. .
  1. #1
    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

  2. #2
    LJ12A3-4-Z/BX or similar - cheap as chips from China.

  3. #3
    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 :)

    Click image for larger version. 

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    Fiction is far more plausible when wrapped around a thread of truth

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    Ralph Waldo Emerson


  4. #4
    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

  5. #5
    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.

  6. #6
    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.

  7. #7
    Appreciate that, but I use a mechanical switch NC as a limit switch, 5mm on from the home position.

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