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Aligning a Jointer

The Tools

The only truly effective way to align a jointer is to use a dial indicator. You need a stable platform to mount the dial indicator on so that the indicator can be held over the knives or the opposite table. Here's a diagram of what my jig looks like:

I built a jig that consists of a 3"x8" block of 4/4 hardwood, a riser block attached to one end and an arm attached to the riser block. The DI is secured in a hole in the arm such that the tip of the DI stylus extends 1/8" below the bottom of the hardwood plate at a point 2" from the end. (Just imagine the wood block sitting on a jointer's outfeed table with the tip of the DI resting on the knife edge) I installed a 3/16" flat-end stylus in the indicator.

Here is a picture of the finished jig.

You also need an accurate combination square, but a small double square can also be helpful.

The Process

Okay, so you've bought, built or borrowed an alignment tool like the one I described above. Here's the alignment process:

1. Rotate the fence out of the way, as I did, or remove it altogether. Set the jig on the outfeed table and zero the indicator. All measurements will be made with the jig resting on the outfeed table.
2. Raise the infeed table to the top of its travel and reset the depth of cut indicator so that it reads '0'.
3. Straddle the jig over the cutterhead with the stylus resting on the infeed table. Lower the outfeed table below the infeed table, then raise the outfeed table until the indicator reads '0'. Lock it down.
4. Rest the indicator stylus on a knife edge and rotate the cutterhead until you find top-dead-center. (The position where the indicator reading is at its maximum) Make a mark in the center of a 6" piece of masking tape and stick it to the back of the jointer bed, spanning the cutterhead gap, with the mark aligned precisely with the knife edge. (You don't want the tape to interfere with the cutterhead rotation)
5. Now the fun begins. Loosen the nuts securing one knife, lower the jack screws by about one turn, and press the knife (carefully) down with your fingers. Next, snug up the two outermost nuts, but don't actually tighten them. You still want to be able to raise the knives with the jack screws.
6. Rotate the cutterhead to align the knife edge with your TDC mark, then rest the indicator stylus on one end of the knife. Raise that end until the indicator reads about .002" less than 0. Repeat with the other end. Then raise the first end to .001" less than 0. Repeat with the other end. On my jointer, that's where I stop. Tightening the nuts securing the knife takes up that last .001". I go on to the next knife when the indicator reads precisely 0 at both ends of the knife and all the nuts are tight.
7. Repeat steps 5 & 6 with the remaining knives.
8. Return the fence to it's normal position and adjust it so that it's square to the infeed table.

Adjusting the Tables

If you've adjusted the knives perfectly and you still cannot get a good cut on your jointer, the jointer's tables might be out of alignment. Here's a brief description of how they can be aligned:

The key to aligning the tables is to find an accurate straightedge about as long as your jointer bed and a cheap set of feeler gauges. ("Cheap" is the operative word) You might actually need two sets, depending on how lucky you are.

Start by adjusting the gib screws on the outfeed table to make sure the outfeed table is snug in the sliding ways but can still be adjusted easily. Raise the infeed table to match the outfeed table and lay the straightedge across both tables. Use the feeler gauges and a bright light positioned behind the jointer to observe how the tables are aligned. You probably want to check the alignment across the front, the back and both diagonals to get a feel for how the outfeed table needs adjusted to get the tables coplanar. Then, loosen the gib screws so that you can lift the outfeed table slightly away from the jointer body and insert the feeler gauges between the outfeed table and the jointer body. Insert the feelers under the outboard end of the outfeed table to raise the end of the table, or nearest the cutterhead to raise the inboard end of the table. You'll just have to experiment with different thicknesses of shims until you find the right combination and positioning of the shims. You might end up needing the same thickness of shim material on both sides; that's why having two sets is sometimes nice. When you find the perfect shim thickness and location, cut an inch or two off of the feeler gauge and leave it permanently in place. (That's why you want cheap feeler gauges. You'll end up sacrificing a couple of the gauges) Once you get the outfeed table coplanar to the infeed table, tighten it down and leave it alone. It's usually best to re-adjust the knives to align them with the outfeed table instead of moving the outfeed table.

Obviously, since you've moved the outfeed table all over the place so you'll need to re-adjust the knives when you're finished.