South Bend 9A Lathe 3C Collet Drawtube

In my humble opinion, for truly accurate collet work, EVERY element (collet, adapter, spindle taper, spindle bearings, draw tube threads, draw tube centering sleeve, hand wheel thrust face) of the system MUST run truly on the same axis. Or, off-axis errors must have compensating (equal but opposite) errors.
In this video I show how I made a 3C collet drawtube for a 9A South Bend workshop lathe. I tried to make ALL of the functional elements on the same axis by chucking the part ONCE. The indicator shows a 0.000050" (50 millionths of an inch!!) TIR one inch from the collet nose. Not bad for a 70 year-old lathe.
DISCLAMER: Of course, your results will also depend upon the fit and adjustment of the spindle bearings, the precision of your spindle taper, the precision of your MT3-3C adapter, the precision of your collet, the precision of the material held in the collet, how true the alignment sleeve runs, how true the hand wheel thrust face runs and the phase of the moon.
Additionally, the rigidity of the test indicator stand and the required plunger pressure will affect the accuracy of the test results. Did I mention the affects of temperature?

[@miguelcastaneda7236]

Thought the 3c was a 5/8 26 pitch..bigger major. Iike .008 thou...on the collets

[@FCleff]

Hi, thank you for your comment. The threads on a 3C are 0.642-26. The body neck diameter is 0.649". I don't know the tolerance for the neck diameter but I imagine it's +-0.0005 .
Cheers,
F.C.