Author Topic: Bending smaller pieces of flat acrylic, polypropylene etc  (Read 13082 times)

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Offline nzo

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Bending smaller pieces of flat acrylic, polypropylene etc
« on: November 01, 2011, 09:25:54 pm »
I've just discovered flat plastic sheet as a useful alternative material to metal in fabricating smaller items of between 4" and 8" in length/width. (I don't yet have a CNC plastic printer).

Has anyone here mastered the art of bending these plastics without investing in expensive heaters/benders?

I'm talking about simple 90° right-angle bends.

Tricks and tips welcome :)

Thank you!
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Offline IanB

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Re: Bending smaller pieces of flat acrylic, polypropylene etc
« Reply #1 on: November 01, 2011, 09:33:57 pm »
I have not done it, but I would use a temperature controlled hot air gun and some suitable forms to bend around. If you want a right angle bend, construct a right-angle form with a rounded corner to use as a pattern. Then lay the sheet on a flat surface and carefully heat along the crease until it is bendy. Possibly cover the flat parts each side of the bend with foil to keep them cool. When the sheet is soft, carefully bend it along the crease against the form and hold it against the form until the plastic hardens again. Use your ingenuity and experiment a bit.
 

Offline Jimmy

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Re: Bending smaller pieces of flat acrylic, polypropylene etc
« Reply #2 on: November 02, 2011, 12:18:52 am »
I bend pvc conduit with a lpg gas torch. If I was to try bending a flat sheet as you described I would construct a jig to hold the flat sheet or clamp it to a table with the fold line hanging off the end then heat the bend line with the torch moving fairly quickly at an even pace so it heats up evenly. Then once it has finished bending to the 90 deg after 20sec rub a wet rag on it to cool it down.
 

Offline mikeselectricstuff

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Re: Bending smaller pieces of flat acrylic, polypropylene etc
« Reply #3 on: November 02, 2011, 12:26:50 am »
All you need is a linear heat source - for larger sheets I use an infrared bathroom heater with the reflector removed, for small pieces, a flat nozzle on a hot air gun.

For really small pieces you can use a soldering iron, just hold the plastic a few mm away.
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Offline sonicj

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Re: Bending smaller pieces of flat acrylic, polypropylene etc
« Reply #4 on: November 02, 2011, 01:30:17 am »
i've tried bending plexi (1/4") with just a heat gun. didn't turn out too good... i think a jig and a oven would have worked better with a piece that thick.

i have had good luck with polishing out scratches though. this piece looked terrible when i found it.
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Offline IanB

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Re: Bending smaller pieces of flat acrylic, polypropylene etc
« Reply #5 on: November 02, 2011, 01:51:13 am »
i have had good luck with polishing out scratches though. this piece looked terrible when i found it.
Metal polish?
 

Offline IanB

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Re: Bending smaller pieces of flat acrylic, polypropylene etc
« Reply #6 on: November 02, 2011, 01:54:37 am »
infrared bathroom heater
Do they still sell those? I'm wondering if I've even seen one here in the USA.

Back in England I remember the electric bar fires they used to sell with exposed radiant elements. It's been in the back of my mind to try to find some replacement elements for those to cannibalize for resistance/heating wire. Once again, are they still available?
 

Offline sonicj

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Re: Bending smaller pieces of flat acrylic, polypropylene etc
« Reply #7 on: November 02, 2011, 05:20:52 am »
Metal polish?
pretty much.... i wet sanded up to 1000 grit, then used a tripoli compound on a spiral sewn wheel followed by a "final" type compound on a vented buff. ideally, one would use acrylic specific compounds and buffs, but i just used what i had on hand.
-sj
 

Offline nzo

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Re: Bending smaller pieces of flat acrylic, polypropylene etc
« Reply #8 on: November 02, 2011, 08:02:23 am »
Thank you all!

AFAIK the wire on the old-style heater elements is Nichrome. Rewound on a former the diameter of a knitting needle may do the job. I hear infra-red heater elements might work too, if the diameter is small enough.

I also came across this instructable: Poor man's 200 dollar plastic heat strip for pennies!

That's a fine descratch job sonicj.


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Offline mikeselectricstuff

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Re: Bending smaller pieces of flat acrylic, polypropylene etc
« Reply #9 on: November 02, 2011, 11:51:12 am »
infrared bathroom heater
Do they still sell those? I'm wondering if I've even seen one here in the USA.

Back in England I remember the electric bar fires they used to sell with exposed radiant elements. It's been in the back of my mind to try to find some replacement elements for those to cannibalize for resistance/heating wire. Once again, are they still available?

Yes - the bathroom ones have the element inside a silica tube, and as they are high wall mounted are safe.The elements are typically 8-10mm dia, so pretty good for line bending. You do need to under-run them though as they will be way too hot if run at full power.



http://www.heatinfrared.co.uk/Indoor%20Infra-red%20Heater.htm
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Offline robrenz

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Re: Bending smaller pieces of flat acrylic, polypropylene etc
« Reply #10 on: November 02, 2011, 12:09:12 pm »
If you use polycarbonate "Lexan"  it can be bent cold in metal bending equipment ( finger brake or press brake ). It also is much more impact resistant than acrylic "Plexiglas" and can be machined without cracking with normal cutting tools.

Offline nzo

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Re: Bending smaller pieces of flat acrylic, polypropylene etc
« Reply #11 on: November 02, 2011, 05:56:47 pm »
Quote
mikeselectricstuff: You do need to under-run them though as they will be way too hot if run at full power.

I've often wondered about that - how do you underrun something like this without using one of those variable mains transformers?

robrenz: I live and learn. Lexan sounds like an amazing material.
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Offline gregariz

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Re: Bending smaller pieces of flat acrylic, polypropylene etc
« Reply #12 on: November 02, 2011, 06:31:08 pm »
infrared bathroom heater
Do they still sell those? I'm wondering if I've even seen one here in the USA.

Back in England I remember the electric bar fires they used to sell with exposed radiant elements. It's been in the back of my mind to try to find some replacement elements for those to cannibalize for resistance/heating wire. Once again, are they still available?

heater wire is not so hard to obtain so you needn't become a canibal.

http://www.jaycar.us/productView.asp?ID=WW4040&keywords=nichrome&form=KEYWORD

I've also seen people pull wire out of a stainless steel flydoor and that seems to work ok as well... but that just seems like hardwork. Anyone dealing with hotwire foam cutters should have some.
 

Offline robrenz

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Re: Bending smaller pieces of flat acrylic, polypropylene etc
« Reply #13 on: November 02, 2011, 06:34:11 pm »
robrenz: I live and learn. Lexan sounds like an amazing material.

If you google polycarbonate you will see it is used everywhere, safety glasses, cd's, dvd's, water bottles etc. you can buy it in sheet form with cover paper on both sides in various thicknesses.  Lexan is a Dupont (US) brand name but it may be called Makrolon, Makroclear or others in other counties.


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