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Thread: CNC 'jumps'

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  1. #1
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    CNC 'jumps'

    So I have hardly used my CNC in the last few years but am running Mach 3 on a Windows XP desktop. It had been working fine until one day my Bosch router quit working and it dragged across the work surface until I hit the stop button. I bought a new Bosch router but ever since then I have 2 places where my X axis 'jerks' and messes up my material. I'm not sure if something got messed up in the hardware or in the Mach 3 settings? It may not be related to the router hang-up at all. I rarely ever use it so it might have been months later that I noticed it. But wife wants me to make her a sign but I can't use it until I figure this out. Any ideas what might have happened or how to fix it? Should I just re-install the file for the controller? I bought this brand new off eBay several years ago and received the file needed for the machine. I don't remember how to install or set-up the file but plan to look at it tomorrow to try to figure it out.

    Thanks

  2. #2
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    Re: CNC 'jumps'

    I doubt that a crash like that would disrupt your software settings. But it certainly could throw bolted-on rails out of alignment. If there are suddenly a few places where the motion of an axis isn't smooth, that's the first thing I'd check. Without applying power to the machine, just roll the stage along the rails and see if you can detect anyplace where it's hanging up. If it's not that, check the couplers for looseness. This may not be apparent at first, so make a mark with a Sharpie across the coupler and shaft, and see if you notice any offsetting when this "jumping" occurs. Set screws can get into a condition where they hold on seemingly tightly, but then come loose and move a little on the shaft when stressed. If it's not the rails or the couplers, then it's probably some other mechanical issue, like a distorted frame or damaged screw.
    Andrew Werby
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  3. #3
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    Re: CNC 'jumps'

    Quote Originally Posted by awerby View Post
    I doubt that a crash like that would disrupt your software settings. But it certainly could throw bolted-on rails out of alignment. If there are suddenly a few places where the motion of an axis isn't smooth, that's the first thing I'd check. Without applying power to the machine, just roll the stage along the rails and see if you can detect anyplace where it's hanging up. If it's not that, check the couplers for looseness. This may not be apparent at first, so make a mark with a Sharpie across the coupler and shaft, and see if you notice any offsetting when this "jumping" occurs. Set screws can get into a condition where they hold on seemingly tightly, but then come loose and move a little on the shaft when stressed. If it's not the rails or the couplers, then it's probably some other mechanical issue, like a distorted frame or damaged screw.
    Thanks. I will check that out and report back

  4. #4

    Re: CNC 'jumps'

    you can make video of the problem and image of confs?

  5. #5
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    Re: CNC 'jumps'

    Overwhelming probability that it is a mechanical problem with the movement on that axis.
    We would need more info on the hardware.

    Cheers
    Roger

  6. #6
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    Re: CNC 'jumps'

    Well pretty sure I found the issue. Took about 2 minutes to find it...lol. Stepper coupler snapped. Just need to figure out what size it is and where to get it. Probably happened when my router stopped and the bit drug across the material and bound everything up.

    url=https://postimg.cc/WdWcYD7b][/url]






  7. #7
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    Re: CNC 'jumps'

    Those look like the aluminum helical couplers I had on a machine of mine, that did the same thing. I replaced them with Oldham style couplers - the kind with a rubber "spider" in between the two opposing halves, and a clamp-style attachment rather than the set screw - and haven't had a problem since.
    Andrew Werby
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  8. #8
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    Re: CNC 'jumps'

    Thousands of them on ebay.
    But I suggest you should check the alignment between the motor and the shaft. Those couplings are not all that fragile, so there must have been a lot of flexing to get that fracture.
    If the alignment can't be improved, then an Oldham or similar might be a better choice. A couple of dollars more - very trivial.

    Cheers
    Roger

  9. #9
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    Re: CNC 'jumps'

    I don't think alignment was the issue. I used it for years with no problems. My Bosch router quit working in the middle of a cut and it flexed pretty bad, which I'm guessing snapped that coupler. After I removed the motor today I moved the axis by hand and it was smooth.This is an aluminum t slot machine so it has some flex in it with any resistance. But i will order a couple of couplers so I have a spare. Thinking of selling the machine since I rarely use it anymore but wife wants me to keep it.

  10. #10

    Re: CNC 'jumps'

    I'm really surprised that the motor didn't stall before snapping that!

  11. #11
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    Re: CNC 'jumps'

    So any idea what the shaft size is on that stepper? Checked it myself and looks to be about 1/4" or maybe about 6 or 7 mm? Still need to find out what size the other end would be. Haven't taken the other end off yet. Will probably have to disconnect all my wiring and turn the machine to get in there to get it off. Not looking forward to that...lol.

  12. #12
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    Re: CNC 'jumps'

    Quote Originally Posted by DHay13 View Post
    So any idea what the shaft size is on that stepper? Checked it myself and looks to be about 1/4" or maybe about 6 or 7 mm? Still need to find out what size the other end would be. Haven't taken the other end off yet. Will probably have to disconnect all my wiring and turn the machine to get in there to get it off. Not looking forward to that...lol.
    This is quite a normal problem with these aluminum couplers don't replace it with the same type

    This type is the best for zero backlash Diaphragm Flexible Coupling or the double Diaphragm

    https://www.ebay.com/itm/10mm-to-14m....c100005.m1851


    https://www.ebay.com/itm/Clamp-Tight....c100005.m1851
    Mactec54

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