You should make a video of a hole saw drilling clean, crack free holes into thin polystyrene.
No video but here is the third attempt of using 1" hole saw (with a pilot bit) in 1mm polystyrene. The first two cracked simply making a pilot hole with a small standard bit preparing for the hole saw. I was using a hand drill, 500rpm, not clamped, held down on a piece of wood. Results would be better clamped, I would assume.
The small hole in the picture is using a step bit, the large hole using a 1" hole saw. Both a bit rough but easily smoothed with sandpaper.
I've had 1mm polystyrene easily crack using a step bit as well.
So my conclusion is to have BOTH a step bit and hole saw available, clamp well and use minimum pressure while drilling.
