How are you cutting them at the moment? For our midline screws we use a jewellers fret saw and a really long smooth action. Sometimes for spring aligners we will use a tapered bur but the best one is a circular fret saw blade. It's teeth run the whole diameter of the blade so where ever and whatever angle you load the blade it cuts. Keep the strokes long and smooth and don't chop at it. A little wax on the blade will help it glide. Don't create to much friction as it will melt the acrylic and make the cut sloppy. Hope this helps,
- Patrick