Flashback Underside Burns on Birch Plywood


I recently place an order for a Glowforge Pro and I’m planning on using this machine to cut through 1/8" birch plywood for a product I plan to sell. I understand that this machine comes with a crumb tray but I’m curious how well it prevents flashback or underside burns.

I want there to be zero underside burns. Is it reasonable to expect this from this machine or should I look at an Epilog machine? Any advice wood be greatly appreciated.


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If you don’t use masking, there is a good chance you may get some flashback. You can search the forum for “flashback” and get some other ideas as well (I believe someone used aluminum foil on the tray?). But I would look at using a masking (lots of choices for that as well-some better - again, search forum for “masking”) Good luck in your venture - hope your :glowforge: arrives quickly!!


I think it’s reasonable to expect no flashback. Flashback can be an issue on any laser and I think preventing it has much to do with using the correct settings and masking than it does the specific honeycomb tray you use. I only use masking about half the time and I still don’t typically have a big issue with flashback. That being said, Epilogs seem like a good machines.


I use baltic birch plywood pretty exclusively and get very minor flashback about 50% of the time. Taking a few seconds to mask (or sand it, I suppose) would resolve the issue 100%. I could also probably run some tests and really dial in the settings - literally saw someone mention theirs on the forum, and stole them for my very own. They worked, never bothered to try anything else - but that probably tells you how minor any flashback I get is.

Honestly, it seems super weird to me that the deciding factor between a glowforge and epilog would be flashback. It feels like choosing a car based on the cup holders.


I get flashback sometimes on my BB, but I also don’t mask the back or put anything on my crumb tray to catch it. Either of those works just fine in my experience, I mostly just don’t bother. I just assemble with those bits facing in :slight_smile:

Also, FWIW, I find that I get the most flashback with cuts that have a lot of corners (no real surprise there) so that the head moves more slowly than usual and sometimes comes to a stop. In theory, software could eventually fix this issue.

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220/full/1x Pro. With masking, as little flashback as can be expected without taking additional measures.


especially true because you can get flashback on any laser cutter. i get it on the universal if the settings aren’t dialed in. and even then, sometimes i still see some. that’s why there’s masking.


I’ve never worried a lot about it unless it is excessive but as others have pointed out it is about settings and can happen in any laser.

Three things to minimize or eliminate:

  1. settings
  2. masking
  3. bed, if it is as important to you as it sounds, make or purchase a pin bed

I believe that the quality of ply you use also matters. Regular BB is B/BB face graded and include some defects in the inner plies. But the thickness of the plies allows for sanding. If you have intricate designs that wouldn’t stand up to the vibrations of the sanders I would mask, but if it’s simple shapes I think sanding is easier.

If you’re using birch ply with a better face plies they tend to be extremely thin and I would just mask them because sanding might go right through parts of the veneer. Unless you use pre finished ply which would be easier to clean with a quick wipe of alcohol.

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I have had a lot of success using baltic birch without getting any flashback by using power 100 instead of the max power setting. When using max power there are always burns on the underside and setting it to 100 it’s always clean.

Through trial and error, I’ve found settings for each material that I’ve used where there isn’t any flashback. It’s likely not the most optimal from a speed perspective and you will still have to clean the smoke residue off the top.


whats the thickness of your baltic birch?

I’ve had success with both 3mm and 6mm .

without changing speed? i thought a thicker/thinner one would be different speed/power settings. thanks for replying btw!

Obviously with different speeds and the number of passes in some cases. :smile: