, gives the required divisions by hand, sets the self-feed, and then proceeds, repeating the operation for each tooth on the wheel. Nearly his whole time and attention must be given to this machine when in operation, because it feeds the cutter only through the teeth.{br}
&nbsp &nbsp &nbsp  With the automatic gear-cutter the workman can without attention cut either bevel-, spur-, worm-, or face-gears, and after the machine has been set and started it can be run at a slight expense. He sets the blank to be cut, adjusts the machine and starts it running, and then can go about other work and let the machine take care of itself. The machine feeds the cutter through the wheel, draws out the cutter, and makes every change or division of the worm-wheel itself. It makes the divisions with perfect accuracy, the dividing-disc making only one revolution for any number of teeth; and when properly set, mistakes are impossible. In a handmachine mistakes are liable to, and often do, occur. When done cutting a wheel, the machine strikes a gong, thus notifying the workman to come and put in another blank. It is constructed of the following principal parts. The main frame is in the shape of the letter L, upon the front face of the vertical portion of which are two V-tracks, placed for the alignment of a vertically movable head, which contains the barrel and spindle for holding the work, this spindle or work-mandrel being inside the barrel. To the outer or rear end of this barrel is fastened a worm dividing- or master-wheel. Alongside this master-wheel, but fastened to the movable head, is suspended a back or frame. The worm-shaft, engaging with the master-wheel, is supported from this back, as are also the bracket for placing the various combinations of change-wheels for dividing purposes and a one-revolution stop-shaft cam and trip. To the end of the wormshaft, opposite to the end on which the change-wheels are placed, is a slipping friction-wheel, which is driven from the counter-shaft, and which has a tendency to cause the shaft to revolve; but it is kept from doing so by the stop-shaft cam. This worm-shaft is permitted to revolve only for dividing purposes. The entire movable head and parts attached are raised and lowered by a screw with a hand-wheel, which is graduated for accurate adjustment. The cutter is driven by a counter-shaft with a three- or four-step cone pulley, belted to a cone-stand on the floor, motion being given to the train of gearing driving the cutters by two universal joints with a slipping sleeve. This sleeve enables the cutter-slide to be placed in any position for either bevel- or worm-gears without affecting the length of the belts. For moving the cutter-slide in and out, motion is brought to its front part by means of a V-belt or light train of gearing from the traindriving cutter-arbor. The in-and-out motion is obtained by two clutches, one for feeding, which revolves at a slow speed, the return motion being much quicker. These clutches run loose upon the shaft, but between them is a single clutch, which has teeth on each side, and which slides back and forth between the opposite running clutches on a key or feather, fastened in the same shaft. Thus, as this central clutch is made to engage with one or the other of the clutches, a back or a forward motion is imparted to the feathered shaft, which is connected to the screw operating the cutter-slide.{br}
&nbsp &nbsp &nbsp The central clutch is automatically controlled by a system of levers and two adjustable buttons with opposite bevelled faces attached to the lower stationary slide, the levers and rollers being attached to the movable slide above. As the roller touches the bevelled button it throws the lever to one side, shifting the clutch and reversing the motion of the slide. When the roller comes to the oppositely bevelled button, the clutch is thrown to the opposite side and the motion is reversed as before. Means are provided to stop the feed at any desired point. There is a connection by a light chain between the cutter-slide and the stop-shaft cam and the trip. When the slide is withdrawing the cutter and the latter is out far enough to clear the edges of the blank wheel, the chain (which is adjustable) pulls the trip and allows the stop-shaft to make a revolution, then holds it stationary until another tooth is finished, when the slide again withdraws, releases the trip again, and so on until the wheel is completely cut, when the machine rings a bell, notifying the operator that the wheel is complete. The Working movements for cutting bevel-gears are the same as those described, the slides being raised to whatever incline is desired. For worm-gearing the slides are swivelled right or left, as required, in a horizontal position.{br}

