My tenon cutters are designed for the final fitting of the joint. The less wood taken off the tenon, the smoother the cut will be. It will also be less likely that the tenon will get cocked on the part.
I hold both the tenon cutter and the part in my hands, since I feel that putting the tenon cutter or part in a vise increases the likelihood the tenon will be askew. While using the tenon cutter, put pressure straight into the tenon cutter and pull very slightly up on the part. Pushing down can cause the tenon cutter to pencil-point the tenon. For tapered tenons, stop cutting when the end of the tenon is flush with the left side of the tenon cutter. For cylindrical tenons (i.e. spindle tenon cutters), you will get a 1″ long tenon if you stop with the tenon flush with the left side of the tenon cutter. For longer or shorter tenons, the point where you want the tenon to end (and the tenon’s shoulder to begin) should be centered in the tenon cutter when you stop cutting.
You may now have a shoulder on your tenon. For tapered joints this must be removed, for if it bears on the edge of the mortise it will keep the tenon from seating, causing a bad glue joint. Regardless, it tends to look bad. The part can be chucked in the lathe if the lathe’s center-mark remains, or using a drawknife or chisel will work fine. A spokeshave is more dangerous — it is difficult to tell when you are cutting the tenon itself.
ADJUSTING TENON CUTTERS
You will need to adjust the blade after sharpening if the blade has been knocked, the tenon cutter’s body has moved from moisture changes, or in order to change the diameter of cylindrical tenons.
Set the blade too far back so it won’t cut, with the left edge of the blade flush with the body of the tenon cutter. Tighten the screw lightly. To adjust, put a screwdriver against the blade and tap the screwdriver with a hammer. If you go too far, pull the blade back and try again. Putting a finished tenon into the tenon cutter can help show roughly how far to drive the blade forward. The finer it cuts the less it will tear, but the slower it will cut.
For tapered tenon cutters, the way the blade is cocked in the body has some effect on the taper the tenon cutter will create. Check that the tenon cutter is creating the correct taper. You can use your reamer’s blade as a reference. Tapping the corner of the blade with the hammer and screwdriver will rotate the blade without advancing it.
For cylindrical (spindle) tenon cutters, if the blade is cocked to the left it can create a tapered or undersized tenon.
Tighten the blade all the way and you’re back in business!
Tenon cutters can be purchased here.