I use a single flute endmills for cutting cast acrylic. I bought mine from drillman1 on eBay.
When I cut my pieces out, I used lead-in and lead-out paths (something you might try in addition to trying an offset cut). You can see these at the top of each poker chip in the second photo of the first post here: First Diamond Drag Project - Acrylic Commemorative Poker Chips