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I need to cut kind of thick plastic

I have these "universal" plastic speaker adapters:

http://www.crutchfield.com/App/Product/Item/Main.aspx?g=103200&i=142SA69&tp=919

But the hole in my car is too small to mount the speaker on top, and the hole in the plastic is just slightly too small to fit the surround of the speaker if I mount it from the bottom. I figure it will be a lot easier to widen the hole in the plastic rather than in the car's sheet metal, but it's still not easy. Any tips? I've tried a box cutter knife, pocket knife, soldering iron, torch with soldering iron attachment, chisel, etc. Probably gave myself cancer from the fumes from trying to melt it. It's not terribly tough plastic, but it's kind of thick, so it's not easy. Plus it's difficult to cut a circle from the inside. I need to increase it from 13 cm diameter to 13.5 cm.

h142sa69-f.jpeg
31 comments
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Jul 26, 2008. 9:37 PMWeissensteinburg says:
Too bad about the dremel, but at least the speakers are working!
Jul 27, 2008. 10:42 AMWeissensteinburg says:
Where does it go?
Aug 16, 2008. 5:24 PMgimmelotsarobots says:
Ooooh. You shouldn't have torn it apart. That would have been covered under warranty. Mine Broke and I sent it in. A few weeks later I got a new one in the mail! If you had it less than 5 years it's under warranty. But you opened it and the warranty is voided. Although, I like to fix things. Good luck with the repairs! not sarcasm
Aug 17, 2008. 2:51 PMgimmelotsarobots says:
Cool! I'll always take the easy way out if I can because I usually have many projects going at once so any spare time I can get is much appreciated.
Jul 27, 2008. 1:25 PMWeissensteinburg says:
Will it be easy to replace?
Jul 27, 2008. 4:46 PMWeissensteinburg says:
You can't get it from the link you posted above?
Jul 27, 2008. 5:17 PMWeissensteinburg says:
Gotcha...maybe you could call Dremel and get it cheaper, though.
Aug 14, 2008. 6:28 PMWeissensteinburg says:
Awesome, good luck with the repair.
Aug 15, 2008. 11:57 PMclasic_traveller_diehard says:
did you try tin snips?
Aug 15, 2008. 6:50 AMFlumpkins says:
How bout' a chainsaw?
Jul 26, 2008. 10:30 AMWeissensteinburg says:
Since the dremel has already been suggested...sand paper? If the math the forge did is correct, a tenth of an inch isn't much to sand off.
Jul 25, 2008. 9:31 PMforgesmith says:
Sure hope you got them for free, only 1 of 7 reviewers didn't report modifications, with one of those simply using them for a template.

You don't have to cut it, just shave off some from the hole. A half-round file with the part in a small bench vise would work, file close to the jaws to keep it from vibrating much. Likewise a Dremel with a straight cylindrical burr would work nice. Don't know about using any kind of grinding or sanding tool with the Dremel as the plastic would likely clog them up pretty quick.
Jul 25, 2008. 10:26 PMRishnai says:
Sawzall, portable jigsaw, or scroll saw is what you need. You could also try to file like forgesmith suggests, or use a sanding drum. The sanding drum on your dremel would work, if a little slowly. A three-inch drum the you can check into your drill is probably better, and would be handy to have around anyway.
Jul 26, 2008. 12:28 AMforgesmith says:
Math is an issue. 0.5 cm diameter increase => .25 cm off the side => just under a tenth of an inch to come off, about 3/32". How thick and wide are the blades for your sawzall (reciprocating saw)? That'd be a tricky cut with anything but the scroll saw.

Does the entire circle need to be increased to get the speaker in, or just some high spots taken down?
Jul 26, 2008. 12:50 AMRishnai says:
I've gotten some pretty precise cuts with some clamps, a vice, and a jigsaw. It's less like removing a chunk than making a chainsaw carving, where you're using the saw and blade in the non-reccommended manner. I've done a little plunge-routing with a battery drill and creative clamping, too, but I wouldn't want to have tried either for the first time on anything that wasn't free...
Jul 29, 2008. 12:11 AMRishnai says:
Excellent idea. That would give good control and good cutting.
Jul 25, 2008. 8:36 PMSenseless says:
Use a handheld router like for use on drywall, and a drywall blade that's got the threads opposite of a cutting blade for wood and go slow. It will melt you a nice line. A dremel might be able to do it to.

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