It is possible that you have simply found the resolution limit of the simulation you are living in…
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I find the segmented radius attractive. A digital and/or mechanical artifact. When I can, I resign from media blasting pockets and the like too, I enjoy the fingerprint. I can make something organic with my hands.
@LiamN : I still think this is unlikely, otherwise people would not be able to get smooth curves in e.g. metal, and they do. Something is off with my CAM or machine or both. We’ll know soon enough when Neil or Jon confirm what they see in their cuts. I am probably in for a facepalm moment when this is over.
@Lowbrowroyalty: it does have an interesting look, but to be honest at this point I’m more interested in understanding/finding why this happens than in the resulting piece.
I recorded an air cut, and one can hear/see the vibration/slightly jerky movements when doing the curves:
EDIT: aaaaand I realized I still had my “tolerance” at 0.0025mm, which is the reason for the many short moves & arc. I just did the test with another extreme, 0.5mm tolerance, the file has much fewer arcs and they are larger (of course), and the air cut sounds much smoother.
I’ll try a cut tomorrow with a very large tolerance like that to see the effect on the finish, for the sake of testing.
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yup, but not because
It is irrelevant because the G1 moves make straight segments. The lengths look to be about 0.2mm. The arcs are much, much smaller, and likely at the 0.02mm broke to only a couple linear, but at 0.002 would have broken into more, but the arcs are so small in angle as to make it pretty much not meaningful.
I see that boosting the tolerance helped. Good deal.
I don’t know why Fusion would put the straight motions in between the arcs. It is not hard to fit the arcs without them for most ways of defining the curve.
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I will have to look at this tomorrow evening as i need to break a project to get acrylic lol see what i do for science!
Also check this out, i was looking at a Fusion 360 vid - more training again :), but this part i think might be worth doing on your model Julien, it may make no difference but as he says this then confirms to G1 and G2 - interesting, it may be applied when you did the normal spline but worth a try, Fusion 360 constraints explained with examples fantastic vid would recommend to watch from start, but bookmarked at right location
Jon
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Pretty cool, I didn’t know about that! Interesting feature to use when there are no specific constraints on the shape
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Far from a diversion this is turning out to be rather interesting in terms of how the design gets turned into machine movements.
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it’d not be insane hard to make a small tool that, say, takes a circle diameter, depth of cut and number of segments, and turns that into some gcode
…
should make it sort of easy to see if this is digital or mechanical
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Have you compared the pitch of the belts to the the “pitch” of the lines in the plastic? Your belts could be stretched and not meshing with your sprockets smoothly but sort of snapping into the sprocket as it turns.
Cheers
Mike
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Acrylic is unforgiving.
No matter what I try, I get those marks. I did a redesign of @Julien’s spline design and just used tangent arcs and lines. Same thing.
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@fenrus, I’m sure by the time I’m writing this response, you have already implemented this ? 
@JappieMike the pitch of the belts is 2mm, they may be stretched by a few percent,so not a really good match to the ~0.5 to 1mm periodicity I see, also it would very likely show in the “X only” and “Y only” moves too, and it doesn’t. That said, I had in my list a test where I would purposefully untighten my belts to see if it changes anything.
@neilferreri thanks for the test cuts, appreciated ! I’m a little relieved that it’s not only me, but even more curious as to what is going on there. Does your G-code has the succession of very short G1 segments and G2/G3 moves too? I’ll redo a test cut with a pure circle later today (basically a single G2 command) and see if it changes anything.
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No. As soon as I saw that with yours I thought, “well, that’s the problem”. So I tested and I still got the same edges. 
I’m horrible at documenting (not good for this sort of thing), but I tried a number of different settings with tolerance, both in the CAM settings and in the user options when post processing. I changed the $12 values.
It was actually pretty frustrating. I could only seem to make it worse.
I think I saw signs of what I could only guess was from deflection.
Start fundraising for that 600fps camera… I’ll chip in!
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So, no rules about bad puns on the forum then?
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This is why I really want to see a physics-based simulation which actually takes into account flute geometry — could this be some sort of interaction between how quickly the endmill is turning and how quickly the machine is moving the endmill against the surface?
Rather brings the significance of SFM into focus.
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What I really don’t get is why this seems to happen specifically in acrylic. Either it happens all the time and it’s just much more visible in acrylic (but then I would expect to see it in aluminium), or as you say it is some kind of interaction between the cutter and the material (something like the cutter “pushing” material in a tiny wave in front of it or some other exotic phenomenon).
If this is actually a material/cutter interaction, then there is hope to find the right recipe to minimize it.
Maybe I should come up with a prize for whoever explains this in the most convincing way!
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It might be worth trying a polycarbonate or other transparent plastic to see if it’s a property of the Acrylic when cut?
HDPE is so very different as a material but it might be worth comparing the finish on that?
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sorry @Julien i only had enough for one cut, Lets just say mistakes where made ,you can look at the results of it, once i piece it all back together currently evenly distributed about the workshop, not able to hold it down with clamps and apparently my new super double sided tape is "£$"£% thus i took the cut to the molecular level!
I am all out of stock sorry, but i feel i need to do something to help you on this crusade so i will #holdyourbeer
Jon
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I would say that I’ve seen a similar thing on any plastic I’ve cut (acrylic, HDPE, polycarbonate, PVC, abs). I always attributed it to the single flutes I tend to use and it never really bothered me until late last night when it drove me nuts.
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If you stack some cut pieces on top of each other, do the imperfections line up?If they do I’ld say it’s the code or the tool, if they don’t it’s probably something in the machine.
Cheers
Mike.
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