I’ve been working on a revised set of shapeoko-2 endstop parts, and now they’re up at Youmagine, along with a few pictures. I decided on mechanical endstops for all three axes, both because that’s electrically simpler and because microswitches are way more repeatable than you would think. The ones in my 3D printers appear to be good to at least a tenth of a millimeter, which would be a couple widths of a human hair, and almost certainly way less than the flex in the rest of those machines.
I was thinking about something different for the Z axis but finally decided that would be stupid. The gold standard is an electrical-contact sensor between the bit and a perfectly measured plate set into (or onto) the bed of the machine, but that means something that will maintain electrical continuity with the bit and chuck while not in any way interfering with their rotation at 30,000 RPM.And I’m too lazy to debug that. An optical sensor would be fine, but I can’t figure out something that will be equally sensitive at registering a 3mm end mill and a 0.05mm engraving point.
So I settled for a separate, adjustable probe and a microswitch. If that ever turns out to be the limiting factor for the machine’s accuracy (stop laughing whenever you want) I’ll fix it. Except the S2 has a new spindle mount. I can’t use the trick from the S1 of letting the probe lock into the aluminum extrusion that holds the spindle, because there isn’t one. So I printed up a cute little piece that bolts to the spindle mount and holds a piece of leftover aluminum 1/8 x 1/2″ bar stock. The M3 bolt that locks the bar in place is also left over, from my original Cupcake CNC build. Thanks, Reprap Research Foundation….