Because we're talking about a "broaching" sort of tool, there's not likely to be much force trying to rotate the spindle, so you shouldn't need a fierce amount of locking...
1) Bridgeports have a lever that applies a brake to the spindle pulley. Theirs is spring loaded to the OFF position, of course, since it's just for wrenching on the drawbar, but you might do something like that (minus the auto-off feature), especially if you have converted to belt drive.
2) If you have belt drive, you might rig a non-rotating "pulley" to which you could move the "motor-end" of the belt, then apply tension.
3) Make a custom spindle-lock pin with an oval cross section. Insert in the factory locking hole, then twist to take up the clearance. (You'd have to do your fine tuning of cutter direction by rotating the cutter in the toolholder or collet.)
4) Fabricate a bracket to hold a thumb-screw that can tighten down against the top of the spindle pulley...
4b) ...or horizontally against the belt in the pulley groove.
Paul in Pittsfield
--- In GrizHFMinimill@yahoogroups.com, "kr98664" <kr98664@...> wrote:
>
> Hello All,
>
> Any suggestions of how best to add a spindle lock to my Micro-Mark R8 mill? Today I made a new cutter from a piece of drill bit and then used the Z axis to make my first internal keyway. (I was replacing a broken handle on my lathe.). I was quite pleased with how the keyway turned out, but I had to jury-rig a means to lock the spindle. I'd like to add a lock that would let me fine tune the direction the cutter is pointing, if that makes any sense.
>
> Thanks,
>
> Karl
>
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