Ï had great results with plastic board and/or perspex with one-flute 3.2 mm bit at low RPM and perfectly clean cut...
1/8"(.1250") single flute carbide endmills for plastic | eBay
I'm trying to cut some 3/8" plastic cutting board (Building a 24" x 48" machine) but my bit keeps melting the material ruining the piece every time... I'm currently using a 1.8mm end mill. It seems to go longer without clogging at slower spindle speeds but it still clogs eventually... Maybe a larger bit?
What rpm did you cut at I can go as low as 5000 rpm!