Vertical banding when engraving horizontally

Machine:K40
Board: Cohesion 3d LaserBoard

Firmware: Smoothie cluster firmware

Problem/ Question:

I haven’t used the machine for some time now but when I went to use it I’m getting vertical banding on acrylic, seemingly only when engraving horizontally. I’ve made 1" square and engraved it at 0 deg in Lightburn and I end up with vertical bands. The banding appears wider & further apart if I increase the speed from 100 mm to 200 mm. With only changing the direction of the scan to 90 deg in Lightburn the bands are not there leaving all other settings the same.

I’ve cleaned & aligned the mirrors and adjusted belt tension on the X axis. I’m looking for a direction for other potential places to look. Thanks in advance.

Post some pictures of what you’re seeing and the settings you’re using in lightburn to achieve those results and i’ll give some advice on hopefully how to fix it.

Thanks Loather, any advice is appreciated.

Here’s some pics of what I’m seeing. I just created a new file, created 4 squares with 2 at 100mm/sec and 2 at 200mm/sec and 2 of them are engraved on the X axis and 2 on the Y axis directions. Each labeled to try to indicate what direction / speed they were run. I created the job and only sent 1 square at a time, disabling the other 3 then ran each job independently of the others.

And here are the screen captures of the settings.

If there’s any other info I can provide to assist in resolving this just let me know. Thanks again.

This is definitely an odd problem. I thought i might be able to narrow it down to PWM issues or something by looking at those photos but it’s too regular, and seems to be harmonic with the speed so it’s something related to timing. i’ll have to think on this one for a bit.

Try offset fill - i’d be curious to see what that looks like.

Here’s offset fill at both 100 & 200 mm/sec. Not the results I expected to see for sure. idk

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