Inconsistent amount of flashback

I just ran a job on teal PG acrylic, no different than probably 85% of my jobs. Crumb tray was clean, masking was on the PG and I used the default PG cut settings for teal, and these were all cut from the same general area of the sheet. Of the 6 pieces cut, 1 had a crazy amount of flashback. The rest were (relatively) fine. Not only did it visibly mar the acrylic, but you can feel it too. All of these were laid out perpendicular to the supports within the crumb tray. I’ve been seeing more worse-than-average flashback lately, but nothing this bad.

Thoughts on what may be causing the inconsistency? Seems weird to me.

Was that piece closest to an edge? (Sometimes the air feeding in under an edge will just toast the cut on the bottom.)

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No closer to an air source than the others. And the one that’s the worst is towards the center of the sheet and was cut as #5 of 6. (or, 7 as it appears here since I had to cut an extra to make up for the one that got fairly charred)


Could be a flatness thing, so you have more or less energy available? Or a little bit of curvature in the crumb tray?

Had a curious thought (probably too much coffee).
If the actual cut was aligned with a crumb tray track for the entire run and therefore always at the end of the beam (instead of track, gap, track, gap) could it make a difference? If so, the constant flashback would be a very random event and hard to analyze.

You mentioned they were perpendicular to the track, but the thought flowed anyway.

Got my eyebrows together, so I guess it will have to be tested now…


Did the flashback appear to lessen as the print progressed with the most at the beginning or at the end? That’s way more than should be happening in any case.

I’m not sure where on the cut it started & stopped, so I couldn’t say. But I agree that it’s definitely more than usual. And the fact that it was just one piece out of a total of 7, using PG settings on PG, flat on a clean bed. There’s no reason that one individual piece should have it like that but not the others. So odd.

This feels like the right track.

That would be my thought too, but those run front to back and what you’re seeing in the pic was oriented side to side.

Just curious…Was the shape aligned parallel to the Y axis (north to south) , or parallel to the X axis for the cut?

There are metal supports that run North to South inside the crumb tray. If it just happened that the item you were cutting fell right over the top of one of those on the tray, the beam would reflect back onto the backside a whole lot hotter at that spot, and might cause that flashback.

Parallel to X. Hence the mystery.

Chuckle! This is triggering the Sherlock in me. :smile:

Is it possible the masking wasn’t securely attached at that spot? Little loose, or a fold or bubble, or thin adhesive?

There was nothing visibly odd there. This adhesive is a possibility, but it’s so close to other areas that cut normally that it seems unlikely.

I’ve run a few jobs since this one and haven’t seen it happen again. But even before this it was sporadic. I’ll have to start watching for some sort of pattern.

I’m sorry your print didn’t turn out beautifully! I took a look at the information from this print, and I can see there are two identical layers included in the second design from the bottom. This results in an additional pass over the same cutline, and more flashback as a result.

Could you please try the following?

  1. Open the file in a design software program such as Inkscape
  2. Select the design, right-click, and choose “Ungroup” three times
  3. Using the selection tool, choose the second design from the bottom
  4. Right click that design, and choose “Delete”. You should still see one layer
  5. Save the design as a Plain SVG
  6. Upload the file and print!

Please let me know if this helps. Thanks for letting us know about this!


Whew! I love an easy operator error! :slight_smile: Thanks!

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