Cheers, so I probably need a lock nut as well then? The original one just squeezed the inner race on to the step on the shaft.

The other problem is how to drill the hole in to the end of the quill for the chuck lock bolt. I foolishly thought it would fit in the lathe but that also has an M2 taper, Duh

Is it safe/accurate to hold a drill bit (facing up) in a vise and lower the quill down over it?