<h1>Shears and Punching-machines</h1>
{br}[imageauto|Cutting Action of Shear|{UP}/Metal-Working Machines/PL 30 Fig 1-2.jpg]{br}
&nbsp &nbsp &nbsp Figure 1 illustrates the manner in which metal shears operate, a representing a piece of sheet iron and (s<sup>1</sup>) and (s<sup>2</sup>) two chisel-like tools (shear-blades), which are so forcibly moved toward each other that the edges penetrate and divide the iron. By giving to one blade the form of a ring (Fig. 2) and to the other that of a punch (s fitting into r) the shears become a punch and die, and the cut is circular. Shears are extensively used for trimming the edges of iron plates and sheets, while punching-machines serve for quickly making bolt and rivetholes, and also for working out irregular cuts.{br}

[imageauto|Adjustable Nippers|{UP}/Metal-Working Machines/PL 30 Fig 5.jpg]{br}
&nbsp &nbsp &nbsp In the ordinary cutting-pliers, which may be considered as precursors of shears, the two chisel-like blades do not move one past the other, and, as it is possible to bring only the edges in contact, the resulting cut surface is often somewhat uneven. In the nippers shown in Figure 5 the ordinary form is so far improved that by an adjusting-screw placed in one of the jaws the other jaw can be advanced only sufficiently to bring the edges almost in contact, thus preventing injury to the jaws.{br}

[imageauto|Rotary or Circular Shear|{UP}/Metal-Working Machines/PL 31 Fig 1.jpg]{br}
[imageauto|Duplex Lever Shear|{UP}/Metal-Working Machines/PL 31 Fig 2.jpg]{br}
&nbsp &nbsp &nbsp Shears generally have straight cutting-blades acting by rectilinear displacement (parallel shears, Fig. 4; Figs. 4, 5; Figs. 1, 2) or by rotation (lever shears). In the latter class two different arrangements can be made by the axis either running parallel or standing vertically to the blades. For executing long cuts without interruption the blades are given the shape of circular discs, with edges sliding over each other. Such rotary or circular shears are shown in Figure 1, in which both cutting-discs have positive motion. The blades are borne by two parallel shafts revolving in opposite directions, so that a piece of sheet iron—which must, however, not be too thick—introduced upon one side of the blades is delivered in two pieces upon the other side. That the iron be caught with requisite firmness the diameter of the blade must be at least eighty times the thickness of the sheet, so that, on account of the difficulty of constructing large steel discs, the application of this machineshear (which otherwise is mechanically complete) is limited to cutting thin sheets. Double-lever shears are shown in Figure 2. The two movable blades are screwed to a large trapeziform casting, which oscillates upon a bolt in the centre of the frame and receives on its upper end its motion by a circular eccentric working in a vertical slot. This eccentric is borne on a horizontal shaft, and by means of a pair of spur-wheels receives its motion from the fly-wheel shaft of a small steam-engine.{br}

[imageauto|Combined Lever Shear and Punching Machine|{UP}/Metal-Working Machines/PL 30 Fig 6.jpg]{br}
&nbsp &nbsp &nbsp Figure 6 represents a punching-machine combined with a lever shear. (A) is the fixed blade of the shear, (B) the movable blade, (C) the punch, and (D) the die; a represents the rotating axis of the lever(b), with which the movable blade of the shear as well as the punch is connected. The rotating axis bears on its outer end a pulley (c), upon which acts a heart-wheel (d) that vibrates the lever b. The heart-wheel (d) receives a slow rotation from a driving-shaft by means of gear-wheels (e,f). Upon this shaft, besides the fly-wheel (g), are the fast and loose pulleys (h<sup>1</sup>,h<sup>2</sup>), upon which the belt runs. The objection to such lever shears is that with straight-cutting blades the angle under which the edges catch the material to be cut is variable and at first may readily be so large as to cause the material to be displaced by the blades. The punch C is shiftable in a prismatic guide (K) of the frame, and is moved downward by the short elongation of the lever (b) over (a) and upward by two drawing-rods (i) so attached that they can be turned to both sides of the leverhead.{br}

[imageauto|Be Bergue's Combined Lever Shear and Punching Machine|{UP}/Metal-Working Machines/PL 31 Fig 3.jpg]{br}
&nbsp &nbsp &nbsp Figure 3 shows another combination of lever shear and punching-machine (De Bergue's). The movable shear-blade and the punch are, in a manner similar to that shown in Figure 2, secured to a trapeziform casting, which can be rotated about a horizontal axis and receives on its upper end a vibrating motion by means of a circular eccentric. This eccentric is keyed upon a hollow shaft enclosing the driving-shaft and receives a slow rotation by two pairs of gear-wheels. The fly-wheel shaft bears the driven pulley and gears through a pinion with the spur-gear shown in the front. This in turn drives the spur-gear which (shown at the back) vibrates the lever operating the shear and the punch.{br}

