X/y calibration problem

  • I'm struggling to get my x/y calibrated. At 80 steps per mm, I am about 1mm shy of 20mm cal cube. z is perfect. On my Smoothie board, I adjusted the steps to get to the correct dimension, but when I do that with the Duet, I get a bed crash because the calculated value of x/y (84.1mmsteps/mm) lengthens everything. If I recalibrate the z length, keeping z at 80/mm, it's a mess with bed tilt, height, etc. So - what dimension(s) am I off on? I am currently at R256, L440 and bed radius 156… and just enough knowledge to get me into trouble, but not solve my problem. TIA!

  • Your steps/mm should be analytically known. This is given by tooth pitch or leadscrew pitch. Scaling this linearly to hit a single point error is not the right thing to do.

    In all likelyhood your calibration cube deviation is not due to a linear deviation from the analytical steps/mm. (Hard to imagine any mechanism that would give rise to such an error)

    More likely sources for the error is overextrusion or artifacts from slicing. If you are satisfied you are extruding correctly try to look for horizontal compensation settings in your slicer. This will take off some fixed amount from all dimensions, and not scaled to the dimensions size. (I.e. a -0.2mm adjustment scales a 20mm cylynder to 19.6mm and a 40m cylynder to 39.6mm)

    If you want to verify to yourself that you do/do not have a linear error try to slice your cube at 100% and 200% scale and print with the original 80 steps/mm setting. The likely result is that both cubes will be off by the same amount (or close to it) which indicates that a linear compensation is wrong. If however you find a 40mm cube is 2mm off while the 20mm cube is 1mm off, then you should consider scaling, but as I stated, this is unlikely.

  • On a delta you cannot calibrate the X-Y Dimensions by useing Step's /mm you need all towers to be the same so 80 in your case and adjust the rod length to get the x-y correct and all the steps/mm on the towers to get the Z Correct IIRC if you cube is small in the XY then increase rod length and vice versa

  • Thank you @Dougal and @sverreb - I went back to square one. The printer is a couple of years old and has been through many iterations at this point. I was still using the original numbers so everything needed a careful review. After a day of mind numbing experiments, I am close enough to print once again though will have to do further tweaking to get it as right as it should be. I appreciate the help I get here and in other forums, but nothing teaches me better than figuring it out from sources online and my own bull headedness. At this point, I can more effectively utilize your suggestions - thank you!

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  • No @dc42, I hadn't. Very helpful for the last bit of tweaking! There is a vast amount of gcode I haven't yet seen!

  • I suddenly have the same problem with my Delta. Z is fine but X and Y are 5% too small. I noticed it today running 1.19 and is still a problem running 1.20 firmware. Microsteps are set correctly.

    What could be the underlying cause of this? De printer calibrates using 6 factor calibration and 10 points to 'after 0.038'.

    I also checked the gcode, it uses the expected X and Y dimensions.

  • Problem found: rod length was incorrect. The config-override contained an incorrect length (+8%). Since I use 6 factor calibration this value isn't adjusted. It was probably a side effect of a 7 or 9 factor calibration experiment.

    What I learned: On a delta, if both you x and y are off by the same amount but your z calibration is fine. Take a look at the L parameter of the command M665 in BOTH config and config-override.

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