Fixing Manual Mill Spindle - No Contact Between The Taper of Tool and Spindle

[tonyfoale]

I did something similar to covert an R8 mill spindle to an ISO 30 taper. I rotated the head to half the included angle and bored the spindle using the vertical table/knee feed. It would not work using the quill feed, that would just bore a parallel hole regardless of the angle.
It is important that the tool edge is set on the centreline, the equivalent of setting tool height on a lathe.

This method ensures good concentricity, better than removing the spindle and cutting the taper in a lathe where there will always be some runout.

The same technique can also be used to repair a damaged R8 taper.