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Thread: one corner of rectangles bad/ splayed out

  1. #1
    Join Date
    Feb 2020
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    3

    Default one corner of rectangles bad/ splayed out

    Cant seem to cut perfect squares... its always the 4th corner near the end point of the cut - cut splays out or in.
    motors are tightened and offset bearings are tight - no movement from xy car on the gantry.
    overall i get slight jiggle on all axes but I think this is normal?
    thought it was something to do with the de-acceleration tried cutting using several methods to avoid that with no luck..
    happens on first pass, so this rules out slipping parts or tabs problems.

    IMG_20200221_144512611_2.jpgIMG_20200221_163535_01.jpg

  2. #2
    Join Date
    May 2014
    Location
    MA
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    580

    Default

    overall i get slight jiggle on all axes
    I think that's your answer.

    How much play are we talking about? Have you measured it with a dial indicator?

    Also, what machine are you running?

  3. #3
    Join Date
    Feb 2020
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    running a prs standard. it appears after tightening the motors in place the gantry can move almost .01 according to the dial indicator..

  4. #4
    Join Date
    May 2014
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    MA
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    580

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    .01" is high. If you figure that your gantry has one motor at each end you've got a combined .02" of slop, and that's after you tightened things up. I'd check for worn pinions first as they're a wear item, then I'd look at your gearboxes. As those get older they get backlash in them as well.

  5. #5
    Join Date
    Jan 2004
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    Novato CA
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    214

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    Don't forget that these pinion gears often have two set-screws in each threaded hole, one on top of the other.

  6. #6
    Join Date
    Dec 2005
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    Pro Signs, Coal CIty IL
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    Default

    If that cut was made with a 1/4" bit, that's a lot more movement than just a few .01".

  7. #7
    Join Date
    Feb 2020
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    Default

    the cut was made with a 3/8 bit

  8. #8
    Join Date
    May 2014
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    MA
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    If there is slop the machine will move no matter what bit is in there.

    Dial out that slop if you can.

  9. #9
    Join Date
    Dec 2000
    Location
    Thorp, WI
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    2,783

    Default

    Along with that, something you can try in your design file, is to uncheck "Sharp external corners". This helps to keep a slight load on the tool as it makes the corner instead of a stop/start right angle path that unloads and loads the tool abruptly.
    Scott

    "It’s easier to fool everyone than it is to convince them they've been fooled" - Mark Twain





  10. #10
    Join Date
    Oct 2000
    Location
    Willis Wharf, VA
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    Default

    Have you tried making changes to your toolpath to see if it helps? Do you do a ramp to minimize the amount of material it's cutting as it gets to the end of the pass? Or maybe try moving the start point away from the corner and along one of the sides?

    Bill

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