I'm kinda surprised the 1/4 inch plywood is stiff enough to work without something under it (like a workbench). Those garbage cans must give it a lot of support.

Are you cutting with the rotary cutter moving at right angles to the grain on the face of the plywood?

I don't use expensive baltic birch. I use the cheapest Lauan. I've found that when I make repetitive cuts in the same direction as the grain I eventually cut free long thin slivers of the wood. These aren't a problem as long as I catch them before they stick me. Cutting across the grain minimizes these. I wonder if the thin face veneer on the lauan is more likely to splinter.

PGJ