By: David Eisan
I have written this for the total novice, so pros, please just skip over this and don't flame me for pointing out the obvious.
For a few years I had a Delta 37-190, a 6" 3/4 hp jointer. I had a few problems with it. Namely getting the tables level, setting the knives and getting a straight edge/flat board. After a lot of seat of the pants learning I figured out how to make the little jointer sing and get boards perfectly flat.
Please everyone, unplug your tools before working on them.
All jointers have the tables installed, and then they are surface ground or milled in place, they should be flat. But due to the price driven offshore manufacturing, by the time you get your jointer, like wood, cast iron moves. Cast iron is not seasoned (left alone to stabilize for a period of time) before milling like it used to be. Also, older/used jointers may be worn, or improperly used/treated requiring tune up.
1 - Check for table flatness
A Starrett 8' 0.0001" flat straight edge is not required. I use a 40" Lee Valley straight edge and a set of automotive feeler gauges to check jointer beds for flatness. I remove the cutterhead guard, move the fence to the rear position and roll the cutterhead to a position where no knives poke out and raise the infeed table. I lay the straight edge across the infeed and outfeed tables checking, front, center, back and both diagonals for flatness. You may have to raise/lower the tables to get them both in the same plane. Try to slip a .007" feeler gauge under the end of the straight edge as a go/nogo gauge. If All checks out, your tables are flat, if not, you need to make them flat. I use 0.010" as my personal tolerance flatness, I don't know any manufactures published specs. You may want better, or you may be willing to settle for less. You decide.
2 - Make your tables co-planer
The tables need to be in the same plane (i.e., flat). Sometimes tables can be made flat by just taking up play in the dovetailed ways. You should not have tight or loose tables, they should slide freely/smoothly without you having to exert major force. They should also not flop around. This is very subjective. If it jerks as you raise lower it, that's too tight. If with the jointer running and the tables unlocked, they lower, that is too loose. The tables are tightened/loosened with gib screws against dovetailed ways. There are usually two or three allen screws with bolts around then on the back side of both the infeed and outfeed tables of most jointers. These screws push against a bar that takes up play in the dovetailed ways of your jointer tables. Back off the bolt surrounding the allen screw and tighten/loosen various screws while testing the up/down movement of the table until you have all the screws adjusted just right and the table moves smoothly. By applying more pressure at higher screws you can raise the tables, at lower screws, you can pull the table down. These are all tiny adjustments. If your tables truly droop, your only solution is having them re-ground, or shimming them level.
3 - Shimming drooping tables level
Go buy a second set of automotive feeler gauges. Since you move the infeed table frequently, that is not the one to shim, it is common practice to shim the outfeed table. Loosen off the gib screws so you can slide various feeler gauges up into the dovetailed ways, one per side. Start at 0.001, tighten the gib screws back down and see if that raised the table enough. I find this a two person job, one person lifts up on the outfeed table, the other slips the feeler gauges into the dovetailed ways. Go up one thou at a time until your tables are co-planer/flat. Once you have the correct shims, break them off in the dovetailed ways. You now have two feeler gauge sets missing one gauge each. Note: Do not borrow the feeler gauges to do this, your brother will not be happy about this. Don't ask me how I know this.
4 - Fixing 'raised' tables
I have never come across this, but I guess simply loosening the upper gib screws to allow the tables to droop should work.
5 - Finding highest knife and setting outfeed table¶
I have yet to see a jointer from the factory with all knives within a few thou of each other. This makes for one knife doing all the work and a really scalloped looking cut. Most jointers come with truly crappy wrenches, toss them, get a decent wrench. I set my knives by hand with a known flat aluminum 12" speed square. (I adhered 220 grit paper to my jointer bed and lapped the wide edge perfectly flat.) You will also need to have your shop really quite, no radio on, no kids screaming and a good ear. First I find the highest knife. Lower the infeed table all the way to get it out of the way. I lay the square 90% on the out feed table so it just hang over the knives on the cutterhead. Rotate the cutter head to find which knife moves the square the most. Raise the outfeed table in real small increments until the square no longer moves while you roll the cutter head back and fourth by hand. You should hear the HSS blade scrape on the aluminum, but the square should not move. If all of your knives are high, do the reverse lowering the table until at the same level as the highest knife.
6 - Setting individual knives to outfeed table
I have only set knives on jointers with jack screws, so those of you without them, sorry, I cannot help you. Slightly loosen off the nuts around the pressure screws on the next knife. With the allen key in the jack screw, rotate the cutter head back and fourth, turn the allen key clockwise, until you hear the slight scraping sound. If the aluminum square moves, the knife is too high, back the jack screw off and tap the knife back down with a block of wood and try again. When one side is at the correct height, remove the allen key. Get a scrap of hard wood, place it from the infeed table over the knife, but so you can see the bolt to tighten that side down. Lean on the scrap of wood, tighten the bolt down. Without leaning on the scrap block of wood you will get bolt creep, and the knife will raise up. This bolt creep can drive a person totally insane when setting knives. When you have done both edges of the knife, tighten down the center bolts. Don't reef on the bolts, you will strip them. Test to see that you were successful by again rolling the cutterhead and listening at both the front and back edge of the knife, you should hear a scrape, but the aluminum square should not move. If you blew it, try again. Do this to both other knives, and even the first one if one side was higher than the other. The first time I did this, it took me three hours to set my knives, but I wasn't restricting bolt creep by leaning on a block of wood on the knife either, it took more frustration for me to figure that trick out. I can now set three knives by hand in under 15 minutes. You too can learn how to do this.
Your jointer should now be in perfect tune.
You do any of this at your own risk, I am not responsible for any of your actions. This is just me relating personal experience and is not meant as professional instruction. If you do not feel confidant doing any of this, please refrain from doing so.