Setting Jointer Blade Height

      Experienced hands go over the fine points of setting up a jointer for snipe-free operation. June 23, 2005

I am wondering if anybody has any recommendations on setting the height of the knives on a jointer? I have recently tried to set up a Sears 6 1/8 jointer as a secondary machine operation that I had picked up, and the manual states that the knives should be set to .002-.003" above the out-feed table. My main jointer has a jig for setting knives.

I have done a little research on this, and have found that there is a lot of conflicting information.
My information from the people at my local tool supplier said that all jointers should be set even to the out-feed table. I have been able to set the tables properly with the aid of a machined strait edge. Am I just wasting my time, or is there something that I'm overlooking? Any help is appreciated.

Forum Responses
(Solid Wood Machining Forum)
From contributor R:
Is it a model that has a fixed back table? I had one of those a while ago, and it was pretty tricky to setup.

From contributor L:
In theory, they should be set to be even with the out-feed table and setting them a few thousandths higher doesn't make that much difference. Setting them a few thousandths lower will result in a taper, so it's often recommended to set them a few thousandths higher, which will account for wear as the knives dull.

I set up machines for a living and as simple as a jointer may seem, it takes a lot of practice to get the hang of it. I can set the four knives of our 20" jointer in 20 minutes, but I use a special dial indicator and I can get the knives within .0005" of each other. I've done some tests on how much our planer knives are reduced in height as they dull, and found .005" to be a common amount in our shop.

We do antique lumber, so the knives get more abuse than planing new lumber. Your machine is fine, but it will take some practice to learn how to set the knives.

From the original questioner:
To contributor R: If you are referring to the in-feed or out feed, it's the in-feed that is adjustable.

Contributor L - I had a good idea that the theory of .003" would not make that much of a difference, but it does. I have tried setting the knives at that, and with the bed set a zero ( flat to each other), I still remove stock with about 5/8 length of snipe.

From contributor J:
To the original questioner: I agree with Contributor L if you’re just roughing out boards to get ripped into strips for a molder. But if you’re doing full length glue joints or precise cabinets, make to have the knives even with the out-feed bed. If you can tell that the knives are wearing over time, slide your fence over to a fresh spot.

From contributor L:
To contributor R: I don't use the adjuster screws, even if they are present on the head. I always work the knives in position by moving them down, not up. I learned how to do that on the heads that don't have adjusters, so it's no big deal.

Getting the knives level with the table is ideal, but a lot of people have trouble doing it that close, so they are fine having them a few thousandths high. Anymore is a significant amount of snipe.

From contributor R:
To contributor P: There is no out-feed table adjustment! After you put all the knives in, you have to run a board to see if it cuts straight. You might have to set the knives 3-4 times or more to get anything straight on lengths over 4'. With no adjustment on blade height, it’s a tedious job. What usually happens is either you get a new jointer, or you use the tablesaw with a straight-line ripping guide.

From the original questioner:
Thanks for all of the responses. Over the past couple of days I have reset the knives to .000. The knives have a jack screw adjustment, and with my machined strait edge I was sure that the knives where dead even with the out-feed table. Then after checking that both tables were parallel with each other, I made a test cut. As I ran the board, the snipe was (to my surprise) about 1/2". The second pass was less and the third looked good.

I would like to know why I would have any cut, not to mention snipe, on a jointer that has the knives set even and the in-feed table at .000. The straight edge that I am using is a special machined 36" piece of square stock I received from a machinist so I know it’s dead flat and straight. I must be doing something wrong.

From contributor L:
What you describe clearly shows that your knives are higher than your out-feed table. Snipe isn't measured in length. If you measure the width of your board with a caliper, you will find the snipe section is perhaps .005" (guesstimate) different than the main part of your board. That tells you how much higher your knives are. This would be one reason to justify being able to tweak the out-feed table a bit to compensate. Since you can't, it means re-adjusting your knives.

It's easy to describe the principle of using a straight edge to set the knives this way, but it takes a lot of practice to actually be able to realize such subtle differences of several thousandths. Typically a much smaller straight edge is used in the setting of knives.

You might want to try a small piece of hardwood and see if that works better. That machine is possible to set better, but it takes a lot of practice. I use an indicator and a special base so I exactly know where I am in relation to the out-feed table. The straight edge method isn't as precise. An indicator can be bought from Enco for around $16, and the base can be made from a block of wood. The indicator bases available from suppliers won't work anywhere near as well as the block of wood. I would also recommend a wider tip. I use a 1/2" convex button tip on my jointer setting jig.

From contributor L:
Here's something to try. Set your knives about 1/32" high to the out-feed table and have the first and last gib screws just barely tight enough to keep the knives from falling out. Then take something flat, like a piece of ply or even a piece of 1/4" glass, and hang it off the out-feed table. Then rotate the head by hand slowly, and the knives get pushed down and will be even with the out-feed table by the overhanging piece. It takes a bit of practice to get the gib screws at the right tension, but it's relatively fast to do this procedure. It works well for 6" jointers.

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