Especially for drilling Plexiglass you need to grind a bit so it can't grab I.E. backwards or neutral cutting edge. Lexan not quite so grabby. Drill for good clearance with fastener.
I have drilled a lot of acrylic... I have found brad point wood drill bits work best for me. I don't think I have ever cracked acrylic with brad point bits even when drilling close to the edge unlike chisel point bits,