Hello from Grenoble

[Doddy]

I have maybe a dozen toolholder, some give me no problem, some - mainly the ER32 collet holders that I bought from one Chinese vendor on eBay give me all sorts of gip.



View from under the spindle, looking up - you can just make out a round nipple just before the taper inside the spindle. That is, I understand, intended to engage with the keyway on the R8 collet.



This R8 collet holder is problematic... If I offer it into the spindle properly aligned there's no problem, but if, as I tighten the draw bar the tool holder rotates (not difficult) then the spindle binds and becomes stiff to rotate. I can only release the tool holder by rotating it until it aligns again with the nipple.

This second toolholder (all silver) ...



...doesn't have this problem (I cannot rotate this more than a couple of degrees when it's seated in the spindle, before I tighten the draw bar). You can see the keyway extends much closer to the taper on the tool holder.

I had tried manually re-cutting the keyway on a couple of spindles with some success.

EDIT:

From what I can see I think it's the depth of the keyway cut into the tool holder. Particularly with the arc at the end of the keyway as the depth reduces. At this point the tool holder can revolve and "jump" the nipple out of the keyway.