I “test fitted” the sensor circuits to the gantry tonight and I’m pleased to say that they work with a surprising degree of accuracy.
The sensors are wired to input pins 11 (X), 12 (Y) and 15 (Z). I used the Mach 3 “auto set” feature to configure the pins as home for M1, M2 and M3.
A neat feature of the homing functions (Ref) in Mach 3 is that it homes past the switch limit, then backs up to the on position, so the home is always referenced from the same position.
UPDATE : After giving this some thought it occurred to me that the home position doesn’t really have to be at the origin at all. It just needs to be a fixed reference point, so that the machine can “pick up where it left off” from a known location. Changing the tool on the router will typically nudge the motors and cause the software to get out of sync with current position.
I believe it is possible to script Mach3 to move to a fixed offset away from the “home” position, and use this to set the start point for the cut.
I’ll have to put together a movie that shows how Mach3 is configured too.