# Cold Fabricating Lexan... how do you do it?



## 33706 (Mar 5, 2008)

Polycarbonates are great for making things. Lexan, a GE product, was specifically created for bend-ability in a good sheet metal brake. I've made lots of brackets, hangers and fixtures, it sure solves a lot of problems. However, I've never had much success with forming Lexan with the use of heat guns. Seems like any unevenness in the application of heat usually results in tiny stress fractures which affect the transparency of the material. Anyway, I want to make some cabinet doors with a gentle bow to them, rather than plain flat doors. I want to use 1/4" or 3/16", which, I expect, is far too rigid to follow the cope of the door frame stiles. Should I make some sort of English Wheel thing, like for sheet metal?? This is for a bow-front china closet; I've already abandoned the idea of using glass even if I COULD find something available. You-tube doesn't seem to have what I need for reference, mostly cold bending, or heat-gun forming. I want distortion-free curved panels. What do you suggest?


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## racerglen (Oct 15, 2010)

I'm not sure about the actual arc's possible or how sharp a bend you want but there's a 
(as always !) higher priced spread..
I think the brand name is "Mar Guard" or something like it. It's a higher grade of the Lexan stuff I guess, thicker and tougher, (Bullet proof glass ?? ).I've seen it used as a windshield in a late '50's Corvette roadster drag car, and if you look at those windshields the turn/curve to the post at the edges is quite severe..this one had been in use for 4 years at the time and only very slight stress fractures had resulted at the very top, sharpest corners in an 8 second drag car..
The guys say it takes a great bend, without distortion..I'd never have known it wasn't glass if I hadn't been told..
(and unlike Lexan, it wasn't all scratched up !)

Rambles from the Okanagan..


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## bigike (May 25, 2009)

bentlyj is right this is the way we do it at work every day one kid there is real good with that stuff me i can only take out scratches and stuff like that. pre heat the oven and if you can make the piece over size and get a sheet of rubber thick heavy rubber for the form use laminate like from a counter top and mdf put the form in the oven with the lex on it then in about a few hours take it out place the rubber on it with a reverse form on top of that and clamp it when it come out trim to size and you should be good to go. make shure everything is clean though no dust what so ever.


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## crank49 (Apr 7, 2010)

Blow or Vacuum molding also work; airplane canopies are vacuum formed. But with any forming process, the main thing is long and slow even temperature. You can build a box, insulate it, heat it indirectly with a few heat lamps (avoid direct IR on the plastic), but it takes hours.


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## 33706 (Mar 5, 2008)

Thanks for all the great replies! I'm going to scrounge up some old, smoke-tinted stuff I've hung on to forever, I may as well practice on something I don't really need, rather than wreck a piece of store-bought stuff. I'll think of a 3-roller design, and see what springs off the drawing board*! Glen*: I'll try to source out some 'mar-guard' here in Canada. Sounds interesting! *bentlyj*, I think you may be on the right track. I googled "slip rolls" and though there were no specific sheet metal rigs that specifically said they do lexan… I'd bet they do! I was surprised to see some of our favorite woodworking brand names affixed to sheet metal tools; like Fein and Jet. Wonder if there's a site named *"Sheetmetaljocks"* where metal workers endlessly debate the merits of their favorite machines. Of course there would also be a few classic examples that swear by "Central Machinery" sheet metal tools and crap by HF….ya think?


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## GaryK (Jun 25, 2007)

Using a slip roller would be a good first start.

Find a local sheet metal or auto body shop and see if they will let you try it out.


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## Gene01 (Jan 5, 2009)

There's a bunch of info here Bending Lexan


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## Tearen (Aug 2, 2007)

We do a lot of Lexan forming for fixtures and assembly aids. We make a 2 piece forms. We place the lexan on the bottom form and then we place the sandwich into a 80C oven. As the Lexan begins to bend, we add the top form and small weights. Once to the desired shape, we pull the sandwich w/weights out of the oven and allow the sandwich to cool for 4-6 hours. Trim to final shape.


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## Pimzedd (Jan 22, 2007)

I taught Plastics Manufacturing for 34 years. Let me pass on what I know about polycarbonate.

It will cold form. What radius are you trying to match? The thinner the plastic, the easier. Standard polycarbonate will scratch fairly easily since it is a soft plastic. Racerglenn talked about some that is scratch resistant. I had some one time. Did not scratch easily. Don't remember the manufacturer. Another plastic that will cold form is PETG, the plastic that soft drink bottles are made of. It will form easier than PC. PETG will also scratch.

PC can be heart formed. To form it, it must be dried for 24 hours since it absorbs moisture. If it is not dried, it will end up with thousands of little bubbles (water turns to steam). Put it in an oven at about 180 degrees F to dry it. To form it, it must be HOT. It forms at around 550 degrees F.

A form can be made to shape it while hot. For a gentle curve, I would cut several pieces of 3/4 plywood with the shape of the curve. Mount them in a row parallel to each other. Cover with 1/8 in. masonite. Cover that with common felt like teachers use on bulletin boards. Heat the plastic in the oven. Lay it on a piece of cardboard while heating (the cardboard will scorch but not burn, dark brown is OK, black needs to be replaced). While wearing gloves, lay the hot (soft and wiggly) PC on the fixture and cover with another piece of felt. Pull the felt tight to hold the plastic down. Make the plastic over size and trim to fit. Finally, the final piece will probably have a small amount of spring back and not match the curve exactly.

If I were doing this, I would substitute acrylic for the polycarbonate. More scratch resistant, does not need to be dried, will form at about 375 degrees F.

They both will smell and if your wife is like mine, she'll know when she gets home.

Good luck.


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## racerglen (Oct 15, 2010)

Sigh..
Bill , LOML was very much aware that I'd been drying some green wood in the microwave !

;-(


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## Pimzedd (Jan 22, 2007)

Glen, after a while, playing dumb (what smell honey, I don't smell anything) just doesn't work any more. They always know dont' they.


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## 33706 (Mar 5, 2008)

*Bill & Glen:* Thanks for great replies! Which brings us back to my original query about COLD fabricating! I've been busted too many times for doing stuff with kitchen appliances for doing things they weren't designed to do. Heck, my LOML even found her missing three steak knives in one of my rollaways…..but, but, it was clearly labeled the "Knife" drawer!!! I once got busted for trying to powder coat a small bracket in a toaster oven…everything tasted horrible in it afterwards!


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## racerglen (Oct 15, 2010)

P\K the microwave in question's long gone to that great landfill on the hill..but the smell lingers on..
Bill, I'm reminded of the song stuck in the middle with you.. paraphrasing (nobody said I could spell..;-( .."husbands to the right of you, wives to the left of you. stuck in the middle with you…)
I wonder what an actual L/J in the flesh convention'd be like.. probably make Las Vegas cringe..


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## 33706 (Mar 5, 2008)

glen: for an instant sampling of photos of what LJ's would look like, you need only go to this site…but then you might have to take that *Great Mental Shampoo* afterwards: click here: http://www.peopleofwalmart.com/?page_id=9798


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## racerglen (Oct 15, 2010)

Oye Vey..
You had to do that didn't you !
One of my "friends " keeps sending me that series..
;-(


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## Pimzedd (Jan 22, 2007)

P/K - Did you have to post that? Had to look, wish I hadn't, glad lunch is at least two hours away. :-(


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