Making the Perfect Tenon
by Phil Colson
Note: click any picture to see a larger version.
Understanding your chucks ability to hold a tenon or recess is of great importance. The chuck is at it's greatest holding capacity when the chuck is fully closed having all parts of the jaws touching the tenon or recess. As the jaws are expanded, less of the circle is making contact with the the fiber. This is one reason for different size jaws for the chuck. The face of the jaws needs to be flush against the fiber. If there is any space, the force of the cut presses the fiber against the face of the jaws and the other side starts to pull loose. The piece will start to vibrate and come off. Whether you use a tenon or recess to hold the piece, care should be taken to have straight or dovetail sides leading to a flat bottom.
If I cut a tenon the size of the closed jaws then the piece will fly off. I have settled on about 1/4" gap between the jaws. This allows tightening of the jaws and the crush of the fiber and still gives me a good hold. I made a simple jig. I opened my #2 and #3 jaws with a 1/4" spacing between the jaws. Took the measurement and transferred to a piece of phenolic. Cut it out on the bandsaw and sanded it smooth. Make sure the front edges are slightly rounded so they won't catch. It is now so easy to make the perfect tenon or recess, and yes I do like easy. Happy turning.
Phil can be reached directly via email at email@example.com.
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