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Cutting perfectly matched tapers on opposing sides of a leg is easy. The secret is in the shim as explained below.
Click image to enlarge

Cutting Opposing Tapers

Better than "almost" right

Text & Photos by Tom Hintz

Tapering adjoining sides of project parts like a table leg is easy with a commercial or shop-made tapering jig. Make one cut, roll the leg 90-degrees and cut the second side. As long as you marked the faces to be tapered and then actually cut those sides, all is well. When the tapers are on opposite faces 180-degrees apart, the process gets more complicated.

Note: If you are new to using or need a tapering jig, see the Resources list at the end of this story for additional information on making a jig and using it.

The "Almost" Method

When I learned how to make opposing tapers, the procedure seemed pretty straight forward. Lay out the tapers on the blank, adjust the taper jig for the first side and make that cut.

Set up the taper jig and make the first cut normally. Save the scrap!
Click image to enlarge

For the second cut, there were two commonly accepted methods. One was to re-adjust the taper jig for the second cut. That was not only inaccurate but the tapered side against the jig could rock. Not a good thing to push through a saw blade.

The second method involved taping the waste from the first cut back in place and make the second cut without adjusting the jig at all. That eliminated the rocking to a large degree but to get that side of the leg flat, the scrap wedge had to be slid up to compensate for the saws kerf. That left the bottom uneven enough it may not catch the heel of the jig.

The biggest problem is that neither of these methods fully account for the wood removed by the blade itself. Taping the waste back on gets you close but that side of the blank still is not flat over its full length. In addition to the obvious inaccuracy, if the piece rocks or slips on the jigs’ heel during the cut, a kickback can occur. If you are lucky, only the workpiece will be damaged.

Make a Shim

Securely tape the waste back on with the shim (arrow) sandwiched between it and the leg. Make sure the bottom edge is flat to catch on the jigs heel.
Click image to enlarge

To make cutting the second face safe and accurate, we have to replace the wood lost to the blade during the first cut. Adding a shim equal in thickness to the blade kerf, (usually 1/8") between the workpiece and waste restores the original dimensions and makes that side straight again.

I made a long piece of shim that has been cut into a few lengths to fit previous jobs with all of those kept where I can find them. To make the shim I trimmed an oversize leg blank just enough so that the blade cleaned up that side. Then, the fence was adjusted ¼" closer to the blade and a second cut made. The waste from the second cut is exactly 1/8"-thick.

Note: If a thin kerf blade is used, measure it's width and add 1/8" to determine how much the fence has to be moved towards the blade to produce an 1/8"-thick shim.

The Second Cut

Put the first cut against the jig and cut the second taper without any adjustments. If the shim matches the width of the blade, the second cut is perfectly in line with the first and the sides of the leg are equal.
Click image to enlarge

Cut a length of the shim long enough to fit between the original waste and the blank. The shim should run from the bottom of the leg to near the upper end of the cut without sticking out. Using masking tape, secure the waste to the blank with the shim between them. Keep the bottom edge flat so it can rest on the taper jig stop correctly.

I use three or four pieces of masking tape to secure the waste and shim to be sure it is secure. Adding one more piece of tape to the blank in the uncut portion above the taper evens out that side of the blank so it can rest flat against the taper jig without rocking during the cut.

Put the taped side against the taper jig (no adjustments) and make the second cut. If the taper jig is still at the original angle, the second cut will match the first almost perfectly. Of all the tapers I have made using this procedure, none of the second cuts appeared any different from the first.

Remove the tape, waste and shim before sanding or jointing the surface smooth. If a jointer is used, take the same number of cuts from each taper.

Remember to save the shim pieces for future use.

Resources

Taper Jig Plan

Using a Taper Jig

Tool Room Jigs Page

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