I have a pile of different colors around, it's useful to me as I'm slowly adopting a swimming pool mentality - make plates that can hold different combinations of pickups, and move them around.
Hacksaws are OK, but if you load them with a tugsten carbide blade they'll cruise through any plastic or wood. Sandvik makes a great one, I bought a case* of "BAHCO 3816-300" not long ago that kick pootie. Hey! They're British! Don't pay $10 for one, there are some seriously silly sellers... half that, maybe. There's some RemGrit ones on (US :sad1
Ebay, 3 for $7.50, that's more like it. These also cut of both forward and backward strokes, everybody KNOWS that regular hacksaw blades are destroyed by breaking off their teeth going backward - right? (FILES TOO!)
Wide blades only cut straight lines, so you have to figure out how close you can get inside each inside curve with a combination of straight cuts. A 'map' even. Depending on your vise/clamping arrangements, you may need to support the plastic along the side of the cut by clamping it between some scrap wood. The saw cuts so quickly that the time spent moving the bracing takes longer than the cutting!
The hard part of it is, it cuts so easy a little too much enthusiasm can be ruinous. (For pickguards
only, it might be worth it to keep one of the tungsten carbide wire-all-around "rod" hacksaw blades, they break if you bear down on them on hard stuff but pickguards ain't.)
Wood rasps do OK on the finer stuff, but the evilest 50-grit wet/dry sand paper is my favorite - FAST - wrapped around something sturdy you can probably take off 1/4" with five really bearing-down strokes, and you can wrap it around whatever shaped thingie you need.
Any sort of speedy power sander is highly likely to melt the plastic and gum up permanently. Dremels + plastic will destroy just about any tip you stick in there... I've never managed to do that hand-sanding, but these carbide saw blades WILL gunk up instantly if they cross through... masking tape! And masking tape is important. A little brass brush or file brush is easiest to clean them off, any sort of Goo Gone or just vegetable oil will dissolve it messily but the brushes are fast. EVERYbody already KNOWS you always brush off your saws and (especially) files when you're done for the day, right? The dust and gunk traps the moisture, and moisture makes rust.
*(Files too, I HATE working 2wice as hard bearing down on some crapped-out old file... I was buying a doublecut coarse bastard file at least every two years, at whatever price I'd pay when I was mad enough at my fracked old one.... files are DISPOSABLE. They're like TOILET PAPER, you don't SAVE them.
I don't. Tools like that are about 1/2 price in bulk.)
http://en.wikipedia.org/wiki/File_%28tool%29