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  1. #1
    Join Date
    Dec 2006
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    947

    Home Limits Problems

    I have a CNC router that I built from scratch and I'm using the Home buttons for Home and X--, Y-- Z++. When I hit REF All Axis sometimes it returns to home fine but other times it does not jog off the limit/home switch enough and it makes the system stop. I'm using leaf type switches for limit switches. Is there a way to change the distance it will automatically jog off of the limit/home switches when sending eveything to home? Thanks.

  2. #2
    Join Date
    May 2006
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    1469
    What you can do is increase the debounce interval.

    That will in effect make the axis move further off the limit when homing.

    Greg

  3. #3
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    Dec 2006
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    Thanks for the responce, although I have no idea what that is LOL. I will look it up on the help file.

    Just as a another question do most people use leaf type switches or proximity sensors? I don't think the switches I'm using are that accurate and if I'm trying to return home and that be the exact point every time I'm not sure it'll work. I figure a proximity switch would be more accurate?

  4. #4
    Join Date
    May 2006
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    1469
    Debounce Interval is on the "General Config" page in the top right corner.

  5. #5
    Join Date
    Jul 2005
    Posts
    2415
    "Leaf" swtiches are more accurate than you realize. I have always used the lever arm type small microswtiches and find them to have good repeatablity (which is what you want) I set up a dial caliper that showed me the deviation each time it homed and It easily held .0015. On an router table or plasma table that is plenty close. Of you were on a big accurate mill and wanted more accuracy than that you could look at optical (vane) type switches.

    So I guess you have to define "exact point". If that means +-.0005 or less then you need to think optical with servos and encoders with an index feedback tied to the home switch. Personally my stepper router has precision linear slides and med resolution (1000 [true] steps per inch before microstepping) I have no trouble drilling precision plates (aluminum). For wood cutting ....it's less critical.

    tomCAUDLE
    www.CandCNC.com
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  6. #6
    Join Date
    Dec 2006
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    947
    I'm having a brain lapse right now. I don't have leaf switches but the ones you mention the lever arm switches. Anyway, I'll try the debouce. Thanks for the suggestions.

  7. #7
    Join Date
    Dec 2006
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    947
    Another quick question. I can't seem to get the Manual override function to turn on. I can get the Auto LimitOverRide to turn on but not sure what it does. I've watched Art's turtorials and it seems that Manual override should be able to turn on and allow me to jog off of the limits.

    When I hit a limit 90% of the time I CAN'T jog off, I have to physically go short the switch to allow me to jog off. Any suggestions?

  8. #8
    Join Date
    Dec 2006
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    947
    Greolt, I found what you're talking about but it's a time based function and I have no idea of how to set it or understand what it's doing. Why would it use time instead of like, jog off of limit switch .125"?

  9. #9
    Join Date
    Dec 2005
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    1408
    Geof's post #8 on this thread

    http://www.cnczone.com/forums/showthread.php?t=43105

    has a really nifty idea of how to get better accuracy by using two switches for homing.

    Best wishes,

    Martin

  10. #10
    Join Date
    May 2006
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    1469
    Quote Originally Posted by Cartierusm View Post
    Greolt, I found what you're talking about but it's a time based function and I have no idea of how to set it or understand what it's doing. Why would it use time instead of like, jog off of limit switch .125"?
    As I said Mach does not have a setting to adjust that distance to .125"

    The debounce is a setting designed to overcome the problems of switch bounce. Do a search to understand what that is.

    By setting the debounce to say 2000, when homing the axis will move a little further off the switch before Mach actually sees that it has.

    It is a work around, and one that Art (the author of Mach) often sugests to users with your question.

    Greg

  11. #11
    Join Date
    Dec 2006
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    947
    Thanks I'll try that. How come I can't check mark the box for manual override? Like I said most times I can't jog off after hitting a limit switch.

    Usually what happens is I'll hit "Ref All" and it will start to home after Z gets to where it's supposed to go and then as Y is moving the Z will trigger again and I'll have to unplug the switch and short the wires to be able to jog off just a hair.

  12. #12
    Join Date
    May 2006
    Posts
    1469
    What sort of switches are you using? Do they have a nice positive action?

    This sounds more like a mechanical problem. Are they mounted securely?

    After the Z has homed and the Y is traveling toward home, maybe there is enough vibration or "wobble" to retrigger the Z switch.

    It could also be electrical "noise" retriggering it.

    Maybe a pic or two might help.

    Regarding the failure of the "manual override" I am guessing that because you are getting a limit switch doing a
    reset during the "Ref All" macro that the macro hangs. That is just my guess.

    I would expect that once you get your switch acting more reliably that that problem will go away.

    Greg

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