I discovered the hard way that setting Start from Absolute Coords means starting with a G90 and then using G91 for the rest of the job, not using G90 throughout the job. So when I paused my 4 hour print to finish the next day and used OctoPrint to raised the Z axis, it reset G91 and therefore everything is getting printed around (0,0).
Is there a way to set LightBurn to avoid using G91? (I’ve looked but don’t see it in the UI or docs.) If not I guess I’ll need to write a post-processor for what I want.
Relative coordinates are used for fills and raster engraving because the GCode tends to be smaller, and therefore processes faster. Why would you need to move anything when you pause?
I moved Z up so I could see the progress then lower it again. Octoprint turns that into
G91
G0 Z100
G90
G91
G0 Z0
G90
so you can see why it would mess up the rest of the print (as the GCode has a single G91 in it).
I ran it through a post-processor to force the coordinates to absolute, then truncated the first 11000 lines to pick up where I left off.
I guess I’m just used to absolute because the other CAM softwares that I use use them by default. It is handy if you lose a step or anything else that might ruin a job. You can reset your origin and pickup where you left off.
If you weren’t engraving photos, absolute coords would be ok. If you are, the amount of extra data sent is significant enough that it could affect the streaming rate.
The latest versions of LightBurn allow starting a job from an arbitrary point in the preview window, which is how we handle picking up where you left off, and it works for systems that aren’t GCode based, too.