Steaky engraving "woodgrain"-like texture on engraved plastic

[Pete Bejmuk]

Our Epilog Legend32 is having problems engraving. When engraving plastic, the engraving looks like raised woodgrain – it’s not a smooth engraving anymore. Our other lasers are engraving fine and smooth. These “wood-grain”-like streaks do not appear when engraving the same material with our other lasers – it’s smooth and clear.
This is most pronounced when engraving reverse romark, or paint-filling extruded acrylic from behind - the "woodgrain" streaks appear white, even after cleaning.
Epilog suggested the following, which I checked: Optics are clean, alignment is good, focus is good, Settings are the same as before
I also noticed that there is a LOT more smoke residue when engraving on the problematic machine, compared to before.
Any suggestions?

[Joe Pelonio]

I have found that extruded always leaves a streaky white appearance, and use only cast for paint filling.

I have not had that problem with reverse Rowmark. I wonder if by chance they sent you rotary material by mistake?
Try doing large square on a scrap of regular Rowmark, and see if it comes out nice and smooth. If it does it's probably not the laser. If it is streaky, then try moving the head left, right, up and down with the machine off and see if you can feel any free play or roughness in the way it moves. There could be excessive wear, or maybe a lack of grease causing the Y movement to be less smooth. Usually, though, it's a beam issue. When you cleaned the mirrors, did you see any missing gold or scratches?

[Scott Shepherd]

I have seen that in the past. In the cases I have seen, it has always been optics based. Either there is a dirty/faulty mirror or lens in the line somewhere, or the focus is wrong. You said the focus was okay. How did you check the focus? With the gauge? If so, I'd do a manual focus check and make sure your gauge isn't off. Setup a piece and vector mark lines, then bump it down in focus one click. Do it again. Keep doing that until the line is the thinnest, move it back to that spot and rest your focus tool.

That's my guess. I'd certainly try moving the Z around, up and down, and see if you can find that sweet spot and I believe this might solve your problem. Check it and report back!

[Chuck Stone]

I don't have the experience these others do, but your description doesn't sound
like optics to me. Sounds more like vapors settling back onto the material. That
would lead me to air flow.

[Delbert Rippetoe]

I have a new epilog and I now have to make sure it is a tad out of focus to get good results. I auto focus against the table (without plastic) and then engrave with auto focus off and get excellent results.