[imageauto|Whitworth's Parallel Shear with Attached Motor|{UP}/Metal-Working Machines/PL 30 Fig 4.jpg]{br}
&nbsp &nbsp &nbsp An equally good representative of the parallel type is Whitworth's large bar-iron shear (Fig. 4). (A) is the stationary lower blade, secured to a projection of the frame, and B the movable vertical blade, screwed to a carriage, which can be shifted in the prismatic guide a. The carriage is pushed up and down by the rod b from an eccentric on the front end of a horizontal shaft placed in the frame at (c). The back end of this shaft carries a large spur-wheel (d) meshing into a smaller one (e) upon the fly-wheel shaft of a special engine (k). This fly-wheel is designated by (f) and the crank by (g); h represents the slide-rod, (i) the piston-rod, (k) the steam-cylinder, (l) the sliding eccentric, (m) the eccentric-rod, (n) the valve-chest, and (o) the steam-admission steam-valve, which can be opened and shut by the hand-wheel (p). These shears are intended for use in rolling-mills, for cutting rolled puddle-bars into pieces for "piling" or reheating. On account of the varying resistance in cutting such bars, and to prevent disturbance in the working of other machines, it is advantageous to use a separate motor for working the shear.{br}

[imageauto|Parallel Shears for Boiler Plates|{UP}/Metal-Working Machines/PL 31 Fig 4.jpg]{br}
[imageauto|Parallel Shears for Boiler Plates|{UP}/Metal-Working Machines/PL 31 Fig 5.jpg]{br}
&nbsp &nbsp &nbsp The large shears for sheet iron shown on (Figs. 4, 5) are distinguished by the great length of the blades, by the use of which the edges of large plates can be trimmed at a single cut. For machines of this class a separate motor is usually provided. A special arrangement, shown in Figure 4, serves for quickly stopping the movable blade without stopping the engine and waiting for the heavy rotating masses to come to a standstill.{br}

[imageauto|Parallel Shears and Punching Machine|{UP}/Metal-Working Machines/PL 32 Fig 1.jpg]{br}
[imageauto|German Portable Parallel Shears and Punching Machine|{UP}/Metal-Working Machines/PL 32 Fig 2.jpg]{br}
&nbsp &nbsp &nbsp Figures 1 and 2 show two frequently-used combinations of parallel shears and punching-machines, one transportable, the other stationary. In Figure 2 the shear and the punch are placed one over the other and in Figure 1 opposite each other, while both are belt-driven. In Figure 1 the power applied to the live pulley e1 is transmitted through the pinion d to a spur-wheel {c), upon whose shaft is a second pinion (b), which in turn drives the large spur-wheel (a). The shaft of this wheel drives the punch (D) and the shear-blade (B); the fly-wheel (f) is to aid the belt in overcoming the resistance of the material to be punched or sheared. The frame is a hollow casting. Figure 2, which is a German portable punching and shearing-machine, may be operated by belt or hand-power. The same sliding piece carries at its lower end the punch and at its upper end the movable shear-blade. This machine has a truss frame.{br}

<h4>Hydraulic Punch</h4>
[imageauto|Hydraulic Punch|{UP}/Metal-Working Machines/PL 30 Fig 3.jpg]{br}
&nbsp &nbsp &nbsp In the hydraulic-machine (Fig. 3) the cutting-stroke of the punch is effected by a small force-pump (concealed in the framework and controlled by the upper hand-lever), conveying water or oil from a reservoir into a cylinder with its piston forming one piece with the punch. The up-stroke is effected, with the assistance of the lower hand-lever, after communication has been established between the cylinder and the reservoir. This arrangement is practically a combination hydraulic-press and punch. Shears may be classed as well under "Presses" as under any other head, as they operate by simple pressure.{br}

<h1>Metal-working Presses</h1>{br}

&nbsp &nbsp &nbsp These presses do their work by pressure, which, whether exerted gradually or instantaneously, has the same effect as regards the energy applied, although sometimes, on account of the inertia of the material, there is an unequal distribution of that energy.{br}

