Shugart 800-8 media centering problem

[tony duell]

> Certainly one of my thoughts along the way.  But, the spindle cone does
> not rock or anything like that.  And, I switched the clamping part out
> with another drive - neither was affected by the swap.

It strikes me that there are 3 main subassemblies associated with clamping the disk : 
The cone; the clamping arm; and the spindle. If you have proved the first 2 are OK by
using them in another drive (admittedly not a perfect test, but it suggests they are not
the problem) then I would look very carefully at the spindle.

Making a replacement cone is possible, but not easy, given the accuracy needed. It
appears that the spindle in my drive is in 2 parts, the cone is pressed onto the end of
a metal spindle. I think if I had to make it, I would make the spindle rod first, rough out 
the blank for the cone, leaving it well over size  then press the  blank for the cone onto
the end, hold the spindle in a collet (a 3 jaw chuck is nowhere near accurate enough) 
and then turn the cone itself. 

-tony