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IndustryArena Forum > Machine Controllers Software and Solutions > PlanetCNC > Fixing gantry skew through machine settings?
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  1. #1
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    Fixing gantry skew through machine settings?

    I've built a fairly wide CNC machine and there's a small skew in the gantry which would be easier to fix, I think, via the transformation settings for the machine. I adjusted the values in the settings and it works correctly while running a program but I would like it to also work when jogging the machine manually or in any other mode, that is to say, to bake in the skew adjustment. Is this possible?

  2. #2
    Community Moderator Jim Dawson's Avatar
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    Re: Fixing gantry skew through machine settings?

    While many times it is possible to compensate, in software, for minor machine mechanical deficiencies, there is no substitute for having the machine mechanical systems adjusted correctly to begin with.
    Jim Dawson
    Sandy, Oregon, USA

  3. #3

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    Transformation and points values can be addressed thru scripting.

  4. #4

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    Re: Fixing gantry skew through machine settings?

    I do not understand exactly what you mean.
    I do a gantry squaring after turning on the machine. After that it doesn't matter whether I move manually or whether a program is being processed.

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    Re: Fixing gantry skew through machine settings?

    The machine is based on the OpenBuilds OXCNC, the gantry is 1.5 meters wide and it's driven by G3T belts so as you may imagine is not very rigid, specially when it's turned off and the Y axis motors are disabled.
    When it's off and the gantry is moved it comes out of square, so what I do is to move it against temporary blocks on each side of the gantry before turning it on, run a pointed bit along the edge of the table to check it follows along and if there's any difference between X 0 and X 130 I can remove it with the transform settings.
    The problem is that those apply only when running a program, so for example now I'm using the machine itself to cut the three piece table from HRM board, I cut the rectangular pieces first and then need to place them on the table to drill the mounting holes, hold down nut pockets, etc. It's easier to place the material for cutting down in reference to the machine frame, but if there is a small skew along the full length of the X axis travel (usually is 1mm or less) then it becomes complicated to align things since I would need to calculate the angle the work piece needs to have in reference to the frame. It would be easier is I could put down the board and place the cutter over a couple corners to verify it's in the right position.

    Ultimately what I'd like to have is four calibration holes on each travel limit of the table so when the machine is turned on and set up I could jog to each corner and verify everything is square, the alternative work around is to have a simple program drawing a rectangle that moves the head to each corner, but it would be simpler and less prone to errors if the transform would always be on.


    Actually, I thought that a better way would be to be able to control each Y motor independently for adjustment, so the procedure would be to turn on the machine, move it to the X0 Y0 calibration mark and zero it, move it to the X0 Y130 mark and zero out any misalignment in Y by moving a little the right side motor only. Is that something that could be done via scripting? Having two paired outputs with a manual offset control to adjust the gantry angle, that would be nice.


    The machine is 5 axis meant to cut light materials, in particular to cut PVC foam boards. It's both a prototype for a larger machine I'm using to make a scale prototype of what I want the larger machine to cut, the larger machine will be used to cut composite foam sandwich panels for a boat project I've been working on for a couple years. The idea being that I can CAD all the components, make a 15% scale model to make sure everything fits as it should and then when everything works I can move on to the real thing, I may have to rent a space to do the full scale job so it's better if everything is worked out beforehand.

    By the way, I'm using MKS Servo42 Closed Loop controllers on the A and B axis motors, they work great but it would be even better if the controller could communicate with them, I've been meaning to open a thread about that.


  6. #6
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    Re: Fixing gantry skew through machine settings?

    Quote Originally Posted by Jim Dawson View Post
    While many times it is possible to compensate, in software, for minor machine mechanical deficiencies, there is no substitute for having the machine mechanical systems adjusted correctly to begin with.
    For this machine, it really is the opposite case.

  7. #7
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    Re: Fixing gantry skew through machine settings?

    Quote Originally Posted by tantemay View Post
    I do not understand exactly what you mean.
    I do a gantry squaring after turning on the machine. After that it doesn't matter whether I move manually or whether a program is being processed.
    You do the squaring by software or physically?
    I can force the gantry into position by pushing one side and making the stepper motor jump, but the it moves in approximately 1mm steps, which is a bit coarse.

  8. #8
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    Re: Fixing gantry skew through machine settings?

    Quote Originally Posted by SkiPatrol View Post
    Transformation and points values can be addressed thru scripting.
    Good to know, I didn't get into the scripting side of the controller, but I guess I'll have to jump down that rabbit hole.

  9. #9
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    Re: Fixing gantry skew through machine settings?

    Hi CO - I am thinking about a 5 axis machine at the moment what CAM and machine controller are you using? Is that side working out? Peter

  10. #10

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    Re: Fixing gantry skew through machine settings?

    As I said, I won't get over your problem. TNGv2 can do exactly what you want, align the portal at a 90 ° angle to the machine bed axis.

    https://m.facebook.com/watch/?v=433234400943430&_rdr

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