Thanks Gordon. So you made your own tools to do this. Please explain in a little more detail "the Ferrees one effectively still has pressure applied mainly across just a diameter".
A milling or CNC machine's collet chuck operates inside a tapered housing, in such a way that it applies pressure equally right around the collet.
The Ferrees tool is nothing like this. The clamping housing applies pressure on the collet across a diameter of the collet, i.e. in a plane at right angles to the split in the tool, because that is the plane housing the direction of force of the tightening device, i.e. the screw in the housing. Sure, the housing is shaped to fit the collet a bit, and that will stop the collet becoming excessively
oval, and ensure that the diametric force described, applies to a slightly greater sector of the collet at each end of the diameter, but the force is still applied across a diameter nevertheless, such that the collet is distorted slightly oval during use. When we are adjusting the minutiae of the shape of a tenon, this cannot be ideal.
A proper collet chuck system would be a lot better, but expensive. My system at least makes some
improvement by applying the force around the collet in three areas spaced at 120 degree intervals.
The photo shows my simple tool set up in a vice, but without the sax tenon in place. It was really a prototype, and would be quicker to use if it were made to fit the jaw of the vice, rather than being turned on a lathe, then cut to this shape.