A couple of days ago I started installing the limit switches. I went with electromechanical micro switches with roller actuators for the X and Y, two per axis, and optical interrupter detectors on the Z axis, again 2 per axis.
I got the two X axis switches installed no problems - drilled and tapped 4 M3 x 0.5 holes.
Alas, tragedy struck on the lower Z axis plate - the tap broke off.
The tip is embedded about 10mm deep, with a small <1mm shard sticking out above the surface. I tried spinning it with a vibrating engraver tool, but as the pic shows, all that did was bugger up the aluminum. So instead of fussing with removing the broken tip, I just used one screw and some 3M VHB double sided adhesive foam. No mechanical force, so it should be fine.
Problem is, I can't continue because I don't have another 3mm tap. It was part of a cheap tap/die set. Lesson learned: spend the money for high quality individual taps. I ordered some good ones online, should arrive this coming Wednesday July 5.
Meanwhile, I'm going to work on patching the Mega2560 into the stepper board and hopefully get the motors moving under GRBL.