Quote Originally Posted by Robin Hewitt View Post
Perfection is probably a side paddle arm on the screw that winds into an opto slot. That would allow you to adjust the switching point to mid step.
Perfect perfection would be to put the opto slot on the stepper motor or ballscrew - the rear shaft on the motor would be pretty convinient. If you put the sensor/slot at say 30mm radius then one step is amplified to just under 1mm movement instead of 0.025mm (or whatever). Trivial to detect 1mm, but you would need two sensors. One standard switch on the axis as normal to get it close, then look for the signal from the 'rotary' sensor to get it spot on.
That's what I'm doing on the next machine anyway - inductive to get it close, then optical on 30mm radius disc for perfection.