Calibration

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  • March 25, 2015 at 1:48 am #7572
    Zootalaws
    Member

    I am having some strange issues…

    My machine was calibrated fine, until I loaded the new firmware and splatted the config.

    Now it’s a piece of poo…

    So, I went back through the process I was using before to calibrate it, but I am getting funny results – although it could just be me…

    I am using Gates GT 3mm belts on a 20-tooth sprocket, so in theory the distance-made-good-per-revolution is 60mm, but it isn’t – it’s 63.25mm

    And every time I measure it, it seems I get a different reading. So I adjust the mm/rev and zero the axis, move the axis 100mm and measure – and a different measurement.

    I am losing my mind. I did have a copy of the config that worked, but it seems to have gone west.

    Other than step angle, microstepping and mm/rev, what else can affect the distance travelled?

    I am measuring the distance using a digital rule that measures down to thousandths of a mm, but I am only taking 2 decimal places.

    March 25, 2015 at 1:53 am #7573
    Zootalaws
    Member

    FWIW, the process I use to calibrate is:

    Set mm/rev to 60.

    Move gantry 60mm

    Measure actual distance (55.91)

    Take 60 and divide by 55.91 = 1.073

    Multiply 60 by 1.073 = 64.38

    Change the rev/mm to 64.38, repeat.

    The last time I did this I needed three passes to get G0y100 to equate to 99.99mm actual movement. Now, it seems to go backwards and forwards and I have done it about a hundred times and gotten different results each time.

    Could it be something mechanical?

    March 25, 2015 at 7:18 am #7576
    cmcgrath5035
    Moderator

    Someone recently had a similar situation, reported back later that he found set screws has loosened on pulleys, just enough that shaft could slip between nicks from the set screw cup. Worth a check I suppose. His was a NEMA23 machine as well, IIRC.

    7% seems like a rather large error, I would agree.
    And variation is worse than fixed (static) error.
    Same error in X and Y?

    I assume your fw change was from 435.02 to 440.14 ?
    I recently updated my NEMA 17 machine ($xtr=36.54) and have run several jobs that seemed OK, but did not get out a ruler and check; I’ll do that.

    report – I just Zeroed my machine at one end and made 5 sequential 100mm move in Y. based on quick measure with Scale screwed to side rail( not as accurate as yours, for sure),accuracy of each move good to at least 0.5% with each move and overall.Then G0 Y0, then G0 Y500; no observable error.

    If you make a slower move, see same error? Perhaps too much jerk?
    I am running with $yvm=16000 and $yjm = 5000

    I am running with $xpm (power mgt) =3 and $mt=10 sec

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