[imageauto|Blacksmth's Hammer and Anvil|{UP}/Metal-Working Machines/PL 32 Fig 3.jpg]{br}
&nbsp &nbsp &nbsp The blacksmith's hammer as it shapes the iron on the anvil (Fig. 3) is a primitive form of press; but if a pair of upright guides were attached to the anvil, restricting the hammer to a vertical motion, it would approach more nearly to the machine generally known as a press, and, in fact, would represent a class called "drop-presses" (Fig. 4). While there are numerous styles of presses adapted for punching, shearing, and forming sheetor bar-metal and other materials, they all contain the parts represented by the anvil or "bed," the hammer or "ram," and the guides or "slidebearings." The bed and the slide-bearings are always at right angles to each other, and usually form part of the same casting, called the "frame."{br}

<h4>Drop-press</h4>
[imageauto|Drop Press|{UP}/Metal-Working Machines/PL 32 Fig 4.jpg]{br}
&nbsp &nbsp &nbsp In a drop-press (Fig. 4) the ram, after being lifted to a certain height, is allowed to descend by gravity, the amount of work produced depending on the height of the fall and the weight of the ram. In doing work which requires sudden pressure, such as is given by a sledgehammer, the drop-press or its equivalent is indispensable, but in most cases gradual pressure is required.{br}

<h4>Power-presses</h4>
[imageauto|Power Press|{UP}/Metal-Working Machines/PL 32 Fig 5.jpg]{br}
[imageauto|Foot Press|{UP}/Metal-Working Machines/PL 32 Fig 7.jpg]{br}
&nbsp &nbsp &nbsp In a "power-press" this gradual pressure is usually obtained by using a fly-wheel connected with the ram by an intervening shaft, crank, and pitman (Fig. 5), and in a foot-press it is got by the intervention of a series of levers and their connections between the foot and the ram (Fig. 7). In most power-presses the fly-wheel revolves loosely on the shaft, to which motion is given—only when connected with the wheel—by a "clutch," which device is generally a pin that slides in a projection on the shaft and is capable of being moved out by a spring until it engages with a notch in the hub of the wheel. Most clutches are "tripped," or caused to engage with the revolving wheel, by a treadle and a rod connected to a wedge or other device which by the action of the press itself has previously locked the clutch-pin out of gear with the wheel. The depression of the treadle unlocks this device and allows the pin to re-enter the wheel for another stroke. Press-clutches are usually thus made automatic—that is, they are so constructed as to throw the fly-wheel "out of gear" with the shaft at the completion of one revolution of the wheel, and the consequent completion of a stroke of the press. The clutch being operated by a treadle, the operator's hands are left free to handle the work.{br}
&nbsp &nbsp &nbsp The usual method of obtaining rectilinear ram motion from rotary shaft motion is by means of a crank or an eccentric on the shaft, which revolves in the head of a pitman connected with the ram. An advantage of this form is that the eccentric not only forces the ram down, but also draws it up, ready for another stroke. The amount of stroke (or distance the ram is caused to move) will, of course, depend on the amount of the eccentricity. The same effect may be produced by cams on the shaft bearing against rollers on the top of the ram, the ram being forced away from the shaft by the cams and drawn back to its original position by other means, such as springs, weights, or return-cams.{br}

<h4>Toggle Coining-Press</h4>
[imageauto|Coining Press|{UP}/Metal-Working Machines/PL 33 Fig 1.jpg]{br}
&nbsp &nbsp &nbsp When a small amount of motion and a consequent increase of pressure are desirable, the rectilinear motion can be produced by a toggle, which, on account of the nearly irresistible pressure exerted at the end of the stroke just when such a pressure is most required, is almost universally employed for coining-presses. Such a toggle is usually opened and closed by a crank motion. Coining-presses, (Fig. 1) usually have two massive columns, joined at the bottom by the bed and at the top by a trussed cross-beam, the columns being as close together as practicable, in order to get as much rigidity as possible.{br}

<h4>Screw-press</h4>
[imageauto|Adjustable Screw Press|{UP}/Metal-Working Machines/PL 32 Fig 6.jpg]{br}
&nbsp &nbsp &nbsp The principle of the screw is frequently used in presses to transform rotary into rectilinear motion. In this type the nut in which the screw works is a part of the frame, the end of the screw bearing against the ram (Fig. 6). This is also an effective form of press for certain kinds of work, but it is now rarely used except for hand-power.{br}

