My circles are coming out too big?

[Reloscott (Scott Gerami)]

Hello! I recently purchased Lightburn and it seems to work great. However, I am having a strange problem when cutting circles. for example, If I want a 23 mm circle it cuts 24.24mm? I calibrated the X & Y and when I cut out a 150 mm square it is almost dead on. 150.14 mm I can’t find any additional documentation on this issue other than calibrating the X & Y. Any suggestions will be very appreciated.

I am running an Openbuilds 1515 CNC(Black Box/GRBL) with a Opt Laser Diode Laser( High-Performance OpenBuilds LEAD CNC Laser Upgrade with PLH3D-6W-XF+ and LaserDock)

[ednisley]

@Reloscott

when I cut out a 150 mm square it is almost dead on

Did you take the cut width into account? If not, then the calibration will be incorrect because a “150 mm” square will be too small by the width of the cut, so adjusting the step/mm calibration to make it the correct size will make other sizes come out wrong.

A previous discussion explains the situation:

Kerf offset and calibration. What comes first?

I have a question about calibrating my diode laser. Perhaps I’m misunderstanding something… Let’s say that I calibrate my machine as per the lightburn documentation. After a few iterations of the process my “requested” and “actual” distances are suitably close. But they shouldn’t be the same because of the laser’s kerf. So am I supposed to run the calibration with the kerf offset activated? Because then the calibration is only as good as my measurement of the kerf. Or am I overthinking this? A…

If the machine has mechanical backlash, then all bets on calibration are off. Scale this test pattern to fit the platform and run it as fast as it will go in Line mode with optimizations turned off and power set to mark cardboard:

GrundTest.lbrn2

Any distortion in the results on the cardboard indicates a mechanical problem.