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  1. #1
    Join Date
    Sep 2003
    Posts
    1481

    Details on setting home and limit switches

    Mach 3, Win 10, smoothstepper, Gecko 540, BOB cs25, proximity sensors. Size 48" x, 36" Y, 7" Z. Two steppers driving the Y axis.

    I built this CNC aproximately 17 years ago and use it all the time but now I will soon be 85 and with memory not as good as it used to be, so I need to build some safety procedures into the CNC. I really would like to have a mentor that could give me accurate suggestions, rether than several users giving me their opions.

    I am using Proxcimity Sensors (PS) on X-, X+, Y-, Y+, Y slave, Z+ and moving metal near each one causes the Leds on each related input pin to light and go into a reset state, hitting reset twice removes that state.

    I have watched several YT's and I am unsure about positioning the gantry as to how close to the positive stop and the indication point.

    Let me describe how I think it should be set. Move the gantry aproximately 1/16" from the positive stop, then very slowly move the PS closer until the cnc senses it and secure the PS at that point. Is this the proper procedure, if not please tell me the proper method?

    Concern: I sometimes very slowly drive the Gantry into the left and right Y axis positive stops to make sure the gantry is in a square state, I set the positive stops with this in mind. Will I still be able to do this with the PS setting I described above.

    Thank you
    Hager

  2. #2
    Join Date
    Aug 2005
    Posts
    1120

    Details on setting home and limit switches

    Hi Hager,
    The +limits (the ones at the opposite end to the home switches) are only there to catch an issue where the software hasn’t stopped the axis. I.e, lost steps, etc.

    When you set up the home switch in Mach, you should also enter the max distance the axis can move from the home switch.
    When that is done the software will stop the axis from traveling too far. In this situation the +limit switch will never be triggered.

    Many machines don’t have a +limit switch and just rely on the software to manage the maximum axis travel.
    In the end it depends on the damage the machine will do if it doesn’t stop and crashes into the endstop. In a small machine, the stepper will stall and no damage done.
    On a large servo machine, it could destroy the servo and cause mechanical damage so a limit switch is required.

    Cheers

    Peter


    Sent from my iPhone using Tapatalk Pro
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  3. #3
    Join Date
    Sep 2003
    Posts
    1481

    Re: Details on setting home and limit switches

    Sorry but what you describe is not what I’m trying to find out how to do what i describe in paragraph 5. I know my post is a lot of words but I want to be sure you understand what I need.
    Please reread paragraph 4 and if you know how to do that please comment.

  4. #4
    Join Date
    Aug 2005
    Posts
    1120

    Details on setting home and limit switches

    You haven’t said what you’re trying to achieve. I was trying to cover a number of possibilities.

    Also, are the +ve PS or the -ve PS used as the home switches?

    If it’s how to set the position of the +ve limit PS, then the process is to jog the axis to the position you want as the maximum travel then mount the PS so it triggers.

    But, if you’re trying to use the PS(s) to remove “racking” where the axis is out of square, which seems to be what you’re doing when you drive the axis into the end stops.

    To do this with two PS(s), they need to be set up as home switches and not limits, at the -ve or +ve axis travel limit. Each switch is mounted on either side of the axis.

    The usual method for mounting is mount one of the switches so that it triggers about 1/8” or 1/16” before the axis would hit the hard stops.
    Then the other switch is mounted at the same 1/8”, but it is adjustable. This is the same process that you suggested.

    Then when the axis is homed, one side of the axis will stop when its home switches is triggered, with the other side continuing until its side triggers. If the axis is not square, then the adjustable PS is adjusted until the axis is square.

    When the machine is not homing, these switches are used as limit switches. If an axis triggers one of these switches the machine Estops.

    Cheers

    Peter


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  5. #5
    Join Date
    Sep 2003
    Posts
    1481

    Re: Details on setting home and limit switches

    Thanks Peter. Are you the same Peter in CNC NUTZ?
    I am using Proximity Sensors, not mechinical switches. Let's just talk about one sensor at the Y-- axis, generally refered to as Y HOME. (The fly in the ointment using Y is that there are two Y's, Y-- and Y slave -- called A in mach)
    If I move the gantry 1/8" from the positive stop, then slowly move the Proximity sensor tword the trigger plate on the gantry until the led on the Proximity sensor lights and the corresponding input number on the breakout board lights, that is the point I want to call Y-- Zero.
    What do I have to do in Mach3 to have it stop at that point if it is driven in theory past that point, say to minus 0.5"? If mach is set up properly in all it's screens it should stop at the point called Y zero. What screens do I need to accomplish this, and how to set thoes screens.
    Thanks Peter

  6. #6
    Join Date
    Aug 2005
    Posts
    1120

    Re: Details on setting home and limit switches

    No, Different Peter.

    I’m not in front of a computer at the moment. When I get home I can do a step by step.

    I presume that you have already setup the slaved axis and you need to set up homing, with the home position set at the Y max position.

    Cheers

    Peter


    Sent from my iPhone using Tapatalk Pro
    -------------------------------------------------
    Homann Designs - http://www.homanndesigns.com/store

  7. #7
    Join Date
    Aug 2005
    Posts
    1120

    Re: Details on setting home and limit switches

    Apologies, it completely slipped my mind, that I was going to provide the step by step instructions. The weekend got away from me.
    I’ll try to get it done tonight.

    Cheers

    Peter


    Sent from my iPhone using Tapatalk Pro
    -------------------------------------------------
    Homann Designs - http://www.homanndesigns.com/store

  8. #8
    Join Date
    Sep 2003
    Posts
    1481

    Re: Details on setting home and limit switches

    Thats fine Peter no rush, so much isnt working on the cnczone. I wasnt seeing my posts and replies but a member showed me a work around of the cnc system searches I was only seeing posts prior to 2018, but he work around pretty michey mouse but works. Thanks Peter

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