POT: Acrylic Bending Jig

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Possibly OT. Excuse the x-posting, but there doesn't seem to be one group for this stuff.
I want to bend some Acrylic, so I plan to build a jig. (Too much free time) The plan is to use a couple of knife hinges to separate (1") two pieces of particle board (insulated). I will place some NiChrome wire (2') between the two boards and heat it up with a 24V transformer and a light dimmer. Once the Plexi is warm enough, I'll move my hinge to the desire location and clamp it off.
Has anyone attempted something similar? Should I clamp the Plexi on both sides of the hinge when bending or do I need to allow one side to move, to prevent cracking?
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Forget the putting of the nichrome between boards(you wanna collect insurance?)
I'm going from memory, but I believe the book "This Old Boat' describes what you are doing. I don't remember it saying to clamp both edges, but I suspect that has more to do with the size of the piece than anything else. Take a look at the book, I have tried many things from it and all have worked, I don't see why that project would be any different.
--
MonteP
"Let bygones be bygones...send a concilliatory PRETZEL to the
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A simple, not-very-expensive option is to use heat tape which warms the plastic enough for the bend. Take a look at: http://www.usplastic.com/catalog/product.asp?catalog%5Fname=usplastic&category%5FnameY&product%5Fid#01
(If the link is broken, to to www.USPlastic.com and search on "Plastrip heater".)
Alex

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The heat tape is what I use. The one I have is 15 years old. It works really well. The trick is to use the right kind of plastic, and not too thick. 1/4 works very well. Jack

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Bending acrylic is fairly simple but toaster wire at 24V might not give you enough heat. At the plastics shop I worked at they hat a kluged strip heater like you describe but it had a cal rod heating element running at 220V about 3 or 4 inches from the plastic.
Try setting up some bricks about an inch apart and then take some foil and wrap it around the bricks so it will droop in the middle to make a reflector.
For the heater coil, take your ni-chrome and coil it around an 1/8 inch rod and when you have a coil tightly wrapped about 3/4 of the length of the piece you will be bending. Remove the core and stretch out the coil to length. You can try your transformer, but I suspect you might want to run this at 110V. It kind of depends on the size and of the wire and the length. If it glows white you have too much voltage, or too short of a length.
You might also want to dry out the plastic prior to forming. Acrylic absorbs moisture that will cause a rice crispies effect as the plastic softens. We had an oven where we would dry sheets overnight at about 150F with air circulation.
Good luck.
--

Roger Shoaf

About the time I had mastered getting the toothpaste back in the tube, then
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you might try contacting euclid, who make resistive elements for kilns.
http://www.euclids.com /
they can tell you how much you need at what gauge at what power to produce the heat that you need. they're very helpful if you give them a call and talk to them directly. they may also have what you need in stock.
regards, charlie cave creek, az

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if you go to your favorite thrift store and buy an old toaster, hair dryer, or electric grill, you'll get nice heating elements, properly sized, really cheap. Put them in series with a lamp dimmer so you can control temperature.
snip 00000000000

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Fri, Dec 3, 2004, 10:15am (EST-3) snipped-for-privacy@nowhere.com (william_b_noble) says: if you go to your favorite thrift store and buy an old toaster, hair dryer, or electric grill, you'll get nice heating elements, properly sized, really cheap. Put them in series with a lamp dimmer so you can control temperature.
Or maybe just put a big cardboard box over the whole project, or tent it, to keep the heat in. Be best to keep a close eye tho, to make sure you don't set it all on fire.
JOAT Be who you are and say what you feel, because those who mind dont matter, and those who matter dont mind. - Dr Seuss
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Also you might try your wife's hair dryer. You might have the super model designed for peeling paint. That would have lots of heat.
Dick

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Keywords:
<snip>

I bought a strip heater from a local plastics shop, and they had instructions on how to mount & hook it up. It was about 15 years ago, and I don't think I still have the info, but I've got the heater still mounted on a board with fiberglass felt insulation. Just plug it in, wait a bit & bend.
The heater is a flat flexible woven sort of thing, about 30" long. It probably doesn't draw more than a few hundred watts. It's mounted in a groove between two pieces of the felt covered in aluminum foil. No Variac required. It takes about 5-10 minutes to warm up enough to bend 1/8" plexy, but it's always worked nicely. I don't recall trying to bend anything heavier, but I think it will work up to 1/4" if you are patient.
Doug White
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IRRC the cal-rod heating elements are a nominal cost. That way you can get one rated for line voltage and avoid all of the experimenting.
--

Roger Shoaf

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Much safer:
http://www.usplastic.com/catalog/product.asp?catalog%5Fname=usplastic&category%5FnameY&product%5Fid#01

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Fri, Dec 3, 2004, 6:14am (EST+5) snipped-for-privacy@here.not.there (CheezWiz) put out: Much safer: http://www.usplastic.com/catalog/product.asp?catalog%5Fname=usplastic&category%5FnameY&product%5Fid#01
But pricey. I got a little ceramic heater, the type with a fan, and it oscillates, for about $19-20 at K-Mart. Screwed up and had it pointed at a telephone, about 16" away from it, and it on only half powr - softened the plastic enough to change its shape.
Or, if you want to go even cheaper, try borrowing your wife's hair blower, bet that'd work too.
JOAT Be who you are and say what you feel, because those who mind dont matter, and those who matter dont mind. - Dr Seuss
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(CheezWiz) put out:

http://www.usplastic.com/catalog/product.asp?catalog%5Fname=usplastic&category%5FnameY&product%5Fid#01
How'd you know I was a cheap bastard? :) Yes, I thought the $50 was a little spendy, but the big problem is that these guys use UPS. Since I'm north of the border, it would be more like $100 by the time they're done with their gouging. Besides, they're on strike up here now.

I considered the blow torch route, but the idea of standing there for half an hour breathing monomers or getting impatient and burning the plastic didn't turn me on.

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Bill Stock wrote:

I fear you won't get enough 'heat' that way.
I did a fluted ashtray 6" or so - and I warmed it in a small bench top kiln. The acrylic was rubbery long enough to get it into the bottom and top clamp.
Temp isn't the story - heat or calories is.
Martin
--
Martin Eastburn, Barbara Eastburn
@ home at Lion's Lair with our computer snipped-for-privacy@pacbell.net
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wrote:

Not quite like that, I clamped up some in the bench vice, then heated with a hot air gun, then bent it around some wooden forms. It worked reasonably well. It helps to have an assistant (SWMBO) and leather gloves for all.
Barry Lennox
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If its a pipe you're bending, you can fill it with sand before bending it, this will stop the pipe from getting kinks once bent.!

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Made many tables and plotting boards with bends using a heat gun, the oven in your kitchen works well too if the pieces will fit.
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I tried something similar without the transformer and " pop" off like a flash bulb. So I bought a 30" electric space heater ( looks like a baseboard type) and cut an opening in the back to allow me to slide the plexy through to the proper location. Worked like a charm. Cheers, JG
Bill Stock wrote:

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