Using a roller with very light pen casings. Have put a longer shaft in the casing to add weight against the rollers. However the whitespace speed is shifting the casing on the roller hence the burning image shifts. Have enabled whitespace scan and set slower mm/min ie 500 but this appears to be ignored. Any help appreciated. Using a creality cr falcon laser with GRBL Cheers
The rotary is likely rotating at the same speed as your scanning operations. Test this by slowing down your Cut settings.
There’s not a Cut setting that you can use to arbitrarily change rotation speed. Here are a few remediation techniques:
- You could force Y-axis (or whatever axis you’re using to control the rotary) to a lower max acceleration and speed in your GRBL configuration. $121 and $111 respectively for acceleration and speed on Y-axis. You’d want to change this back and forth when doing rotary vs flat work.
- Further increase friction by adding weight or some other mechanical method
- Consider switching to a chuck based rotary. This would avoid the slipping issue entirely.
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GRBL-ish controllers have a separate speed for whitespace in Device Settings:
However, a roller rotary doesn’t have a lot of traction on a pen, so even moderate speeds or hard acceleration will cause slippage when you can least afford it. Proceeding at a stately pace may be the best it can do.
Remember: speed kills! 
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This needs to be evaluated for each object type. The problem is there is too much acceleration for the mass of the pen. Adding mass to the object to get better driver roller contact sounds good, but it’s compounding the problem.
All of these have some kind of balancing act to find the best speed/acceleration for the amount of added mass and how much traction you get.
I have setting files with different names that set the acceleration value for the Y axes to a lower value and a lower jump off speed… This is what speed the motors start to turn. All I need to do it read the existing data in and write it to the controller.
This pretty much means, at least to me, that vector engraving on mugs should be kept to chuck type rotaries. Wheel or roller types really slip around if you try using a vector.
I have both a PiBurn (expensive) and an M80 chuck that came with my fiber machine. I use them where I need them. Either works for either machine.
As @berainlb advised, you might have less headaches with a chuck type rotary.
Good luck.
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Thanks for your reply Will try changing the GRBL file to incorporate those settings. Have added weight and it does help considerably. Yep need to get a chuck for this type of work.
Your point re the vector file is correct. Since its a black and white I will change it to a JPG image and that will stop it whitespacing. Good call.
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Creating an image rather than vector sorted the issue. thanks all