I'd like to share an experience I had with flame polishing.

I was making some 5 sided boxes (4 sides and a top) from acrylic to be used as cake stands. I trim up the edges on a router table with a special plastic cutting bit. The bit leaves some very slight chatter marks on the edge. I found that if I went over the edges enough times with a torch, I could get the chatter marks to disappear (8 to 10 times with some cooling time inbetween). But when I glued up the boxes, I was getting micro cracks at the joints. Turns out the heat was putting stress into the acrylic, which was being released in the form of cracks when the cement was applied (the cement chemically melts the acrylic...more of a weld than a glue joint). I've even read that extreme temperatures can cause the cracks, but have seen no evidence of it.

Am I against flame polishing? Not at all. It is an industry accepted way of polishing acrylic. I am currently bidding on a job that will involve polishing the edges of pieces of etched acrylic. But I will be getting the edges as smooth as possible using varying grits of sandpaper (down to 1000 grit) before applying the torch. I've since stopped building the boxes, simply because the required sanding time to avoid the cracks made them unaffordable.

The moral of this story, if there is one, is to use as little heat as necessary to get the desired result, and if you have any deep scratches, work them out mechanically before reaching for the torch.

My 2 cents, if its worth that much.