POT: Acrylic Bending Jig

"Bill Stock" wrote in news:O snipped-for-privacy@rogers.com:

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.

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.

Much safer:

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

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

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.!

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.

Thanks Roger,

I've been looking for a detailed 'how to' for one of these gadgets, without too much luck. It seems most people use a car battery or a Variac for the power source. Neither of which I have laying around. The other big unknown is the wire guage/ohms as you indicated. I was considering 36 guage, but I suspect it won't generate enough heat. At least the wire is cheap enough for experimenting.

you might try contacting euclid, who make resistive elements for kilns.

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

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.

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Some data to help you calculate what you need:

-j

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

Thanks, very useful.

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

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.

Hi Bill,

I've been traveling and am coming into this late ... but my question is why are you using Plexiglas? If you use Polycarbonate, you can bend it without heating.

The ONLY disadvantage to polycarbonate over acrylic is that polycarbonate surface will scratch much easier than acrylic. Acrylic, on the other hand, will shatter when struck or bent, but is very hard to scratch (well, compared to polycarbonate).

I was at a local machine shop the other month, and they were working polycarbonate with their sheet metal working tools ... shear it, put a 90° bend in it, mill it ... all without problems.

Regards,

Rick

I'm rather new to this stuff. So most of my information comes from a buddy who did a some Acrylic work 15+ years ago. Although I was doing some reading on Lexan my original post. It certainly sounds like it's easier to work with, cost being the major down side.

Does the Lexan discolour (turn white) when you bend it without heat?

I've worked extensively with Lexan at work. It will snap or shatter if bent more than a couple degrees without heating. Also, the heating must be done gently, or air bubbles and\or white discoloration.