Advice on toolholders

[lucan07]

If you wanted to go ahead with this I would look at getting some sort of keyway set up in holder, should be possible.

[Rabs]

Sorry, I'm not sure I understand. Do you mean I should add a keyway if I bore out the spindle, or if I use a screw in toolholder?
There is a keyway on the spindle taper at the moment. A ball bearing on the outside of the coventry chuck engages with it but it doesn't appear to be designed to take the cutting loads but rather to help you align the chuck the same way each time (I guess that the final grinding on the internal taper on the chuck may have been machined in-situ so you'd want to replace it in the same orientation each time to minimise runout)

[lucan07]

If you use screw in toolholder, not so much for the cutting loads just to prevent locking in any tools.

[Rabs]

Ok, thanks. I'm still not quite with you though - sorry! If the toolholder screws in then it has to rotate, so how can I have a keyway? I suppose I could screw in the toolholder get it to register on the taper and then push a loose key in afterwards? But to give good alignment on the taper doesn't it have to be tight to the taper? In which case, anything that stopped the screw from tightening would also stop the taper from doing it's job properly to keep the tool aligned. Have I misunderstood?