After upgrading from my minimill to an Optimum BF30 mill and doing the cnc conversion, I have been debating what to do with the minimill. Sell it? keep it as a mill? Hmmm. I have also been looking around at designs for a 4th axis and it struck me that the head of the minimill might make a pretty good basis for a 4th axis for the BF30.

So the other night I set too and got the head off the minimill and from first inspection it looks like it will work quite well. The plan is to use a harmonic drive and stepper motor coupled to the minimill spindle for the motive power and attach an adaptor plate to the front of the spindle. In this way I retain the MT3 tapered bore plus I have mount point for lathe chucks and tooling plates if required.

Attached is the first bit of CAD, more to follow.....