bending plastic strip without heat.

18 posts in this topic

Posted (edited) · Report post

last week i was trying to explain to another member of this forum how i do my bending of plastic for the Art Morrison frame i built.

im not always the best at just explaining things without pics so here is a quick tut with pics i did for him and anyone else who will get use out of it.

List of tools and supplies you will need.

- sheet of paper - this will be used to draw your template.

- plastic strip of your needed size.

- .02 thickness plastic sheet stock. - this is to hold your shape

- flat file or rotary tool with your desired cutter. - as you can see in the pics i used a rotary too in a shaping table. highly recommended if you do a lot of scratch building.

- sharp hobby knife or serrated blade

- pair of small pliers

- your favorite glue. -

- Filler

- High Build Primer (Dupli Color High-Build Primer is my favorite)

- sand paper 320 & 400 grit.

STEP 1) Pattern Making - i omitted the pics in this step as its pretty much self explanatory. draw you desired shape on paper to use as your template.

Step 2) Shaving. - in this step you are going to shave .02 thickness from where your bend will be.

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Step 3) Scoring - what you are going to do in this step is score some breaking lines. when scoring lines you only need to go a 1/4 depth into the plastic. you can go more if you want but no more than 3/4

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keep your score lines evenly spaced at about 1/16 or 1/8 apart and as square with the plastic as you can.

Step 4) Breaking - this step can be tricky for some. you will want to break the plastic on your score lines but not to the point where you break it in half.

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at this point it becomes a delicate process. as you can see in the pic below there is not a lot holding the plastic together and can easily break in half so handle with care.

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what i found when breaking score lines is to have two pairs of small pliers. one will hold the plastic while the other does the breaking. there are other tools that can be used from tweezers to jack knife or your fingers but with less control.

this step is not a hard step but it can be delicate one so practice before starting your build.

Step 5) Gluing - this is where step 1 and 2 come in. i highly recommend using plastic cement over fast drying glue.

lay your plastic strip down following your templates pattern and secure it to its shape with whatever you use. (small bottles, pins, cinder blocks etc). you will now need to cut a piece of plastic and glue it into the cavity from step 2

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the piece of plastic you just glued in will give it strength and hold the shape.

when the glue is dry do your trimming and sanding.

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the frame below was built using the same techniques i just mentioned above. you can see the breaks and filler pieces i used in building this frame.

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the remaining steps left are your filling sanding priming and painting. with primer i prefer Dupli Color High Build Primer its a very easy sand-able primer that works great as a filler of minor imperfections.

in the future when time allows me to do it i will make a much better tutorial with more pics and info.

Thanks for looking and im always interested in your feedback.

Edited by Marcus M. Jones

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Posted · Report post

Thanks for the post Marcus!

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Posted · Report post

have you tried doing this with the kerfs (cuts) to the inside of the bend, as you would when bending wood? there's a specific formula for how many kerfs and how far apart to obtain a given radius curve, but i don't have it at hand. placing the kerfs inside the curve reduces the likelihood of breaking and gives you gluing surfaces to hold the stock in place without having to add fishplates. cabinet makers use this method all the time for making curved faces out of plywood/lumber. you can even bend drywall using this method.

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Posted · Report post

have you tried doing this with the kerfs (cuts) to the inside of the bend, as you would when bending wood? there's a specific formula for how many kerfs and how far apart to obtain a given radius curve, but i don't have it at hand. placing the kerfs inside the curve reduces the likelihood of breaking and gives you gluing surfaces to hold the stock in place without having to add fishplates. cabinet makers use this method all the time for making curved faces out of plywood/lumber. you can even bend drywall using this method.

I agree... placing the kerfs inside the bend makes more sense. Like Curt said, no reinforcing plates needed, and that's how woodworkers bend wood. The only difference to the tutorial posted here would be that you'd have to use a razor saw to make the kerfs instead of just scoring them with a blade, because you actually have to remove some material (the amount removed in each kerf cut is equal to the thickness of the saw blade) in order to be able to make the bend.

Once the bend is made, flood the area with liquid glue, that will "weld" all the kerfs together and you'll wind up with a pretty strong piece.

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Posted · Report post

kerfs cuts would be the better way of bending but like Harry said you have to physically remove plastic. for a builder who doesn't have loads of experience or the confidence this could become a bad experience for them. even though it is a little more work with filling and adding fishplates <= didn't know what they were called in till you said it Curt) it does simplify things for the new builders a little bit.

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Posted · Report post

Another way to go if you make the cuts on the inside of the bend (instead of the outside) is instead of making a series of kerf cuts with a razor saw (making a 90 degree bend would take a lot of very closely spaced kerf cuts), use a file that will create a "V" shaped notch, file several notches, then bend. The notches are larger than the saw blade kerf cuts would be, more material is removed, so fewer notches needed to get a tight bend.

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Posted · Report post

And to add more to this,Micromark sells a tool (mostly intended for model ship builders) to bend wood strips. I believe thy suggest plastic bending too.

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Posted · Report post

Hey Guys,

Both methods would be great to build the "gooseneck" portion of the trailer frame on this tractor drawn aerial. This style has been a favorite of mine for years, but "engineering this portion of the project has kept me from starting it... YoungAmerica.jpg

Actually, an application of the kerf technique to both sides of the frame material would be needed to accomplish the "gooseneck" effect.

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Posted · Report post

if i were building something that large, with intricate curves, i'd rough out the desired pieces in sheet stock, laminate them and final shape them by sanding. that way, you're not "building in" any stresses that might come back to haunt you.

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Posted · Report post

Marcus I'd seen that chassis before here and wondered how all those excellent bends were done. Thanks very much for sharing and being cool about other folks expounding upon your idea. Well done.

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Posted · Report post

Marcus I'd seen that chassis before here and wondered how all those excellent bends were done. Thanks very much for sharing and being cool about other folks expounding upon your idea. Well done.

getting as much info out there for the builders to decide which is best for them is what this forum is for right?

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Posted · Report post

Absolutely but you'd be surprised how often folks take it as a personal attack. We do get out share of drama around here.

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Posted (edited) · Report post

Thanks for the how-to, Marcus! I'll be using your technique on a Cadillac project I'll be posting soon.

Edited by BKcustoms

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Posted · Report post

Thanks for the how-to, Marcus! I'll be using your technique on a Cadillac project I'll be posting soon.

i'll be watching for it!

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Posted · Report post

Outstanding frame and tutorial. Thanks for posting it.

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Posted · Report post

Nice tutorial! thanks marcus!

cheers

bryan

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Posted · Report post

Man this is so kewl, I have been looking for a better way to twist my plastic, an do some frames, thanx man, thank you everyone for the other ides too...

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Posted · Report post

I agree. Thanks for the tut. I understand all the different angles of the other input and see where other methods could work better in different situations. I have a project that stalled out a while ago because of a frame customizing problem and here is my solution...

Thanks for all the input...

BTW (i was a sheetrocker for 25 years) the best way to bend drywall is to soak it with water and bend it very slowly till you get the curve you want. It is a major hassle but looks great when it's done...

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