<h4>Drawing and Punching-presses </h4>
[imageauto|Open Fron Draw Press|{UP}/Metal-Working Machines/PL 32 Fig 8.jpg]{br}
&nbsp &nbsp &nbsp The shape and size of a press depend on the work for which it is designed. A press for cutting out large sheetmetal blanks, such as sections of "pieced" tinware, requires a well-spreadout frame with a large bed, containing a hole of generous proportions, through which may drop the sections cut in the dies (Fig. 8).{br}

[imageauto|Back Wheel Punching Press|{UP}/Metal-Working Machines/PL 32 Fig 9.jpg]{br}
&nbsp &nbsp &nbsp On the contrary, a press for punching out nuts (Fig. 9), for shearing heavy bar-iron, or for other work which requires a heavy stress in a small space, must be compact, with a large reserve of metal in the frame, not only to withstand a breaking strain, but also to prevent any flexure of the parts, or, as it is called, "springing." Even if a press which springs open appreciably at every stroke should produce good work for a time, disintegration at the weakest point gradually goes on and will sooner or later make trouble. For this reason, if for no other, a properly proportioned press-frame, with interior angles well filleted and with exterior angles neatly rounded, is always to be preferred, even if considerations of beauty are left out of the question. Presses for long and narrow work, such as buggy-axles, should have two or more pitmans to transmit the power from the rotating shaft to the ram. Where there are only two pitmans they should be placed near the upright columns, to obviate springing in the shaft, and the ram and the bed should be well trussed, to prevent springing. Presses for work that is cut and formed or formed only, such as tea-trays, fruit-can tops and bottoms, etc., are usually inclinable, so that the work pressed to shape in the dies may be raised out of the lower die by spring knock-outs, and be allowed to slide back by gravity through an opening in the back of the press. A style of press usually adopted for heavy punching and shearing has the shaft running from front to back, the front end of the shaft being turned into a crank-pin, while the fly-wheel is at the back, out of the way (Fig. 9).{br}

[imageauto|Drawing Press|{UP}/Metal-Working Machines/PL 32 Fig 7.jpg]{br}
[imageauto|Open Front Draw Press|{UP}/Metal-Working Machines/PL 32 Fig 8.jpg]{br}
[imageauto|Double Action Power Drawing Press|{UP}/Metal-Working Machines/PL 33 Fig 2.jpg]{br}
&nbsp &nbsp &nbsp For work in comparatively thin sheet-metals the form having the shaft running from side to side is preferred (Figs. 7-9 ; Fig 2).{br}

<h4>The "Bottom-Slide" Press</h4>
[imageauto|Bottom-Slide Press|{UP}/Metal-Working Machines/PL 33 Fig 3.jpg]{br}
&nbsp &nbsp &nbsp This press (Fig. 3) possesses several advantages. It has a heavy base supporting the shaft or shafts, gearing, fly-wheel, etc., while columns of considerable tensile strength support a trussed head. The ram is guided by the columns, is given an upward motion by cams on the shaft, and returns by its own weight, thus obviating the necessity of an expensive lifting arrangement. This press is adapted for deep drawn-work. It economizes metal, which is massed in and around the base of the machine.{br}
nbsp &nbsp &nbsp Although the ram is made in many forms, its adjustment, which is an important feature, usually depends on the screw principle in some shape, but eccentrics, wedges, and other devices are also used. In some presses the bed is capable of. adjustment, by which considerable latitude is possible between the bed and the ram; but this often affects the rigidity and accuracy of the press. The complexity of presses increases in accordance with the increase of the complexity of the work to be produced. Deep or drawn work, such as seamless cups and pans, not only is cut out but also is drawn to shape by a single stroke of a double-action press. Such presses contain two rams, one inside the other, so arranged that when the work of one is completed it is taken up and finished by the other. Triple presses are also in use. By multiplying the cams on the press-shaft the number of operations possible in a single revolution of the shaft is also multiplied..{br}
nbsp &nbsp &nbsp The variety of articles produced in presses and dies is constantly increasing. The cheapness of household utensils testifies to the value of the machines by which they are made. Sheet-metal vessels, bells, lamps, and fancy goods of all descriptions, are sold at prices so close to the value of the raw material that the casual observer is at a loss to understand how they can be made for the money. To illustrate the almost boundless capacity of this class of machines it may be mentioned that a press fitted with gang-dies and operated by one man will cut and draw to shape in ten hours two hundred and eighty thousand brass cartridge-cups and will turn out lamp-burner caps nearly as fast. The user of such articles has his wonder at their apparent cheapness turned to indignation when he learns that the retail vender asks a price so much above their first cost.{br}

