Need help reproducing a cut speed bug on Proofgrade . Anyone have Thin Leather? [RESOLVED]

THE LATEST: No need for extra test cuts on Proofgrade, @dan has verified that something may not be right, and sent the repro case to the engineering team.

Can someone try cutting the 1" diameter SVG below on Proofgrade Thin Leather, and see if it comes out as expected, or if some of the circles aren’t cut correctly? Thanks in advance for your help nailing down a Proofgrade repro for the support forum!

A couple of days ago I found what I believe to be a bug in how the Glowforge does some cuts. That thread is here, but I am starting this new discussion because I think the nature of the bug repro task has changed, and I need help.

(I believe the first report of this bug was in this thread by @wanderingwood but it was one of several topics in that thread and didn’t get the attention it deserves now that I’M the one having trouble. :wink: .)

Here’s the observed problem: If you have an SVG file with an array of circles, some of the circles may be cut at a speed higher than the speed you set. However, the bug only seems to manifest at high cut speeds, and no currently-available Proofgrade materials use a cut speed as high as my tests on cardboard.

My test object is a 1" circle with 3mm circles inside. It was made by hand in Illustrator CC 2018. (I have no idea what the root cause of the issue is, but I have tried a couple of similar files and triggering the issue was easy both times.)

Zipped SVG: Circle Cut Speed Test 1

When you cut this shape at 500/70 on thin cardboard, some of the circles get cut too fast, meaning too little power hits the material, meaning some of the circles are just scored and don’t drop free.

  • As noted in the caption, I was able to induce a change in which circles were mis-cut by reloading the app, reloading the same SVG, and cutting again.
  • In addition, copying a “good” circle over a “bad” circle in Illustrator and loading the modified SVG into the same session does not change how the file cuts.
  • If you watch the machine work, the speed-up at the poorly cut circles is extremely obvious. The extra head speed shakes my Glowforge table!

I thought this would be easy to repro on my scrap Medium Maple Ply, but it isn’t! The Proofgrade cut settings for MMP are 168/Full. 168 is a LOT slower than 500. If you watch the machine work, I believe you can see the head speed up a little bit at times, but the magnitude of change is less than I see on the cardboard tests at speed 500, and so the power delivered is still adequate to cut the material.

The fastest cut speed I can find for a Proofgrade material is Thin Natural Leather, 246/71. If I lie to my Pro and tell it I am cutting Thin Natural Leather, I believe the head speed aberrations are easier to see than cutting Medium Maple Ply at speed 168.

I suspect that were I to cut the test object on Thin Natural Leather, the problem with poor cuts might manifest. If anyone has a 1" diameter scrap of Thin Natural Leather, can you give it a try?

I assume it is important to reproduce this issue on Proofgrade if we want support to officially address the problem.

My guess is that there is some kind of bug in the head movement routine which increases in magnitude as the speed setting increases, meaning the effect is reduced or undetectable at low speeds.

Why it is easy to reproduce with circles, I don’t know. Thinking back to other things I have done at high speed, I bet this issue happens with other shapes, too… I’ve seen poor cuts I couldn’t explain alongside good cuts in the same high cut speed paper project.

We also routinely see “my Proofgrade didn’t cut through!” posts and so I wonder if some of those complaints stem from a related issue. Most of the time, material warping and dirty lenses seem to blame, but maybe there’s another issue, too.

Thanks for listening. I do love a good bug hunt… though, not as much as when a bug gets squashed.


I’m shut down for the night but will be happy to play in the morning if you don’t get any other people interested. This looks interesting :slight_smile:


I remember discussing this at the office! We thought we saw this behavior but couldn’t reproduce it - I don’t remember the circumstances.

I threw the file onto a machine at the office and then looked at the pulse file - it appears, to my very untrained eye, to be just as you describe; some circles are faster than others. I’ve passed along to engineering to take a look at it.


Woot, thanks for the assist!

Also, get out of the office and reclaim your weekend. :slight_smile:

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I’m not in the office. :slight_smile: Benefits of web interface… my lovely wife is working out before we watch a movie, so I have a little time to work.


Well done, great gamma testing! You found a better collaborator in @dan and the documentation for the problem is already sent off to engineering!

Even the circles that have cut out don’t look very round to me, including the outside. They all use the SVG circle primitive, so should be perfect circles rather than polygons.

Yep, this was great!

I’m honestly not sure how perfect things are supposed to be.

I put the sample cut on my flatbed scanner to get a good top-down image. This is the worst-looking 3 mm circle, with an Illustrator circle overlaid to help highlight irregularities. There is definitely a bump at 5 o’clock. The whole cut is only 3 mm across though, so the defect is pretty small. I assume this is reasonable variation for this kind of machine.

Then again, most of the other small circles do look better, though each has a notch at 3 o’ clock, where the cut starts and ends. (This is more obvious on some materials like acrylic.)

Here’s a big picture of the whole piece, with an exterior circle overlay. It looks pretty round to me in this view, though the 3 o’ clock start/stop notch is still there. The poorly-cut circles have really obvious aberration though.

Anyway, I look forward to this bug being silently fixed in a future surprise update, heh. :wink:


I reported this behavior on Jan 10 under the title Inconsistent Cuts. It was resolved as “Working as intended”

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No CNC machines can normally make circles that look perfect to the eye, even when fed with polygons. In this case the SVG specifies a circle.

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Perhaps they will take another look.