Back to Crescent Jointers main pageThe Crescent Safety Head for Jointers
The following excerpt is from the 1910 Crescent catalog Crescent Round Safety Head for Jointers |
A cutter head of cylindrical shape, such as is shown in our illustration, is appropriately called a Safety Head, as distinguished from the common type of square head. The main advantage is that they are safer to the operator. In case of a hand getting in contact with the knives on a Safety Head, a flesh wound would be about the limit of the injury; while with a square head the hand is usually drawn in, resulting in the loss of fingers or part of the hand. It is to minimize the extent of the injury that the Safety Head is recommended.
In the Crescent Safety Head a thin, narrow knife is used, which is held in place by a heavy steel throat-piece clamped firmly into position by a number of key-plugs placed at intervals in sockets drilled into the body of the head. Each of these key-plugs is cylindrical in shape, having a flat place milled off on its side, making it wedge-shaped. A hollow set screw passes through the center of the key-plug, bearing against the bottom of the socket, thrusts the key-plug outward on its taper, causing it to key tightly and evenly against the throat-piece, thus holding the knife very firmly over its entire width. A very slight tightening of the screws, with the combined wedging action of the key-plugs, is sufficient to hold the knife firmly.
There is no tensile strain on the screws, as is the case with other forms of construction, but by our method the danger of accident arising from broken screws is entirely eliminated. The small end of each key-plug is placed outward, so that a key-plug could not fly out even if the screw were loosened, but would tend to tighten from its own centrifugal force. Neither can a throat-piece fly out, as it has a tongue along its lower edge fitting into a groove milled in the head. The knife is firmly supported by the solid metal of the head on its entire back surface, close out to the cutting line. The space in front of the knife is completely filled by the throat-piece, so there is no possible chance for chips to drive under the knife, thus overcoming another common source of danger.
Another advantage of the Crescent Safety Head is, that it is stiffer than a square head of same cutting circle; because it is of greater sectional area. This makes a steadier running head, less tendency to vibrate, and less liable to get out of balance. The bearings and body of each head are ground absolutely true.
The Crescent Safety Head for Jointers
Special Knives for molding, beading and grooving can readily be used. For this purpose two short sections of special throat-pieces are furnished. These are made of correct thickness to admit special cutters ¼ inch in thickness. An important feature of the Crescent Safety Head is the method employed for setting the knives correctly. A special key wrench is inserted into a hole, back from the knife. A lip on the end of the wrench projects under the lower edge of the knife, and by turning the wrench slightly, the knife is brought forward accurately, as far as desired; a small gauge being furnished to indicate when knife is in correct position. The knives are to be but lightly clamped while being set to correct position, then when set, are to be firmly clamped by tightening up on the key-plugs. With this arrangement it is as easy to set the knives on this round head as on the common square head.
All Crescent Safety Heads of 4¼ -inch cutting circle, or over. will be made with four knives. This applies for the 12, 16, 18, 20 and 24-inch Crescent Jointers. All heads of less than 4¼-inch cutting circle will be made with two knives only. This applies for the 8-inch Crescent Jointers and the Variety Wood-workers. Same rule applies for Safety Heads made to order to fit other makes of Jointers.
In a four-knife head the work may be fed much faster than when but two knives are used, and yet produce as good results, if knives are properly set to give each knife an equal cut. Or if it is desired to use but two of the knives, then the other two may be taken out and laid aside for reserve, and their place in the head filled with a hardwood strip of same thickness as knives.
The knives furnished with these heads are a very fine grade of self-hardening high-speed steel. These are much better than the common carbon steel knives, as they hold an edge much longer. The knives are ⅛ inch thick, 1⅛ inches wide.
The Crescent Safety Head can be furnished with any size of Crescent Jointer, at a slight advance in price over the common square head. Or they can be furnished for machines of other makes when full dimensions are given: a diagram blank for this purpose will be furnished on application.
With each head is furnished one set of knives (two or four according to size of head), one special wrench for the hollow set-screws, one key-wrench for adjusting the knives, one gauge for setting knives, and two short sections of special throat-pieces for holding special cutters.
Directions for taking knives out of a Crescent Safety Head
Knife Setting
First loosen the hollow set screws that, pass through the center of the key-plugs, by Riving about a half-turn to the left with the hexagon wrench sent along for that purpose. Before taking wrench out, strike a blow on top end of wrench with a light hammer to release the key-plug from its wedged position in the head. The key-plugs are wedge shape with their thick end toward center of head, therefore have to be driven a blow downward toward center of head to loosen, after screw is released. When all the key-plugs are thus released, then the knife will be free and can readily be removed. After knife is removed, the throat-piece and key-plugs can also be removed. To replace the knife, first see that all the dirt and dust is removed from the knife seat and throat-piece. See that each key-plug is in its proper place according to the numbers stamped on the same. After the key-plugs, throat-piece and knife are properly placed, then tighten the key-plugs very lightly; then adjust the knife to cutting position by use of the special wrench inserted into the holes at back of knife. Use the small gauge furnished, with end of screw over top of the edge of knife to get a uniform setting of the knife edge. When knife is properly set, then tighten the key-plugs snugly, ready for use.