I have researched this topic here, in Facebook (Sculpfun/LED Diode Laser group) and in other forums and I don’t see any real answers… most of the posts end up closed with no response.
I am attempting to engrave images on a white tile and getting vertical banding. I have tried 318 dpi vs 254 dpi… halving the speed and power… rotating the image 90 degrees - I still get banding. I’m thinking it has to be somehow connected to the dpi because it does change with the dpi selection. At 318 dpi, the banding was at almost 2mm and at 254 it was 1.7. When I reduced the image size (in Lightburn) by 50% in each direction, still using 254 dpi, the banding was at about .9mm.
The only misgiving I have about it being related to dpi is - it’s only banding in the vertical direction. I would have expected more of a ‘moire’ pattern effect.
The reason for the half speed/power setting was in one forum, it was suggested that there may have been vibration involved. Considering it’s only in the X axis (vertical banding), that may not be so far off… as the X axis is travelling back and forth at speed and the Y axis is just moving one pixel at a time… Hmmm - seems like maybe more experimentation is in order.
You’ve done and posted lots of different tests to try to take this problem apart. This is Great, you’ve narrowed this down to only a couple of things.
254 dpi is for a laser dot that is .004" across. That’s about the thickness of a sheet of cartridge or heavy photocopier paper. I feel this may be optimistic for the higher output laser diodes. The most elegant tile work i’ve seen takes hours and is done on lower output diodes (or galvanometer lasers with even smaller dots).
I agree with what you’re saying about the Moire pattern. I believe that the rectangular shape of the dot is blending the scanned output and you’re not seeing the dpi error as easily in the horizontal direction. I posit that you’re getting light on 3 or 4 horizontal pixels as it scans and and 1.5-2 vertical pixels in some odd way that makes the error stack-up.
I’m looking at this, this way because the banding is narrower than the belt pitch and it changed when you adjusted dpi.
If you draw a square and engrave it at your current speed and power you can see the difference in the shape of the dot. The horizontal line will show the vertical height of the dot and the vertical line will show the horizontal width of the dot.
With those two measurements, set your dpi based on the thickness of the horizontal line (this may already be right or very close) then adjust the horizontal Dot Width Correction in the Cuts Settings Editor for your image layer. Dot Width Correction is in the middle of the pop-up window when you double click the Layer with your Image in the Cuts / Layers window.
If you get two different measurements out of the test on the square - please post them. I’d like to see what they are for the Sculpfun S9.
It could still be machine resonance but I’m leaning toward dot size and dot width correction first.