I've often written about getting acrylic parts cut at Metrix, the local hacker space. It's awesome to have a panel cut where, if you've measured carefully and made an accurate drawing, the holes are the right size and shape (like D-holes for switches and pots) and everything lines up. You may be thinking "That's great for you, but what about me? There's not a hacker space anywhere near me."
I made a discovery. Many trophy shops have lasers these days to make plaques for trophies and awards. In fact, engraving is one of the things they do all the time, so they may do a better job than a hacker space! The trophy shop about 2 miles from my house did a superb job for me when I wanted better quality engraving than I got at the hacker space, and it was cheaper too. They were happy to work with the file I supplied to cut and engrave my panel.
There is a rule for the clearance of screw holes: 10% bigger. So, a hole for an M3 screw should be 3.3mm, for an M6, 6.6mm, etc. For laser cutting this isn't a problem, but if you have to drill, is not practical. So, I use D+0.25mm for M2,M3 and M4, D+0.5mm for M5, M6 and M8, and D+1mm from M10 uppwards. This is aplicable to all round holes, not only for screws. See a chart.. If you want a thigter fiting, use D+0.25 for all.
For other shapes, is better to forget ISO tolerance tables, since you only need a loose fitting. Just use dimension+0.25mm for small shapes, like slide switches, and dimensinon +0.5mm for bigger shapes. If you are confident with your measurements and the precision of the cuts, just use dimension +0.25mm for all.
Also, you must know if the cut is made over the center of the line you drawn, or if it's compensated to the inside for the laser width. If the cut is over the line, you will have a bigger cut, and you must compensate in the drawing (just an offset to the inside of the shape of half the cut widht.)
I'm a mould designer by trade, and used to work with much, much thigter tolerances. If you need a tighter fit, just ask. (Whithin the capabilities of the laser machine and your measurement tools)
I tried engraving award plaques and trophies several times in the past. But never got a satisfactory result. Last week I went to a shop named Hoult-Hellewell in Scarborough to engrave in one of those plaques. They use laser engraving technique. They did a great job with the perfection I will never make, if I try it myself unless I own a laser engraving machine.