I picked up a few small sheets of cast acrylic to see how it would turn out. I used an O Flute 1/8” bit to carve this text. This could be the result of a whole bunch of problems, but has anyone ever cut acrylic to where it’s perfectly smooth and doesn’t have the bit spirals? The sheet was 1/8” thick and as flat as can be.
How did you workhold the part? You might need to use double sided tape or the blue painters tape + CA glue method to keep the thin plastic from lifting as it is cut, that is what I’d suspect happened. I’ve never gotten it perfectly clean but it usually can be polished up with some heat or solvents.
In the past I’ve used acrylic adhesive to polish plexiglass. The glue was water thin and applied with a squeeze bottle with a needle applicator. The glue melts the acrylic and smooths it out. I believe it was done with methylene chloride. Look up vapor polishing. It’s been a very long time but I would try putting just enough glue in the cut to fill the bottom completely. If it works it’ll be much easier than flame polishing.
How deep did you cut into the plexiglass? You could try a second pass taking a very thin pass and adjust the speed to see if fast or slow works better to get it close.