If you are lucky you might get the speed control from the tread mill.

Ian S C

Again, from my Sharp mill, this is the vertical spindle dis-assembled:

Very simple but robust. The thread on the nose is Myford 1 1/8" x 12. Not relevant to you I should imagine. The bulk of the shaft is 1" OD, slightly relieved in the middle. The bearings are 1" id and are a sliding fit on the spindle, the 2" OD bearing shells are a press fit in the cast iron head. The shaft is retained by the collar which can just be seen on the left, this has a fine-ish thread and is split but can be tightened with a socket screw to close up the split. The thread on the shaft is hidden in the picture by the right hand bearing. The spindle is bored through and has a No.2 Morse taper. The spindle is not hardened, consequently, taper tooling can become very tight and require significant bashing to release (hence the dis-assembly and bearing change). I would advise incorporating some sort of alternative release mechanism if going down the Morse taper route.

HTH,

Rod