How do you stop a jointer from tapering the board?

Hi Norm,

In this case, you may not be doing anything wrong at all: it could be the machine.

When it comes to jointing, it’s a 50/50 mix of proper technique and proper machine set up, so we’ll take a quick look at both.

Technique

First, let me preface this by saying that every jointer will taper boards to a certain degree. It’s the nature of the machine. When the taper becomes severe, you have a problem. To account for this effect, turn the board between passes so you start at a different end each time. Your last pass or two should be with the grain, however, to eliminate tear-out.

Pressure counts. When you begin, move the board toward the cutterhead with pressure on the infeed table. As soon as the end of the stock has passed the cutterhead, reposition your hand and put 95% per cent of the downward pressure onto the portion of the board on the outfeed side. Your infeed hand should be pushing the stock in towards the cutterhead rather than down onto the table.

Jointers make one edge straight, but won’t make opposite edges parallel. In my shop, I will joint one edge and one face, and then dress the opposite face with the planer. I dress the final edge on the tablesaw, equipped with a good ripping blade. You can follow up the cut on the tablesaw with a single, light pass on the jointer to clean up any saw marks if necessary.

Machine setup

In order for your jointer to function properly, there are two things that you need to ensure.

The infeed and outfeed tables must be perfectly coplanar. If either one is higher than the other, it will cause tapering. To check your machine, bring the infeed and outfeed tables to the same height and lay a long straightedge the full length of the tables. If you can see daylight anywhere under the straightedge your table(s) will need to be shimmed so that they are coplanar.

Once you have your tables properly adjusted, you need to set your outfeed table to just below the height of the cutterhead’s blades. Sit a piece of paper on your outfeed table and rest a straightedge (I use a piece of glass) on the paper so it sticks out over the cutterhead. With the machine unplugged, rotate the cutterhead by hand and see if the blades touch the glass. Your outfeed table height is perfect when the blades just touch the glass. You should be able to hear the blades tick off of the glass, but they shouldn’t move it.