Plexiglass/Lexan Shaving/Shaping

Justin · March 24, 2009, 01:33:06 PM

Does anyone have any experience with shaping plexiglass or lexan before? I want to round the top of my windshield a bit and was wondering how challenging it would be. As well as what tools are involved, I was thinking it could be done with a belt sander and fine grit paper but i'm just speculating.

lragan · March 24, 2009, 02:03:28 PM

The thing you need to guard against in any machine grinding (belt sander, etc.) on these plastics is heat build-up. If the plastic gets too warm it starts to soften, clogging your tools (sandpaper, whatever you are grinding with), and very shortly thereafter, turning a dark color, which is the plastic oxidizing. I suppose if one persisted you might get a blaze going,

although I have never seen this happen.

If I were to try to change the shape of my windshield, I would

1) Dig out my old windshield that I scrapped because of crazing to practice on
2) Cover the area to be shaped with masking tape extending well into the area to be preserved (enough to rest the saw on , see 4 below)
3) Mark where I wanted it to wind up.
4) Cut it with a fine tooth saw at low speed (like a saber saw or such) on the outside of the line I had marked.
5) Grind/polish it the rest of the way by hand, using increasingly finer grits to get to a surface finish that I was pleased with.
6) Remove the tape and clean it up.

If all this worked, then I would work on the "real" windshield

Justin · March 24, 2009, 02:12:08 PM

Thanks, that's what i was kinda thinking. Other that i don't have another windshield to practice on. But i'm really just knocking off the edges of the window to take it from a rounded square to like an ovalish shape.

Ultimately I want to shape the window and then put a Limo tint on it so when I connect up the LED lights to it I made the light wont filter back into my vision and will just be reflected forward.

Thanks again for the advice, I thought about using a wet sander too with running water to dissipate the heat to prevent the build up on the belt, but i'm not sure if they make wet sandpaper in belt form, i guess i could check and automotive or boat shop.

roboto65 · March 24, 2009, 02:18:47 PM

Curtis is the expert on this he will chime in soon and it does involve chemicals LOL

Curtis_Valk · March 24, 2009, 08:11:59 PM

I posted a link to one of our past discussions on the "other" windshield thread.

Lawrence has it right though. I use a band saw just because I have one. If I didn't I'd make do with a saber saw. To get the factory looking finish though after cutting and just light sanding to hide any crooked cuts I wipe the edge with MEK. It chemically melts the lexan, so you MUST NOT get it on any part of the shield but the very edge. To accomplish this a helper is good to have. The windshield must be held with the edge you are wiping DOWN so gravity will work with you and not against you. Any MEK that runs will RUIN your windshield.

Curtis

lragan · March 24, 2009, 09:06:18 PM

Use in a well ventilated area, and hold the work downwind. Methyl-Ethyl-Ketone (MEK) use in the electronics industry was severely restricted (along with Trichloroethylene) in the early 70's. A little exposure will probably not harm you, but caution is advised.

http://www.scorecard.org/chemical-profiles/summary.tcl?edf_substance_id=78-93-3#hazards

Curtis_Valk · March 24, 2009, 09:12:46 PM

Thanks Lawrence for adding that. Yes, MEK is bad stuff and exposure needs to be limited or avoided altogether (before you use rubber gloves, make sure the MEK won't eat them).

Curtis

Smoked U · March 25, 2009, 10:49:12 AM

Fabricators also "flame" the edge of lexan/polycarbonate with a heat source to cause a slight melting effect that will clear the edge up once it has been sanded fairly smooth. This of course requires a good heat gun or a small torch, a watchful eye and a steady hand.

Justin · March 25, 2009, 02:24:19 PM

Thanks for all the info guy's, I just happen to have MEK at home already for use with Electronics so it should work out well. Would you say that MEK would probably produce a better finish then Heat??

hootmon · March 25, 2009, 02:55:48 PM

I would think that the MEK would be easier to control.. IMHO

Curtis_Valk · March 25, 2009, 03:25:52 PM

Quote from: Justin on March 25, 2009, 02:24:19 PM
Thanks for all the info guy's, I just happen to have MEK at home already for use with Electronics so it should work out well. Would you say that MEK would probably produce a better finish then Heat??

One more caution on the MEK. If you wipe it and don't quite get the desired edge finish let the MEK evaporate completely and let the lexan return to its hardened state before you wipe it again or it will start to smear.

Curtis