I’ve been setting up my jointer, and I have a question.
How tight do you guys hold tolerances on jointer blades?
I’ve set them up as close as I can, but “as close as I can” seems to be +- .002 across a blade, as measured by a dial indicator.
I suppose I can keep chasing those last two thousandths, but damn, Skippy…
Replies
If your blades aren't straight, you may be able to get the ends set equally but there can be a difference in the middle. .002" is quite a bit. Grinding doesn't always result in straight knives, it can tail off on the ends. You can end up with visible knife marks. Cutterheads with screw adjusters are easier than those with just springs under the knives, .002" can be little more than a breath of movement. Do the best you can then do some test cuts. If the cuts don't meet your expectations, try again.
Makes Sense
The blades (and machine) are new.
I cut about 20 feet, then realized it needed to be lubed and adjusted.
I'm following the procedures in John White's book, but he doesn't mention how close is close enough for jointer blades, which leads me to believe they need to be right on.
The machine is a Grizzly, an 8" jointer. Doesn't have a gib on the outfeed table, but it does have what I've learned are called "jack screws" under the blades.
I'll work on it some more, but this is a pain in neck!
I have a grizzly 8"
I've got a grizzly jointer as well, and it can be a little tedious to setup. I begin by using the knife alignment jig included with the machine (they will sell you one if you don't have one). It rests on the cutterhead cylinder and pushes the blade down to a set distance against the springs. Hold it down HARD and tighten the middle three screws so they're fairly snug. Then shift it down and tighten the front screw, saving the back screw for later. Do this to all the blades, then gradually tighten them all in multiple revolutions, again leaving out the back screws. When everything else is tight, check with the alignment tool to make sure nothing shifted; if they did the guide will rock back and forth just slightly. If everything's good, then go back and slowly tighten the rear screws until they're tight and check them again. It may sound like a strange method, but it's the only way I've ever gotten the knives to stay put while tightening, and even then sometimes I have to go back and adjust one afterwards. When everything's all tightened up I grab my machinists straightedge and lay it on the outfeed table over the cutterhead. Slowly rotate the head until each blade passes through Top Dead Center. As they pass TDC they should gently contact the straightedge and nudge it forwards maybe 1/8" or so. Often they will each move it a slighty different distance since they're either slightly off or the edges arent 'quite' straight. Check the back, middle, and front to see what they're doing and adjust the outfeed table until you find a happy medium. Usually I'll have three blades making contact with one a little low and not necessarily the same ones all the way across. The nice thing about having 4 blades is things kindof tend to average out between them, just make sure one isn't protruding exceptionally far. We're talking about differences of .001" or less on this even though it feels like a lot. Eventually you just have to call it good and run a test piece. You'll know pretty quick if things aren't working out. Good luck to you - I personally hate this particular aspect of woodworking and have always regretted not getting one of those carbide square deals. :-P
No springs in this jointer, but thanks for the advice.
Gibs are the bars that hold the knives in place in the cutterhead. With jack screws, you insert the knives, get them in position then lightly tighten the gib bolts and make sure everything is seated properly. Back off the screws so the knives can move but not so much they are too loose. Use the jack screws to lift/raise the knives. If you go too much, back off those jack screws and push the knives back in with a hardwood block. Eventually you will get to the point when a slight turn on a jack screw will be too much. This is when it can get frustrating, you may go too much, then too little a few times. If the gib bolts are too tight, the jack screws won't respond smoothly. Ideally, you want the knives to be exact, 0.000", however, ground knives, new or not, may not be perfectly straight and even. You should be able to get the ends set but there may be a difference in the center because of this.
Once you get the knives set as close as possible, do some test cuts. I advise against trying to set the jointer for whisper light cuts. It puts a lot of stress on just the very tips of the knives. Work pieces ride up when jointing and there's nothing you can do about it. It only shows if you make several passes on a parallel edged work piece. You will find that after several careful passes, the board will not be the same width. With correct jointer feeding technique, the leading edge will be less, with incorrect technique the trailing edge will be less. It happens at any depth setting but more so with a vey light cut, 1/32" or less. Since you are stressing just the very tip, the blades dull quickly and results get worse.
Set for 1/16" to test. If you have it correct, you should not see any knife marks on the edge of your work piece, hold it up to the light, get out the magnifying glass and you still won't see any marks. This will tell you if everything from knives to tables as well as your technique and feed speed are correct. If you aren't getting this result, something isn't right. When everything is right, your jointer will be a marvelous machine, producing absolutely straight edges with no machine marks. Of course, it won't stay that way forever. The jointer is a really simple machine but very sensitive to the slightest set up or technique error. Set up can be a pain the first 12-20 times, sometimes you need to walk away for a minute. Stay calm and persevere, you'll get it.
One
I think I have one blade set. After several hours.
I'm going to go out, get in the left lane of the interstate, and drive a mile and half below the speed limit.
Sometimes, it's the only thing that makes me feel better.
The comment on using a straight edge to set the blade heights describes the best procedure in my experience. When the blades all just jostle the straight edge as they pass top dead center, the setup is done.
Planer blades can be set to a constant cutting circle using a crowfoot gauge off the cutterhead--the old millmen got great results with just a screw tip, no dial indicator, on these-- but a jointer needs to be set to the plane of the outfeed table, not to a cutting circle. In either case, it is important to note that very fine precision is achieved with the geometry of circles and straight lines, not numbers. There are times and places for tramming with an indicator, but in this case I think it will just mislead you.
It is not a good idea to set knives in any cutter head one at a time. Tightening the gib screws has to be done working around the head, not across it. Tightening all the screws on one knife while the others are loose will distort the head, and tighening the screws on the second knife will distort it again.
Going to have to research a crowfoot gauge.
I'm a carpenter by trade, and quite new to all machinist work. So I've never heard of a crowfoot gauge, and don't know how to use one.
Thanks for the concept of tightening around the head-- the way I was using was to keep all the blades tight except the one I was working on, set it, tighten it, and then go to the next one.
Since it never occurred to me that tightening the second one could move the first one, I simply didn't go back and check. Ignorance, this is Bliss, come in, please...
P.S.-- oh, I see. You're saying NOT to use a crowfoot, because it's the plane of the table that counts, not the circle.
P.P.S-- Gotta look up "tramming", don't know what it is, either. :)
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