I'll speak to the grades of ply. DO NOT by underlayment from ANY of the big box stores. It has very hard and a LOT of glue that is probably an epoxy based. I can cut great and then hit a spot and laser won't even dent it at power needed to cut thru the clean areas. I've found my local HD to have decent Baltic Birch (marked as such) at 3 and 5mm thickness that is flat and easy to cut. Three layers. Thick center ply and two thin veneers. Not 5 layers, nor 3 that are roughly same thickness. Look for thick center and thin surface veneers. Those will cut well and Yes, double to triple the cheap ply costs...... But well worth it.
And Half inch MDF is impossible with my 80watt. Charred Mess. I have a bunch of 6"x96" pieces I create as scrap from my other projects and it just sits. Guess I could engrave rather than cut couldn't I? Anyone have project that uses 6" x MDF in half inch? Just ends up as jigs when I can use it.
Woodworking, Old Tools and Shooting
Ray Fine RF-1390 Laser Ray Fine 20watt Fiber Laser
SFX 50 Watt Fiber Laser
PM2000, Delta BS, Delta sander, Powermatic 50 jointer,
Powermatic 100-12 planer, Rockwell 15-126 radial drill press
Rockwell 46-450 lathe, and 2 Walker Turner RA1100 radial saws
Jet JWS18, bandsaw Carbide Create CNC, RIA 22TCM 1911s and others