bounce off home switch.

[Robin Hewitt]

Big chunky limit switches do not not necessarily give you good positioning, they are more concerned with reliability than a fine switching tolerance.

The best positioning switch is probably an opto slot with a built in Schmitt trigger. But if the switching point chances to align with a completed step you can still go +- one step.

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.
I'm going to give it a go, but that's only because I am totally anal

[Jonathan]

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.

[boldford]

As I've no need to machine metals I'm thinking of Hall Effect devices. I'm concerned mechanical switches or slotted opto devices might be affected by dust. No firm decision made yet.

[irving2008]

As I've no need to machine metals I'm thinking of Hall Effect devices. I'm concerned mechanical switches or slotted opto devices might be affected by dust. No firm decision made yet.

No need to use hall effect... simple magnetic reed switches work well although need debouncing just as a microswitch would. A hall effect device might just be too sensitive. With modern high-strength mini-magnets I found for one application I needed the hall effect device over 5cm away from the magnet before it stopped recognising it. Also the reed switches in burglar alarm sensors are ideal and not expensive £3.99 from maplin or £1.45 on ebay

[Jonathan]

I think the inductive switches I linked to in post 12 sound a lot easier than using reed switches, unless there's some advantage to using reed switches over them? SN04-N are the same ones DMM-tech use with their servo systems.

[boldford]

With so many ideas to choose from it will probably come down to cost v repeatability.

Hummm. . . . . So many design decisions. . . . . .