<h1>Power-hammers</h1>{br}
&nbsp &nbsp &nbsp  While not usually classed among machine-tools or metal-working machinery, bear a prominent part in the work of the modern machine-shop. They are used on masses of metal (generally malleable iron or steel, usually worked in a hot condition) for the purpose of increasing their density, changing their form, or improving their finish. By them pasty material is worked to close up its pores and to drive out the gases and the slag; they are employed to reduce large thick masses to comparatively thin plates, to build up several thicknesses into one block, to finish objects already roughed out by other hammers or by rolls, to bend and shape pieces to desired forms, and to weld together separate lengths and shapes. The weight of blow given by hammers varies from a few pounds to a hundred tons. The weight, or hammer proper (also called the tup, or the ram, and sometimes the monkey, when free), may be attached to a helve or to a piston-rod, or it may be raised and let go free, as in a piledriver, and it may strike either "dead" or "cushioned" blows.{br}

<h4>Helve-hammers</h4>
[imageauto|Bradley Helve Hammer|{UP}/Metal-Working Machines/PL 33 Fig 5.jpg]{br}
&nbsp &nbsp &nbsp The blows of helve-hammers simulate those given by a sledge wielded by the human arm, the helve giving an elasticity desirable in some kinds of work. This effect may be increased by the use of springs. The helve may be raised by a cam or by any other mechanical device permitting rapid release, or, as in Figure 5, it may be worked by a crank, from whose control it never escapes.{br}

<h4>Drop-hammer</h4>
[imageauto|Pratt and Whitney Drop Hammer|{UP}/Metal-Working Machines/PL 33 Fig 6.jpg]{br}
&nbsp &nbsp &nbsp Between the drop-hammer and the drop-press there is little difference. One form (Fig. 6) has the weight or hammer attached to the end of a wide board, which is raised by being gripped between two rapidly-revolving rollers, and is then released by the rollers being so far separated that they no longer act upon the board by friction. In another form the weight is raised by a rope wound up by friction rollers and then released.{br}

<h4>Crank-hammer</h4>
[imageauto|Shaw's Crank Hammer|{UP}/Metal-Working Machines/PL 33 Fig 8.jpg]{br}
&nbsp &nbsp &nbsp One form of crank-hammer (Fig. 8) has between the cross-head (which is driven by a connecting-rod attached to a crank) and the weight a strong spring of leather bands, thus giving a cushioned blow.{br}

<h4>Steam-hammers</h4>
&nbsp &nbsp &nbsp Some steam-hammers have the weight attached to the rod of a piston raised by live steam, which is allowed to exhaust freely, thus causing the piston and the hammer-head to drop by their own weight. In this type the blow may be "dead," or it may be cushioned by the exhaust being closed at a certain point, so that the steam is compressed in the lower end of the cylinder. In another type of steam-hammer the piston to which the hammer is attached not only is raised by steam, but also is driven down by the same agent, thus striking the work with a force due not only to the weight of the piston and the hammer-head, but also to the steam-pressure. The blow may be cushioned or not, at the will of the operator, who can compress the exhaust at any point in the stroke. The anvil may be carried by the same frame as the rest of the machine, or, as is best in large sizes, may have a separate foundation.{br}
&nbsp &nbsp &nbsp For forging metal into irregular shapes, such as cranks, marine rudders, locomotive rocker-arms, and pedestal-frames, an extra long stroke is required. For axles, trunk-bars, engine-frames, and for stamping work in forms, there is needed an extra width at the height of the anvil. Small machines have single standards or uprights; large machines with a very heavy hammer and striking a very strong blow have double uprights, which may be divided, for convenience in working, either from the front or from the side.{br}

