Cylinders are small but Cubes are accurate

I’m new to Bambu and don’t know what to expect in terms of dimensional accuracy. After printing several square/rectangular parts, I calculated my shrinkage value to be 99.4% for Polymaker ABS, red color. The ABS was dried before testing and has been sitting in the AMS2 at 7% humidity.

The round section of my part is consistently too small but the square portion is dimensionally correct. How do I make the round section bigger without affecting the square section?

I’ve tried:

  • Changing the shrink factor (makes the square too big)
  • Auto circle contour hole compensation (not much difference)
  • X-Y contour compensation (makes the square too big)
  • Slower print speed (made problem worse)
  • Bigger in CAD model (best solution but harder to manage)


I see other folks mentioning the same thing at:
https://www.reddit.com/r/BambuLab/comments/19clhfh/dimensional_accuracy_off_in_circles_not_squares/

https://github.com/bambulab/BambuStudio/issues/3972

https://www.reddit.com/r/BambuLab/comments/15kw4oc/bambulab_p1p_dimensional_accuracy_issue/

I believe contour compensation is what you’re looking for

https://wiki.bambulab.com/en/software/bambu-studio/xy-hole-contour-compensation

Thanks, but as I mentioned, I already tried that and listed the results in my table.

Oh you’re right, I completely glossed over that, my apologies

It seems the issue may be with Bambu Studio’s gcode and not the H2D. I posted more information on the other thread.

Yes it’s gcode issue. Basically arc fitting is trying to make up a circle while it’s actually a lot of connected points. And then it has to apply shrinkage compensation (if you have done any). Lots of different things altogether.

I’ve done a lot of analysis on the gcode generated by Bambu Studio. The arc fitting function is inconsistent. Details are in the Bambu Studio thread I posted above.

Which did you use for a model file type, a STEP, or STL? I assume STL due to the number of faces in the screenshot. If correct, have you tried using a STEP file, or any file type that support an arc?

I used 3mf out of Solidworks.

I just imported as STEP and used 0.01 for the angle deflection. This created lots of triangles. The Arc fit generated two arcs and short linear section.
The two arcs were still 0.69% smaller than a square in terms of gcode steps/mm.

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submit this on github maybe

Thanks. I just found the Github repo and submitted it there. Bambu’s support ticket response was completely unhelpful.

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