Radiused Corners, Only Opposing Corners Are The Same

Larger Format DIY Laser. Gantry Runs Left to Right. Ruida RDC6445S Lightburn 1.7.01

Recently upgraded laser tube, laser psu, 24v PSU and added an independent stepper driver where i had been running both Y steppers off a single driver. Updated to LB 1.7.01 noticed the issue comparing to older cuts made prior to any of the above. Upgraded to wider Y axis belts, it was in the plans but not for this issue, tensioned belts, pulley grub screws and rechecked E-steps on X and Y.

The issues I am having is that on a square with equally radiused corners, a slot and even circles, the upper left and lower right (opposing corners) are more radiused than they should be. Its as if those corners are starting the radius just a bit to early and need to relax the arc to meet the sidewall. The machine will retrace the same cuts over and over and is cutting great squares. I do not see signs that the gantry’s racked or steps slipping skipping.

Machine is cutting the below counter-clockwise. I exaggerated the radius. It appears to be approx 2-3 points greater than requested

Any suggestions?

Looks like backlash. You could turn on hide backlash… it will help in some cases, but not for closed shapes like this.

How large? I’d look for twist/rocking in the gantry from front to back when it changes directions in its Y axis travel, although if it’s only the top left and bottom right corners – and not the top right and bottom left corners – it may more likely be backlash in the X axis… look for rocking of the laser carriage.

64x36inch Gantry length is about 42inches. Ill look into backlash but didnt think that would impact circles in the same way. Slowing Speed and acceleration doesnt seem to impact it to show up visually. Is there any calibtration built into lightburn for setting backlash in cuts like their is for engraving?

Backlash will definitely show up in circles… it’s where you’re most likely to see it when just cutting shapes on their own. The other places you’ll see it is shapes like squares not quite closing, or things not quite lining up when marking/cutting multiple elements individually and moving back and forth between them.

I would not be surprised if twisting or rocking of your gantry and/or carriage is the culprit rather than backlash in your belts.

I also expect that a picture of your results would look a little different than what you sketched. I’m presuming that one end of the radius curve is a little ‘longer’ than the other.

Thanks. I will try and read up on backlash some and go from there .

As far as gantry rocking, nothing has changed and the carriges are snug. So backlash maybe my best start point