Rotation is helpful on several fronts- one, it prevents lines from building up artifacts. The existing texture left from a prior pass can affect how it reacts to the next layer. In a way that the deepest part of a groove absorbs more that the peak, so it doesn’t smooth out, it deepens irregularities as it goes.
You do get some odd artifacts with long, thin, straight line features that line up with the raster axis. If you’ve got a 0.05mm line with a 0.03mm stepover, it may resolve as 0.03mm wide or 0.06mm wide where parallel to the raster axis.
It would make sense if Lightburn did interlacing, like NTSC TVs used to do. That is, the even passes would be a 0, 0.03, 0.06, 0.09.. then the odd would be 0.015, 0.045, 0.075,etc.
But rotation does basically the same thing, only better.
But I have wondered about the best rotation number. It’s nitpicking, but if you use 45 deg, a pass overlaps exactly with the one 4 passes prior. And there can be some very slight artifacts where the features are cut from 4 directions and not infinite.
So, I got into the habit of making up a randomly odd-ish number like “47.2” deg so that it won’t make identical repeating sets of 4 passes. I can get some great high detail work, so I must be doing something right.
But I had to wonder, is there a “best” number that doesn’t overlap even over many passes? I asked chatGPT and it went through numbers theory and coprimes and had a solid suggestion, knowing that Lightburn only lets you specify in 0.1 deg increments:
42.7 deg. It’s “basically” 45 deg=4 directions bidir/8 unidir (but it’s pointless to use uni since you’re going to come that direction anyways, it’s just a waste of time to use that limitation).
But it won’t repeat for 1800 passes. And after only 20 passes, the drift on these ~45 deg steps will pass the 45 deg of drift, it crosses over itself. So basically as close to “all the angles” that would be possible.
If your intent is ~90 deg (cross-hatching) the passes, then chatGPT had several suggestions and I like 90.7deg the most.
So, write these “magic” numbers down. 42.7 deg if you want to hit “all the angles”, or 90.7 deg if you think ~90deg “cross hatching” will be better
I used that on not only 3D engraving but cutting out microscopic tools out of razor blades with great results. I made finger joints in the blade where the gap has to be the thickness of the blade. Didn’t run 45 deg head-to-head with 42.7 deg though.