1. #1
    ECCO's Avatar
    Lives in Tamworth, United Kingdom. Last Activity: 23-07-2016 Has been a member for 1-2 years. Has a total post count of 12.
    This is my first question on MYCNCUK. I am building a 3 axis CNC miller and have a question for all you learned CNC folk. It concerns limit switches on this machine. I would like to have double Hard limit switches on the Z axis to enable an easy adjustment on the lower Z limit. On both the X & Y switches have a single limit switch and software limits. Is this possible? I am using Mach3 CNC software.

  2. #2
    Yes it is possible. Have a look in your ports and pins menu in Mach. You will need to setup your soft limits and always remember to home your machine. I sould however recommend you have soft limits as a first safetynet and have the machine designed to have physical switches for the extents too. Just in case you forget to home the machine before preasing go.
    https://emvioeng.com
    Machine tools and 3D printing supplies. Expanding constantly.

  3. #3
    Quote Originally Posted by ECCO View Post
    This is my first question on MYCNCUK. I am building a 3 axis CNC miller and have a question for all you learned CNC folk. It concerns limit switches on this machine. I would like to have double Hard limit switches on the Z axis to enable an easy adjustment on the lower Z limit. On both the X & Y switches have a single limit switch and software limits. Is this possible? I am using Mach3 CNC software.
    Welcome to the forum.
    Why would you want a switch on the lower Z- as it would depend on what tool length you have etc.
    ..Clive
    The more you know, The better you know, How little you know

  4. #4
    Welcome to the party.!!

    Not quite sure what your asking here.? You say single switch on X & Y but do you mean one switch that travels with the axis. Or are you asking if it's ok to just have one fixed switch at one end and use softlimits for the other end.?

    Z axis often don't have a lower switch because usualy you'll have material on the bed with different thickness's and tools in the spindle with different lengths.
    If you crash then more likely the spindle nose will hit material, unless thin material, way before you hit the limit and that's allowing for the tool to be embedded into the material.
    Really the only time a lower limit is help full is for when your jogging up/down the spindle with no material on bed or tool in the spindle. All other cases then you'll either crash the tool into material or bed before getting near the limit.

  5. #5
    ECCO's Avatar
    Lives in Tamworth, United Kingdom. Last Activity: 23-07-2016 Has been a member for 1-2 years. Has a total post count of 12.
    First of all many thanks for your prompt replies. The idea is to have a lower Z axis limit switch that is easily and quickly adjustable, more for safety reasons than anything. This would mean having both upper and a lower limit switches fitted to the Z axis whilst having a single limit switch on both the Y and X and using soft limits set in MACH3. Do you think that this setup is possible?

  6. #6
    Quote Originally Posted by ECCO View Post
    First of all many thanks for your prompt replies. The idea is to have a lower Z axis limit switch that is easily and quickly adjustable, more for safety reasons than anything. This would mean having both upper and a lower limit switches fitted to the Z axis whilst having a single limit switch on both the Y and X and using soft limits set in MACH3. Do you think that this setup is possible?
    Possible but not practicable As Dean (Jazzcnc) has pointed there is no point in a -ve limit switch as you would have to adjust it every time you changed a tool etc.
    .
    Regarding the single limit switches and using soft limits in my opinion that would be a dangerous way to go as the soft limits would only work after you have homed the machine also if you stalled a motor the soft limits would not be correct in that the DRO would then be false.
    .
    If you only want to use one switch on X and Y then make it traveling with a target at each end.
    ..Clive
    The more you know, The better you know, How little you know

  7. #7
    Clive is spot on correct regards limits and soft limits it's a dangerorus combination really best avoided which isn't difficult to do.

    Regards the Z aixs lower limit then he's not quite correct but still he's right. You won't have to move the switch every time you change tool etc if just protecting the extents of travel but it's mostly pointless because your never likely to hit the switch because you'll have tool in the spindle and material on the bed 99% of the time.
    It's also got high potential for trouble from false trips etc because of all the vibrations and debris that get inflicted on Z axis down low.

    Better solution is to fit hard stops so the rails bottom and motors stall if for some reason you ever get anywhere near the travel extents. Which is unlikely if your cutting and have anything but really thin material on the bed.

    But to answer both your questions of is it do-able then yes it is. Would I advise it 100% NO.
    Last edited by JAZZCNC; 24-12-2015 at 11:42 PM.

  8. #8
    Building on Jazz's note, you can have one switch per axis as long as it is actuated both in both the + and the - direction. But you must have both directions protected! As I said above, the soft limits are only there as a means secondary safety and only work if your machine has homed (Like Clive says)

    here is a photo from practicalmachinist forum showing a single roller switch that is actuated by rolls that mount to the face of the table:

    https://emvioeng.com
    Machine tools and 3D printing supplies. Expanding constantly.

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