[imageauto|Power Hammer with Single Standard|{UP}/Metal-Working Machines/PL 33 Fig 4.jpg]{br}
[imageauto|Seller's Power Hammer with Double Standard|{UP}/Metal-Working Machines/PL 33 Fig 7.jpg]{br}
&nbsp &nbsp &nbsp Figure 4, shows a 350-pound hammer with a single standard; Figure 7, a 2¼-ton machine with double standard. For convenience in finishing work it is now customary to place the ram or "tup" (terms applied to the hammer-head) and the anvil diagonally in relation to the single upright. 49&nbsp &nbsp &nbsp This diagonal position permits long frames to be handled freely in either direction.{br}
&nbsp &nbsp &nbsp When steam is taken on the top, the machine may also be used as a squeezer or vise for holding work in hand-swaging, etc. Small hammers are generally arranged not only to take steam on both sides of the piston, but also to work automatically any number of strokes. Very large machines do not usually work automatically. Some machines have a supplemental valve for throttling the exhaust below the piston, but permit free exhaust above the piston—an arrangement which enables the blow to be diminished in intensity without materially decreasing the rapidity of motion. It is an advantage to have the exhaust-nozzle, with the drip-pan, so arranged that there may be used a large exhaust-pipe detached from the valve and carried by the roof, thus giving an exhaust free from back pressure, and enabling the water from the condensed steam to be readily carried off from the drip-pan to any convenient place below.{br}
&nbsp &nbsp &nbsp The precision with which steam-hammers operate is no less wonderful than the wide range of force with which they may be made to work and the titanic energy which the greatest of them exert. Some hammers which are capable of striking a blow of from fifty to one hundred tons are so accurate in their adjustment that they may be made to crack a walnut or may be brought down, without breaking the delicate crystal, to within a small fraction of an inch above the face of a watch placed upon the anvil.{br}

<h1>Tendencies in Metal-working Machinery</h1>{br}

&nbsp &nbsp &nbsp The tendency of manufacturers of metal-working machinery in general, and machine-tools in particular, is in two lines, leading from the previous direction of thought and work. Two distinct classes of machines are becoming more and more common each year: special tools for effecting from one to twenty operations at a time upon one article, where such article is manufactured in large quantities, and what might be called "universal" machines, having a wide range of adjustment and being capable of doing many kinds of work. Of the universal machines, the boring- and turning-mill previously mentioned is a good type, an important variant being a machine which not only bores and turns the cylindrical surfaces of large cylinders, but also planes their flanges, faces-off their valve-seats, and drills boltholes in flanges and seats without removing the cylinder from the machine, and with little if any change of place while being worked. Such a machine has a wide range in the dimensions of cylinders which it takes in and in the arrangement of their parts; in this respect it differs greatly from the special machine proper, which is intended to take in one or more articles at a time, but permits of little if any variation in design, construction, dimension, or finish in the articles produced.{br}
&nbsp &nbsp &nbsp The modern machine-tool is an instrument of precision, and its work is characterized by its greatly increasing accuracy and finish. The increasing exactitude of lead-screws and index-plates, due to the loving and intelligent labors of a few master minds in machine-tool building, has induced an increasing degree of accuracy in all other machine-tools and in all machines built thereby; and the standard having been thus raised, the demand has gone out from machine-builders for a higher grade of workmanship in all their machine-tools and metal-working machinery, so that all along the line, from bloom-squeezer and steam-hammer to delicate milling-machine and gear-cutter, the grade has been improved. Thus do demand and supply, desire and its fulfilment, go hand in hand, opening and smoothing the way of human progress.{br}
&nbsp &nbsp &nbsp It is to be regretted that the wide range of operations and the wonderful accuracy of modern machine-tools have done so much to lower the standard of personal dexterity in mechanical manipulations. The millingmachine and the emery-wheel have nearly supplanted the wonderful skill once exercised by the file and the scraper. The machinist is lapsing into a specialist, able to operate but one class of machines and to do but one class of work, and the working force of the machine-shop has become merely an assemblage of machine-tenders.

<h3>Information Sources</h3>
<ul>
<li> <cite>The Iconographic Encyclopædia Vol 6, Applied Mechanics</cite> by Robert Grimshaw, 1890 pages 101-134 </li>
</ul>
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