Check these guys out, they did a great job! http://www.customlasercutting.com/ Instead of machining polycarbonate at a pretty dicey price, I can get great quality plexyglass parts for way less. No word yet on the tolerance — I’m going to measure a statically significant number of these little windows to see if I need to move the nominal laser path. Also, they have a pretty bad thickness tolerance of +/-10% (nominal 3mm). So far I haven’t been able to track down a better material that has the other properties I want, but I know you can get +/- .005in. Oh, and despite the picture (where I was playing with direct reflection thanks to my photography book) this stuff is tinted which I like. The pieces in the pile all have the protective backing still on them.