Toolmaker needs to tap 30mm M6 into Aluminium, and is as cheap as me. Instead of one of us doing a hack job on a bench grinder (one of these days I'll make a jig), decided to setup my Hercus with a little grinder.

Started with the chuck:
IMG_0647.jpg IMG_0648.jpg

but the runout was terrible, so made use of one of Peter's collet holders:
IMG_0653.jpgIMG_0649.jpg


Failed to get a good action shot showing any sparks, but I was going VERY slowly – only 2 or 3 thou off each pass, and mostly hand feeding because my slowest auto feed was too much. End result pretty good:
IMG_0660.jpg


About 1mm off the wheel diameter, and about the same off the tap shaft!

There is a slight step, more runout further away from the collet.
Might be a bent tap, might be my imperfect collet taper machining.