We had a job recently to install plexiglas shields over a forged steel gate/railing to keep people from reaching through the ballisters and unlocking the gate. We'd have to drill many holes in 3'8" thick plexiglas, on-site, to mount the several pieces that had been professionally precut to various shapes. Not a good place to fail. Having had some bad previous experiences cracking the plexiglas when the drill breaks through, I convinced the boss to stop by a glass shop on the way to the job and ask them how to prevent problems.
S000000000 simple! When I asked the guy, and used the word "drill", he said no no no. Juat take the size drill you need, heat the SHANK end with a propane torch and push that end through. As the drill melts its way through, it leaves a little hump of melted and resolidified material at the edge of the hole. Just take a razor blade and carve it off.
Pracitce one or two holes first, to get the feel of the drill bit wanting to slide as it makes the puddle.
---Works GREAT!!! ---Every time!!!