Jointer Setup Tips

As I mentioned in my recent post on preparing wood for use, the jointer is one of the first tools used. To give your wood a flat, snipe-free surface with your power jointer, it pays to take a few minutes to make sure your jointer is set up correctly. Today, I'll discuss how to tune your jointer for optimum performance.

A jointer is a pretty simple machine that only does one job and does it very well -- make one side or edge of a board flat and straight. It consists of two tables, one slightly higher than the other, with spinning blades between them. To work correctly, the tables must be parallel to each other and the outfeed table must be even with the top of the blades. When edge jointing, the fence must be 90 degrees to the bed of the jointer.

Table Adjustment

We'll get started by checking the adjustment of the tables. Unplug your jointer and remove your blade guard. Also slide the fence out of the way or remove it completely. Place a long straight-edge across each table in various directions (e.g. end to end, side to side, and diagonally) to make sure that the table is flat. Look for any gaps between the straight-edge and the table. If one or both of the tables are not flat, you'll need to look at look at getting the table re-ground at a machine shop or getting a new jointer. If the tables are not flat, none of the remaining adjustments are going to help much.

Raise the infeed table so that it's even with the outfeed table. Using your long straight edge, check in several places that the two tables are parallel to each other. Ideally, you'd like to have a straight edge as long or longer than the total length of the infeed and outfeed tables, but use the longest one you can get your hands on. If there's a gap between your straight edge and the table, you will need to adjust one or both of your tables.

If you have a jointer with a parallelogram design, adjusting the tables parallel to each other is pretty easy since there are built-in controls for this. See your manual for details. However, most jointers use a dovetailed channel, called the ways, to support and adjust the tables. For this type of jointer, you'll need to shim the tables with some thin metal stock. Inexpensive feeler gauges make good shim stock and can be found at most automotive supply stores.

If you need to raise the end of the table, insert shims at the bottom of the dovetail ways. You may need to jack up the table a hair or have a helper lift the table while you insert the shims. If you need to lower the end of the table, insert shims at the top of the ways by unlocking the table, inserting the shims, and the locking the table down again. If the tables are twisted with respect to each other, insert a shim only on the side that needs to move up.

Kife Adjustment

The knives on the cutter head of the jointer all need to bet set at the same height. In addition, they need to be set so they are even with the outfeed table when they are at the top of their rotation. There are several ways to adjust your jointer knives:

  • Provided knife setting jig. If your jointer came with a jig to set the knives, you can use that. However, most jigs set the knives relative to the cutter head. Use a dial indicator to determine if the cutter head is even with the outfeed table before using this method to set your knives.
  • Dial indicator. Make a reference mark on the fence so that you line up each of the blades in the same place. Clamp a board to the outfeed table which is parallel to the knives. Set the base of your dial indicator against the board at one end and place the tip of the dial indicator on the tip of the knife. Zero out your dial indicator and then move the base to the other end of the board. If the dial indicator remains within a few thousandths of an inch from the zero mark, the blade is set correctly.
  • Aftermarket or homemade knife setting jig. There are several commercial jigs on the market intended to help you set the height of the jointer knives all the same and relative to the outfeed table height. The idea is that they hold the knife at the proper height while you tighten down the gib screws that hold the blade in place. The main downside of these jigs is that they require you to find the top dead center of the blade arc, which can be difficult to do accurately.

Once you have the jointer knives all set at the same height, adjust the outfeed table so that it is even with the top of the arc formed by the rotating knives. If you used one of the after market jigs, this should be pretty close, if not spot on. Otherwise, the technique I use requires a piece of wood about 6" long. Place the piece of wood so that it hangs off the outfeed table and over the cutter head. Rotate the cutter head by hand and note whether the knives hit the wood. If the knives move the piece of wood, raise the outfeed table until the wood barely moves. If the knives completely miss the wood, lower the outfeed table until the knives just touch the piece of wood.

Fence Adjustment

Now comes the easy part. Reinstall the fence, if you removed it earlier. Use a square to adjust the fence so that it is 90 degrees to the table. Reset the stop, if necessary. If you're like me, you won't have to mess with the fence after this, other than to verify that it's still square to the tables. I just don't use the fence at other angles all that much.

Finishing Up

We're almost done! All that's left to do is to test our adjustments and make some final tweaks. Find a piece of wood that is 2 to 3 inches wide, 1 to 2 feet long and already has a reasonably straight edge. Using the fence, make a pass or two on the edge of the board and check your results. If the edge is straight and square, you're done! Otherwise, you may need to make adjustments based on your results:

  • Snipe. Raise the outfeed table slightly, repeat until the snipe goes away
  • Convex Edge. The outfeed table is too high. Try lowering it until you start to get some snipe, then raise it back up a hair. If you're still getting a curved surface, the tables of the jointer are not parallel and form a very slight "V".
  • Concave Edge. The tables are not parallel and form a very slight inverted "V".
  • Edge not Square. The fence is either warped or isn't set 90 degrees to the tables.

Congratulations! Your jointer should now be ready for many hours of work. Apply a coat of paste wax to the tables and fence surface to make it easier to slide boards across the jointer. Most of these steps only need to be done once. There should only be a little bit of fiddling necessary when you have the knives resharpened.

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