setting jointer knives - importance of top dead center

[Marc Rochkind]

I have a jig with magnets that I got from Grizzly that's almost foolproof, in that it sticks hard to the outfeed table and magnetically draws the knives up so they can be tightened.

The "almost" is that the rig depends on scribing a line on the fence at top-dead-center, and to find that you have to use a piece of wood and roll the knife assembly back and forth until you judge the knife to be at top-dead-center.

That seems to me to be difficult to do precisely. I think I did it as well as I could, but it could be a few thousandths off.

So, the question is: How important is it that that scribed line be EXACTLY at top-dead-center?

Any tricks for getting it exactly there?

[Darcy Warner]

Does it really matter that much? You can always adjust outfeed up and down to compensate.

[Marc Rochkind]

[True, you can adjust the outfeed height. But I believe that also depends on finding top-dead-center.]

See my later reply. Darcy is quite right.

[Ole Anderson]

I am no expert, I am sure some will chime in though. I use a light 12" straight edge, not magnetized as when I roll the knife assembly forward I want to gauge how far each knife pulls the straightedge forward. I want the knife sitting a few thousandths proud of the out feed table and if the knife pulls the straight edge evenly at each end of each of the knives about an eighth of an inch, I am happy. I am sure there are expensive ways to make it more accurate, but this method works for me. Top dead center would be when the knife pulls the straightedge forward 1/16".

[Mel Fulks]

Marc, I suggest you read the current thread ,also in this forum. It's "What is My Issue? Jointer help"

[Marc Rochkind]

Does it really matter that much? You can always adjust outfeed up and down to compensate.

Thanks, Darcy... adjusting the outfeed table turns out to be very easy. Now that I think about it, kinves have to be straight and all at the same height, which the jig ensures. If that height isn't exactly TDC, outfeed table can make up the difference.

[Darcy Warner]

I am no expert, I am sure some will chime in though. I use a light 12" straight edge, not magnetized as when I roll the knife assembly forward I want to gauge how far each knife pulls the straightedge forward. I want the knife sitting a few thousandths proud of the out feed table and if the knife pulls the straight edge evenly at each end of each of the knives about an eighth of an inch, I am happy. I am sure there are expensive ways to make it more accurate, but this method works for me. Top dead center would be when the knife pulls the straightedge forward 1/16".I set knives in my 30" jointer with a short board with two pencil marks. Roll head, make sure knife pulls board to second mark and I am good.

[Martin Wasner]

That's pretty much exactly how I do it. I use a piece of aluminum with a couple of marks.

I hate setting the knives on my 12" jointer, I really need to get a tersa head for that thing. The 6" Grizomatic is a cakewalk with jack screws.

[Tom M King]

The trick is being able to tighten the screws just enough to hold the knife in any place, but still be able to slide it. I take any springs, and jack screws out. A thin strip of Boxwood about 5 or 6 inches long always has it's end on the outfeed table touching the table. Using the strip of wood, push the knife down on both ends while swinging the head back and forth with a wrench on one of the middle screws. When you feel the knife rubbing the hard strip of wood, but not pushing it up off the outfeed table, tighten the screw that the wrench is on. Then tighten the other screws. It might take 20 seconds per knife.

I do the same with power planers.

Learn to feel how tight is right on the end screws. You just take the slack out, but no tightening. If you lift the end of the strip of wood on the outfeed table, you will push the knife down too far. If that end of the strip of wood stays in contact with the outfeed table, it's impossible to push the knife too low, unless you go too fast, but then you can just lift the knife back up, and go again.

[Bruce Wrenn]

To find TDC, raise both tables to the same height. Then using a scrap with a nail or screw projecting about 1/8" , with screw / nail down, place it on either table. Bring forward till screw /nail contacts head, then put a mark on fence with a pencil. Now do same thing on other table. Split the distance between two marks, and that's TDC. Lifted from John White's book "Care and Repair of Shop Machines."

[Martin Wasner]

I take any springs, and jack screws out.

Mine uses springs. I've debated about taking them out. They are a hassle.

There's already a groove for in the pillow block for pulling the knives on a tersa head though...

[Darcy Warner]

Mine uses springs. I've debated about taking them out. They are a hassle.

There's already a groove for in the pillow block for pulling the knives on a tersa head though...

Spring loaded knives are great with the right setting gauge. I will look for the type of one that makes setting spring loaded knives a breeze. I could set all 4 knives in my Kolle planer in about 20 minutes and you were hard pressed to see any knife doing more work. Just as good or better than jointing the knives in the head of my planer.

[Tom M King]

To clear up some confusion: By "power planer", I meant hand held electric planers. None of my planers have a good way to use my method of setting jointer knives. Fortunately, Planer Pals work perfectly for the lunch box, and the big one has a built in grinder.

And yes, I meant 20 seconds, and not 20 minutes. Also, yes, I have checked with a micrometer. You can feel a thousandth of an inch. I use Boxwood because I have plenty of it. It's three times as dense as Hard Maple, but not necessary. I just like it the best for this. I have used anything from Yellow Pine to Corian. I don't like to put metal against a freshly sharpened knife.

You do have to keep presenting a fresh spot to the sharp edge of a knife, but it becomes second nature. Make sure to start with several pieces on hand, with both edges jointed perfectly straight.

I'd really like to try different types of jointers, but this method works great on any I've tried so far.

[glenn bradley]

Thanks, Darcy... adjusting the outfeed table turns out to be very easy. Now that I think about it, kinves have to be straight and all at the same height, which the jig ensures. If that height isn't exactly TDC, outfeed table can make up the difference.

You got it. Setting your knives to a consistent height using the outfeed as a reference will get you there or darn near there. In my world additional fine tuning is done via the outfeed height adjustment.

[Robert Engel]

Hey Marc,

I wouldn't think so as long as the distance from the. Anything under .003 is close enough for planer knives.

Before I went to a helical head, I used a dial indicator registered off the outfeed table. Sounds similar to what you're doing. I used two magnets placed on the outfeed table exactly the same distance from the blades & registered the dial indicator against them keep it parallel. TDC not as important as parallel to blades. Maybe you could do something similar.

You can also use a ruler and feeler gauge.

[Warren Lake]

I make sure my outfeed is parrallel to the head with a dial indicator. The dial will tell you top dead center of the head first. set the knives to a set amount above the head, you decide .050 above the head works for me. Dial indicator will get you to .0005 accuracy easy enough. I dont use the springs but had originally. one machine springs were replaced with an allen screw and threaded washer that sat under the knife but gave access so you could just turn the allen screw up and dial in what you want. The dial will let you check if your knives are straight as well, dont assume your knives always come back straight ive measured up to .015 off on a 14" knife. Enough times I have some screws a bit snug and am taping to make a straighter knife. In fact im usually a bit snug and up over my number and taping them down lightly to get what I want. I check the knife at each side and in the middle. then ill run it low get some snipe and bring it up. I have those magnetic things came with some knives a while back maybe one day ill try them.