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Unread 01-16-2017, 08:17 PM
ollien ollien is offline
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How to bend lexan for a hood?

The title says most of it. We want to bend a piece of lexan to create a hood for a shooter. We don't have access to a brake. How can we curve this piece safely?
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Unread 01-16-2017, 08:28 PM
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Re: How to bend lexan for a hood?

Light Heat and patience
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Unread 01-16-2017, 08:29 PM
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Re: How to bend lexan for a hood?

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Light Heat and patience
How do I know when to stop heating?
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Unread 01-16-2017, 08:34 PM
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Re: How to bend lexan for a hood?

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Originally Posted by ollien View Post
How do I know when to stop heating?
If you want a sharp bend, when it easily flexes(I highly recommend a heat strip for this kind of bend). If you want a gradual bend, the only advice I can give is to buy extra polycarb and practice. Maybe some kind of radiant heater. Maybe thermoform/vacuform it.
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Unread 01-16-2017, 08:47 PM
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Re: How to bend lexan for a hood?

how thick is the material? We usually use polycarbonate that is a tad thinner than 1/8" thick. It will bend (and spring back) easily for things like that. If it's supported with an aluminum frame, then it will mostly hold it's shape.

If something looks kind of difficult to make the way you have planned, maybe you could figure out a different way to build it?
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Unread 01-16-2017, 08:59 PM
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Re: How to bend lexan for a hood?

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Originally Posted by MrForbes View Post
how thick is the material? We usually use polycarbonate that is a tad thinner than 1/8" thick. It will bend (and spring back) easily for things like that. If it's supported with an aluminum frame, then it will mostly hold it's shape.

If something looks kind of difficult to make the way you have planned, maybe you could figure out a different way to build it?
I'd have to check when I get back to the lab tomorrow, but if memory serves me right, it's 3/16"
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Unread 01-16-2017, 09:00 PM
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Re: How to bend lexan for a hood?

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Originally Posted by ollien View Post
I'd have to check when I get back to the lab tomorrow, but if memory serves me right, it's 3/16"
Ouch! That thick is hard to bend large pieces via heat properly.
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Unread 01-16-2017, 09:14 PM
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Re: How to bend lexan for a hood?

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Originally Posted by RoboChair View Post
Ouch! That thick is hard to bend large pieces via heat properly.
What thickness would you recommend? 1/8?
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Unread 01-16-2017, 09:28 PM
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Re: How to bend lexan for a hood?

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Originally Posted by ollien View Post
What thickness would you recommend? 1/8?
We had a lot of success with 1/8" last year. A lot of our robot, including the bellypan were polycarb. We mostly just used a vise and heat gun (be careful so it doesn't start bubbling). A continuous curve might be a little trickier than a one-place bend, though.
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Unread 01-16-2017, 09:47 PM
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Re: How to bend lexan for a hood?

We either cut several pieces with that profile and then bolt them together (with our without spacers in between) or create the profile with sheetmetal and spacers then line it with a thin piece of lexan that is zip-tied to the spacers.
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Unread 06-15-2017, 07:08 AM
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Re: How to bend lexan for a hood?

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Originally Posted by bhsrobotics1671 View Post
We either cut several pieces with that profile and then bolt them together (with our without spacers in between) or create the profile with sheetmetal and spacers then line it with a thin piece of lexan that is zip-tied to the spacers.
I'd recommend this as well. We also used Churro to create this profile and zip-tied the lexan to that this year. Simple yet effective.
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Unread 01-16-2017, 09:53 PM
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Re: How to bend lexan for a hood?

If you're just using it for a shooter I can't imagine you need too large a radius. It should be pretty easy to find something with a similar curve (pvc, lunacy wheels, etc) in your build space that you could mold the lexan around after heating it. This will be a lot easier than using a vise, and provide a clean curve.
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Unread 06-15-2017, 07:47 AM
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Re: How to bend lexan for a hood?

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Originally Posted by RoboChair View Post
Ouch! That thick is hard to bend large pieces via heat properly.
We have heat bent 1/4" in the past. We use a heat gun to heat it up and then bend it either on a table or by hand with gloves. Always wear gloves and safety glasses while bending polycarb. The heat gun is very very very hot.
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Unread 06-15-2017, 08:06 AM
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Re: How to bend lexan for a hood?

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Originally Posted by ollien View Post
How do I know when to stop heating?
Hard to tell when to stop, it's really more by feel, but my general rule has been if you start getting bubbling in the polycarbonate you've gone too far (though it doesn't really hurt anything, just looks bad).

Quote:
Originally Posted by arichman1257 View Post
We have heat bent 1/4" in the past. We use a heat gun to heat it up and then bend it either on a table or by hand with gloves. Always wear gloves and safety glasses while bending polycarb. The heat gun is very very very hot.
While I agree this does work, it takes an incredibly long time, especially if you have a wide piece of material you're trying to bend.

Quote:
Originally Posted by JoaquinC View Post
In the past we have used multiple mounting points along the arc of the hood as @Sarakiro was suggesting. As long as you use thin enough material, the Lexan should just flex along the curve (no heat necessary).

*snip*

2016: http://i.imgur.com/AxbqX2n.jpg?1
2012: http://i.imgur.com/GlQIJxh.jpg
IMO, this is the best way to work with polycarbonate if you can use thin enough material. It's far easier to form an aluminum frame at the desired radius and attach polycarbonate to it than it is to bend the polycarbonate to the correct angle. The one caveat I will add to this is that depending on the application, you may need to add supporting rods to maintain the shape consistancy of the polycarbonate (like in the 2016 picture JoaquinC posted).
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Unread 06-15-2017, 09:01 AM
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Re: How to bend lexan for a hood?

My team bends polycarbonate ('Lexan' brand name) often. It is tedious and takes a long time. Plan to be able to heat it alternating to both sides. Cover the area you don't want bent nearby with steel to focus the heat on the bend areas.

Rather than use a heat gun, another alternative to heating plastic is to buy a PVC heating blanket. Designed to use rolled-up with PVC pipe, they also work flat, allowing you to heat up a large area of lexan for a large bend. Takes some practice.
https://www.google.com/search?q=pvc+...active&ssui=on

It nearly always results in a decrease in strength of the plastic. I suppose from changes in surface tension and residual stress.

Most of the time you can smack a lexan piece with a hammer and it won't break. Not necessarily true for a heat-bent piece.

I know that some engineers indicate the bent parts should be 'annealed' that is, kept at a high temperature for a while, to remove residual stresses. Its tempting to cool the area with water, but that will add more stress, making it weaker.

Surprising trick, you can view some plastics (and glass) with polarized sun glasses and see where stresses reside because they polarize too, making them visible.

Quote:
Originally Posted by cbale2000 View Post
if you start getting bubbling in the polycarbonate you've gone too far (though it doesn't really hurt anything, just looks bad).
The bubbles are because polycarbonate, like most plastics, absorbs water. The bubbles are steam. They occur at 212F, where the deflection temperature for polycarb is more like 270-280F.

If you don't want bubbles, you'll have to heat the plastic more slowly, to dry it before you bend it. Because 212 always happens before 270.

Plastics companies put lexan in a drying room 48 hours before forming. I don't have one of those...

And like everyone else has said, wear gloves, have water nearby. We spend much time encouraging safety in FIRST, with eyewear and earplugs, tool-guards. But by far the most common injury in most shops is a burn.

Last edited by hrench : 06-15-2017 at 09:19 AM. Reason: added the bit about the heating blanket
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