Too much flashback!

I am cutting Baltic Birch plywood, and I have been cutting BB for a long time. I have two machines, and one of them cuts just fine at 165/full, but the other one burns the back of the plywood and flares up quite a bit (small flames inside the GF).

Here are examples of the backs of the same material, the same file, but one was done this summer, and one was done last week. Same settings, same wood.

What could be the problem? It seems unsafe at this point with the amount of flames. Is my laser getting old or the fan system?

Same type of printer or different?

It could be caused by the moisture content of the wood. More moisture would require more power to do the same thing. If the left pic is the last one you did try lowering the power or increasing the speed until it just burns cleanly through.

Are you totally certain both machines have their lenses installed right side up?

Do the tops of the two prints look the same?

The muckier the crumb tray the muckier the flashback.
But what you’ve got going on there looks very different

I’m sorry for the ongoing trouble with your unit. I see that you have an email ticket open with us as well, and I’ve sent you some information and next steps there, so I’m going to close this thread and we’ll continue to assist you via email.