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Bending plexiglass, lexan, etc.

2icebitn

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I'm building an experimental litter box. I need to bend up some clear material. I remember doing this in shop class, they had some sort of resistance wire contraption, you placed the plexiglass in position, the element would glow, softening the material along a line, along which it would bend. I guess I could just but some nichrome or kanthal wire on ebay and build something. Just putting this out there if there are any suggestions.
 
I make a wooden jig and use a heat gun (carefully) to form the material to the jig.
 
Well I have a small bending brake. I suppose a heat gun could work, perhaps with some wood used to mask off parts of the material. I'm tired of smelling cat piss and buying so much litter. I'll lick this problem, maybe even have it patented (yeah right).
 
With practice you can use a mapp gas blow torch and really have fun without bubbling the plexi. I generally don’t free bend, but use wood as a form to bend straight lines, then adjust by hand. When I want a less artsy look, I actually own a heated plexi bending table that has an embedded heater that only heats up the line to bend and is temperature controlled. If you want to drill holes afterwards, you should buy special plexi drill bits. Using a wooden bit in reverse is still taking a chance and when I was starting out I waisted hundreds of dollars in cracked plexi learning that lesson. Be careful some plexi cutting tools can be expensive. I think my special plexi table saw blade cost more than my actual Ryobi table saw.
 
Why would I use mapp gas? Propane or butane maybe. The heat gun should work. Presumably you just alter the drill bit angle as you do when drill sheet metal, lots of lubricant. And drill some, clear the hole. Perhaps attempt to plunge and do it all in one shot is one reason for cracking. You could just heat the bit and melt a hole I guess. Another option is to bore a hole with a homemade boring bit similar to a fly cutter. This way you shave out a hole and impose less stress comparatively.
 
Mapp is easy enough to get and burns hotter than propane. So with practice you can get more creative in the bending. I have made many different custom computer display cases this way.

For drilling, anything other than a specialized plexi drill bit risks micro cracks (or big ones) which can eventually split the Plexi. I tried a lot of different techniques and finally gave up and bought the real thing to remove the risk of splitting $100 pieces of 1/4” and 1/2” plexi.
 
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You cannot buy MAPP gas. It hasn't been made in ten years. If you are lucky enough to have some left over, don't waste it on this.

There are plastics that you can bend cold in a brake. But for hot forming perspex or lexan, your brake is probably too much of a heat sink.

By the way, if you want to go the resistance wire route, get a hair dryer from your local thrift shop. It's full of it. The wire is coiled, but you can pull it straight.

When I make drills for this kind of material, I sharpen them with a 90° tip. I like to use carbide if I can, and use water based coolant. I have never bought a drill specific for perspex, so I'm not sure if that's what they sell. Square end mills work well if you have a milling machine but you really have to get the speed and feed right and use coolant.
 
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I just checked. Your right. I’ve been using “Map Pro” which is propylene, at some point homedepot switched on me and I never noticed. Why bother modifying your drill bits, just buy the right ones for plexi online.
 
I just checked. Your right. I’ve been using “Map Pro” which is propylene, at some point homedepot switched on me and I never noticed. Why bother modifying your drill bits, just buy the right ones for plexi online.

A lot of us were fooled by the MAP/Pro stuff. It does burn hotter than propane, but nowhere near as hot as MAPP. I still have a few bottles of MAPP. You can't beat it for sweating copper with silver bearing solder.

When you have as many drills as I have, the only reason to ever buy one is if you actually run out. I do run out of #21 and #7 occasionally. I've got a huge box of rusty old high speed jobbers that are prime for modification. The tips are pretty trashed on most of them if they aren't flat out broken. The only trouble is that the older ones don't always have standard twist, so they don't work in the Drill Doctor. But that's what pedestal grinders and good hand-eye coordination are for.
 
So I'd place some thin balsa wood between the material and the brake if that's an issue.

I don't think that works. You'd have to change the pivot distance of the brake. I could be wrong, I'm falling asleep and don't have the drive to go look at a brake to make sure I'm thinking about that correctly.

You could make a simple wooden brake with a couple of old door hinges.
 
My only advice on this is to use a form. Acrylic, when headed to pliability is likely to "cup" or "bow" otherwise, At least that's what's happened with me.

Acetylene+air is a pretty good alternative to MAPP, but you shouldn't need to go that far for bending acrylic.

If the shape is complicated, DIY vacuum-forming setups are inexpensive and great if you need several copies of a part.
 
Nothing in this project is super critical. A resistance element bending jig would be ideal, if I were making duplicates, but. I'll cross that bridge maybe.
 
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