I'm trying to cut 1/32" and 1/16" birch plywood consistently with a 25W ULS 25ER laser cutter. On some sheets, it cuts like a dream but on many it won't cut all the way through. I realize that there is often denser wood in spots which is probably causing some of my problems.
Here is what I do to cut it. First, I focus at the surface then crank the lens down 1/4 turn for 1/32" ply and 1/2 turn for 1/16 ply. I cut at speeds at 1.6 and 1.2% full power and 350 to 400 PPI. I raise the material 1/8" off the engraving bed using 1/8" square brass tubes. To keep it from flaming, I dampen both sides of the wood.
This will work mostly for about 5 minutes but after that the airflow dries out the surface and flaming occurs. I then pause and with a wet paper towel, I dampen the surface and begin again praying that I haven't moved the wood.
In some of my sheets it can take 15 minutes to cut. The massively frustrating thing is that sometimes the wood takes up a lot of water and becomes soggy and the laser won't cut through. OR it won't take the water at all and it flames and when it flames, the laser won't cut through.
On dry warm days, with low humidity ( common here in California) the wood can be almost dry in 5 minutes. I try not to wet the bottom of the sheets too much because all I need there is to keep it from excessive burning but too much just saps away heat.
I always start with a clean lens too.
I can't drop down to 0.4% speed because the laser won't fire that slow.
I know about the waterproof glue that they use in this plywood and how it acts like a mirror to the laser beam. I wear sunglasses when cutting this stuff as a precaution. I heard that there is birch plywood made from a laser friendly glue but I cannot find a source. Does anyone know of one?
It is really maddening to flip over a sheet and find that it hasn't burned though. My only recourse is to cut the rest with an exacto knife and that looks terrible. The customer paid for laser cutting not laser marking and hand cutting.
Is there something I am missing here? Does anyone have a trick that makes this stuff cut reliably or is it simply a matter of more power? Or is this a job for an air assisted laser cutting machine?
Kay