I still maintain that the result is exactly the same as the onscreen version you posted earlier. The onscreen version is a badly drawn circle, and so is the result.
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Has nothing to do with it unfortunately. (Thought I mentioned earlier). The preview is just that, a rough preview to save on display resources and has nothing to do with the drawing.
I know it was mentioned earlier, but errors in the bitmap are directly visible in the finished cut.
The quality of that bitmap circle is not consistent with any attempt to save display resources or draw circles more efficiently. They weren’t drawn that badly in 1984 on a 128K Macintosh.
That may be so regarding the Mac, but that’s how it is regardless.
The new belts and pulleys are supposedly coming today 
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Best of luck! I hope it fixes things for you.
Essentially this Fusion360 drawing shows it better exaggerated: (Y axis is much less because there’s two belts) I actually think I’ve seen this when people put a J tech laser engraver on their Shapeoko and don’t get great circles: Shapeoko Pro and 4th Axis / Laser - #7 by AsylumWoodworks
Can you export a DXF or something from LightBurn just to rule that out?
Was that drawn in Lightburn? I know DXFs get weird sometimes, but I see a lot of nodes. I wonder if a “better” circle might help with the motion control?
As you stated, the DXF definitely does not show any flats.
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All circles are broken into line segments when sending to DSPs. If I import our DXF parts drawn from Fusion, there would be no change when it sends it over to the DSP.
So given the line segment nature, have you checked for a circle tolerance setting in light burn? It’s still seems weird that it would only apply on the orthogonal axis, but it might be combining with some other rounding behavior.
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Yes, that has been previously mentioned. Changing the arc tolerance values from 5µM to 100µM didn’t change the cut quality.
Still waiting on UPS to show up with the belts.
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Just to silence the crowd, maybe you could rotate the circle 45degrees as this would show that it is the machine, not the design
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Ok, missed that. So based on that and your step testing it’s probably not exceeding machine resolution (too detailed/too many steps, in some segments you end up missing detail due to comms issue or rounding). Still feels mechanical, though it would be nice to have a compensation in software.
I’m actually hoping it’s the machine, which may sound weird! (please don’t be the linear carriages) 
I forget, did you ever drop to 1/8 microstepping?
Yes 
I can say it isn’t very fun taking the rack enclosure in and out. Getting too good at it, sadly…
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Here is a comparison of the stock pulley and belt vs the new pulley and Gates belt:
The original belt feels like a wet noodle in comparison! 
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Nice! How many teeth in the pulley?
24 teeth was the minimum available so that’s what we got.