Yeah, lasers get dirty pretty quick when vaporizing wood 
This is what I found about a year ago after 3,000 wooden tokens engraved both sides…
So I also had the exhaust fan grill face-load and almost completely restrict airflow, and pump smoke out of every crack. Ok, that thing is in the way, causing the fan to blow directly into an obstruction. Not anymore.
Increased airflow, improving cooling with less turbulence - less smudge deposit on the fan. 