Re: 5C collet boring
Pretty hard to stuff a 1.250 plug in a 1.250 hole. Maybe 1.251 hole would be better. I would bore the hole at about 1.255 except for the last 1/2 inch or so forward of the threads, that would be bored to 1.251, this allows easy insertion of the collet. Then, past the back of the collet, the bore needs to be larger to clear the OD of the draw tube, unless you want to use the ID threads in the collet for a draw bar. The ID threads in the collet is normally used for a collet stop.
The nose taper should be ground, I have done this with a tool post grinder. But it could be turned and still work.
Jim Dawson
Sandy, Oregon, USA