I picked up a couple of sheets of clear plasti card for windscreens, but the old CD case trick is one to remember
When cutting brittle plastics, try using one of these, easy to make out of scrap wood. Or get a kit like this for the fine tooth saw. For those that don't know, the workpiece sits on top of the wooden frame, have the saw cut as close to the wood support as possible, and the saw teeth set to cut downwards. Same principal as using a fret saw
Set of Jewelers Bench Pin & Clamp With Ring Cutting Jig+ Saw Frame & 12 Blades | eBay
https://www.ebay.co.uk/i/252422056204?c ... 69fffa222a