skew correction

Simone

i have done a first tes for the skew but i dont know if i did it right so i did another test with the precedet skew compensation activated Axis compensations - XY: -0.00146, YZ: -0.00305, ZX: -0.00146
the second test is giving me this number Skew factor: 0.0014215
Skew distance @ 99.4 mm: 5.981661 mm for XY

What i need to do i change the XY: -0.00146 whit 0.0014215 or i need to add them? im more confident using the second test diagonal measurement |the first wase the one whit the ruler
https://docs.duet3d.com/en/User_manual/Tuning/Orthogonal_axis_compensation

OwenD

@Simone
I presume you're using the macro provided on the page indicated?

It would be better if you specified the measurements you took for each value, perhaps with pictures.

If the skew is indeed 5mm @ 100mm then you need to fix the hardware misalignment, not try to compensate with software.

droftarts

@Simone I updated the documentation a while ago to include the second method, and it was then pointed out that the skew calculation output the skew factor with the incorrect sign. See https://forum.duet3d.com/post/307701

I was going to check it and update the documentation, but I forgot! But as @CalinFlorin86 pointed out, if the angle was acute (ie AC > BD) the skew factor should be negative, and if the angle was obtuse (ie AC < BD) the skew factor should be positive. I have updated the documentation to note this, and updated the macro so the output should be correct.

That the numbers you are seeing are basically the same (XY: -0.00146 the first time, and Skew factor: 0.0014215 the second time, though this should be negative), it sounds like skew compensation was not active the second time. Otherwise the print would be square, I think.

Ian

droftarts

@Simone I've updated the calibration macro again, so this time it actually works correctly! @OwenD was kind enough to point out the error in my maths, which gave NaN results in some circumstances, and checked that it now gives correct answers. See https://docs.duet3d.com/en/User_manual/Tuning/Orthogonal_axis_compensation#calculate-the-skew-factor

Ian