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Old 07-15-2009, 06:08 AM   #1 (permalink)
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Coroplast Kammback: joining or bending?

Now that I have a sheet of coroplast to fool around with, I'm wondering how to actually construct the Kammback. Should I make it out of three pieces (top + 2 sides), or should I make it out of one piece? In the first case, I'll have to find a way to join the pieces: screws, glue, ??? In the second case, I have no idea how to safely bend a 5mm thick piece of stiff coroplast. Should I heat it? On the outside, or inside? What happens when it cools? Will it try to straighten out again, will the bend be strong?

Any help, please?

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--Adam

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Old 07-15-2009, 12:51 PM   #2 (permalink)
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I haven't bent any coroplast with a heat gun but i'm guessing you'll only want to heat the inside of the bend. The skin of it is so thin that if the outside was heated it might stretch and deform and end up a mess. Also, the internal ribs will complicate matters by running along a different line than the bend you want. Murphys Law remember?? lol!
So i'm guessing you'll want to make a series of little bends close together so you end up with one big bend.
As i say, i havent done this but i have experience working with materials so it's an educated guess, subject to correction of course.
I have a few sheets of coroplast lying in my shed. I just need to find the time to use it! I also got some foam pvc sheet for my future kammback and wheel skirts: Foam PVC Sheet - 365 Plastics - Access Plastics Limited
I used some to blank off my fog light blank inserts and it bent well over the gas hob. Held its bend too. Plus it looks almost stock, apart from the screws.....
I figured it would look better than coroplast and would form better too. It was 20 euro for an 8'x4' sheet. Again, between working nights and looking after the kids, i don't get much ecomodding time.......
Unlike you, Adam. You're powering through this ecomodding at some rate!

Best of luck,

ollie

Having said all that i'd try bending the coroplast instead of joining. It's going to be harder to get the join to look respectable, what with brackets, screws and the edge itself. Plus, the bent coroplast will be more rigid and a little lighter without the brackets of joined coroplast.
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Old 07-15-2009, 02:05 PM   #3 (permalink)
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Quote:
Originally Posted by vtec-e View Post
So i'm guessing you'll want to make a series of little bends close together so you end up with one big bend.
So maybe I'll try bending it around a pipe? Then it won't be a crease, but it'll be nice and rounded.
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Again, between working nights and looking after the kids, i don't get much ecomodding time.......
Unlike you, Adam. You're powering through this ecomodding at some rate!
Thanks I spent a lot of time getting ready, now I really want to get as much done as possible before our long trip to Romania in mid-August.
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Old 07-15-2009, 05:31 PM   #4 (permalink)
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Got an oven that your complex shape will fit in?

Bend up a section of chicken wire, to use for a form (mold) then lay in a sheet of coroplast. Put it in the oven (find out what your Coroplast is made of, then find the melting temp for it) and heat it up. Let it cool WITHOUT opening the oven, and once it's back to room temperature, it will have a memory of the shape that you melted it into.

To join sheets to make them bigger, there are two ways. To join lengthwise (holes facing each other) you use plastic sticks in every couple holes and then slather some plastic epoxy between them, scrape off the excess when they're mated.

For the other direction, you take a couple old wire coat hangers, straighten them out, and bend them entirely in half, with no loop at the end. (So that the length of the hangers is parallel as good as you can get it.) Cut a notch into the corrugation of about 1/2" on either side of both sheets, slather the hanger with plastic epoxy and slide it in. Brush epoxy down the length of both sides of the seam and let it harden up.

(Plastic/Rubber cement also works.)
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Old 07-15-2009, 06:03 PM   #5 (permalink)
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If you make it 3 pieces, use a piece of wood internally on the corner to attach the pieces together. The wood may need to be contoured to accomadate your shape.

If an angular bend is desires, you can remove both inner skin & ribs out of the desired area. I would probably heat the outer skin also. You may want to support the bend with some bent sheet metal as well.

Practice first.

Don
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Old 07-15-2009, 06:55 PM   #6 (permalink)
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I bent coroplast using a propane torch and a straight edge. I clamped down the angle iron along the bend line and ran the propane torch flame along the bend line fairly quickly, with two passes. Then I immediately grabbed the plastic and bent it around the corner.

I used a steel(?) angle iron and an aluminum bar for straight edges. The bend is very strong.

You could also use separate parts and zip tie them together.
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Old 07-15-2009, 08:04 PM   #7 (permalink)
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Coroplast can be bent with the grain or up to about 30 deg either way by slitting the inner surface. Use a blunt-tip knife to save the other surfaces, and hold it at an angle so the cut edges slide over each other. For other forming, it is best to heat just the inside with a hair dryer or hot air gun. Sharp creases can be made by scoring with a blunt tool, and then running a bead of hot glue down the groove. That will first heat the polypropylene, and then help hold the shape. Oven heating can give full vacuum forming options, but you will probably make a large pile of scrap getting the process adjusted.
BTW, I have actually done lots of this stuff, not just guessed at it. Silicon seal works for bonding - I've never seen "plastic epoxy." Polypropylene is among the "waxy plastics" - hard to glue. COROPLAST HPV BODY CONSTRUCTION
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Old 07-15-2009, 09:25 PM   #8 (permalink)
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Coroplast can be bent with the grain or up to about 30 deg either way by slitting the inner surface. Use a blunt-tip knife to save the other surfaces, and hold it at an angle so the cut edges slide over each other. For other forming, it is best to heat just the inside with a hair dryer or hot air gun. Sharp creases can be made by scoring with a blunt tool, and then running a bead of hot glue down the groove. That will first heat the polypropylene, and then help hold the shape. Oven heating can give full vacuum forming options, but you will probably make a large pile of scrap getting the process adjusted.
BTW, I have actually done lots of this stuff, not just guessed at it. Silicon seal works for bonding - I've never seen "plastic epoxy." Polypropylene is among the "waxy plastics" - hard to glue. COROPLAST HPV BODY CONSTRUCTION
It's a 2-part epoxy that comes from most hardware stores. Isn't Coroplast made from PVA/PVC?
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Old 07-15-2009, 10:19 PM   #9 (permalink)
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Well, "Coroplast Classic' is polypropylene, but there's no reason not to extrude almost any thermoplastic through the same sort of die. I've seen polycarbonate in thick panels for greenhouse use, for instance. Fresh from the factory, the regular signmaker's grade has a "Corona Discharge" treatment to help ink adhesion. I've gotten the very common WEST epoxy to stick, but not very well.
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Old 07-15-2009, 11:47 PM   #10 (permalink)
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Piwoslaw -

Quote:
Originally Posted by Piwoslaw View Post
So maybe I'll try bending it around a pipe? Then it won't be a crease, but it'll be nice and rounded.

Thanks I spent a lot of time getting ready, now I really want to get as much done as possible before our long trip to Romania in mid-August.
I have *no* idea if this would work, but I was thinking of using a metal pipe and a heat gun. The heat gun would be aimed *into* the pipe to heat it up. If you were lucky, you could get it to have uniform heat. Hmmm, probably have to take turns heating the pipe from each end to maintain pseudo-uniformity.

But the other methods stated are proven,

CarloSW2

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