Go to limit switches for a small-ish mill?

[alanambrose]

Any recommendations for accurate limit/homing switches for a smallish mill? I'm thinking probably hall-effect rather than mechanical but that's only an uneducated bias :)

TIA, Alan

[cropwell]

LJ12A3-4-Z/BX or similar - cheap as chips from China.

[Fivetide]

What you using as a controller Alan ?
Some of the new chips use soft-limits - works on voltage drop.
Or you could hard stop it save wiring like mine :)

[alanambrose]

This is an old Gecko G540. Call me old-fashioned but would prefer an 'actual' switch. I'm getting the sense that LJ12A3-4-Z/BX and the like are ~5-20μm repeatability?

Alan

[cropwell]

Probably much better than an 'actual' switch as there are no mechanical parts to wear out. LJ12A3-4-Z/BX is used extensively in industrial process automation. It would be interesting to see some actual figures on the accuracy of sensing for both inductive and mechanical switches, especially in a swarfy environment. I am discounting Hall switches at the moment. For some reason I do not regard them as the best solution for positional sensing on a machine tool. (Although I would like to hear arguments for and against the case).

I did some testing on my gantry homing, putting a line on the stepper shaft and it came back to exactly* the same position every time, no matter how far away it homed from**.

Exactly* is an observation of angle of the line, not a measurement with a dti or similar.
** Mach3 homing would compensate for this, by doing an approach and back-off.

[dazp1976]

LJ12A3-4-Z/AX
NPN-NC (normally closed) type or similar is preferred for me.
If you get a signal wire break it will see it.

A normally open type will not see a broken signal wire and let you carry on.

[cropwell]

Appreciate that, but I use a mechanical switch NC as a limit switch, 5mm on from the home position.