Plastic bending tips

[killbucket]

First off, what about Mom's kitchen tools?
I get asked about his quite a bit- everybody has a kitchen stove, and some have wondered: Can this thing help me make parts?

The answer: NO. Kitchen stoves are designed for the heating and cooking of things that are safe to consume and SMELL, i.e., Steak Tri-tips, chocolate cakes, etc. that being said, I've used my trusty Amana for worse...same goes for the ever-popular over-the-toaster trick.

Heating PLASTIC in your home immediately sets up DANGEROUS conditions. MOST plastics "out-gas" when heated, releasing volatile fumes, corrosive agents, not the building blocks of life. Sometimes, the mixtures can be deadly! A lot of plastics (thermosets) just won't melt or get soft, they'll char and go to flames first.

Like most Thermoplastics, once MELTED, ABS will puddle and bubble, and then
"spectacularly burst into sticky flames."

Yes, Mom would be mad.
So DON'T DO THIS yourself. Consider this information on how I play with fire, nothing more.
Most of what you need to know about ABS:
http://en.wikipedia.org/wiki/Abs_plastic
Buried in this info (actually in a link) is the "heat deflection temp" for ABS plastic. It's 185 degrees Fahrenheit. That means, at a uniform temp of 185, it can be deflected. Fancy way of saying "bent".

But you don't really want to fully heat a sheet, just bend it to your will.


This is an electric bending strip. Made of a teflon/fiberglass mesh, with a heating element woven into it.
http://www.interstateplastics.com has these in different lengths, this is a 24".
It's CHEAP UNDER $50 - get one, and skip playing with your toaster.


Making STRAIGHT bends is much easier if there is a groove ('kerf') routed into the backside of the bend. This is industry practice for making plastic structures.

It just takes a bit longer to heat through without, and a bit more care is required to get the bend positioned correctly, and be straight. Be sure to have scrap available to test with, that way you'll know how your actual part will behave in process.

Depending thickness, time will vary for getting the plastic to the right temp. Note the digital timer. By putting it in count-up mode for the first bend, I determined that 2.5 minutes were needed for full heating of a section this thick.

Then I just set up a count-down for the next parts, and was able to carry the timer while I did other small tasks.
ABOVE ALL, you don't want to become distracted and forget about plastic in-process. It only takes ONCE to really, really change your future. Please be diligently careful.



The finished bend.






So what ABOUT using kitchen appliances?

She's off, the mutts are locked outside, and the stove in the kitchen just got done making me some frozen meatpies from Costco. Rather than shut it off, I turned down the temp to 320.

I know, only 185 does the job, but it would take much longer to soften the part. The trick is to get the ambient temp around it a bit higher in the heater, so it all softens uniformly.

My example here is the bands for making a drum, or Trommel, magazine for my treasured Marui Thommy:

The drums were made in 50- and 100-round versions. In real life, both were more deadly to the shooter than the shootee, they jammed like crazy, leaving you with at best, an improvised club...but I digress.

Rather than fight a strip of 3mm ABS into a band, I'll give it a shot of BTU's, and wrap it around something round, like this stack of MDF disks:


The strip, 20" x 1.70" was laid lengthwise in the oven on lower rack, and the oven light snapped on.
I only wanted the material SOFT, not MELTED! The first experimental parts looked more like egg noodles than drum bands.

So I watched as the strip "relaxed" and then flipped it over, and closed the door for a few more seconds.

Then, it was quickly snatched out and slapped around the form. Grabbing from the oven was done with bare hands, as the contact time was low, and heat doesn't "transfer" from ABS quickly, but holding it against the form (after a slight stretch to make sure it laid flat) required some oven mitts.
By the fourth try, I had it down to a process.


Finished bands, after cooling. even though I needed bands of varying diameters, I only used the one form, as ABS is pliable enough to be final-shaped in or out at gluing.



QUESTIONS?

I'm working on a freebie, WheelieKing frame, made from 1/8" ABS. you'll need to be able to do two bends to complete it (after cutting the part out). Hang tight, I'll get it posted up in a jif.

edit: Here ya go THIS IS MY OWN CAD DRAWING, BASED ON THE ORIGINAL LOCATIONS FOR THE STOCK HARDWARE.

This is meant as a starting point only, of course!
http://www.air-sharp.com/wkstartfile.dwg

[killbucket]

A quicky thermo-formed Wheely King crawler frame. Made of 1/16" ABS sheet, it weighs a scant 1.7 oz.

[Stormin2u]

Nice thread.

[killbucket]

thanks!

[5150bronco]

you are on here. that is awesome. you get around.....lol

ha ha. you mentioned toaster, i am a rookie i guess. nice build. I want to build a skid plate to mount a tranny for my scaler. i could actually find a pic on here but that is what I want to do. no really big bends or anything.

thanks Kill.

[killbucket]

Sounds like a good first project. Start by making a cardboard fake (cereal boxes are perfect material), and then transfer the dimensions to your material.

If you can add CAD to the project, then you can print out the final design, and use it as a stencil for making the part:

TURBOcad:
http://www.turbocad.com/Products/Tur...0/Default.aspx
Just $149.95, but I got mine at Fry's for less than $100.
EASY to learn, comes with tutorials. You will be designing stuff the first day!

So you draw what your heart desires, then print it at 100% actual size.


A step bit and a centerpunch are handy items to have for this project. we'll see the Scrollsaw a bit later...

Not seen in the next pic very well: First cover the sheet stock with contac paper. When you go to remove your layouts, you'll be happy you did. Get some spray adhesive and fix the prints to your chosen material:


Then mark and drill the holes. Do this with the parts still in as large as possible chunks. This will minimize fixturing, you can save a bunch of time doing this. Then cut out your parts using a Scrollsaw:


TOP SECRET: Use these, and only these, blades:
Vermont American #30423
(5" long, 11.5 teeth per inch, .045 blade depth, .017 thick.)
Cuts ABS and PVC like butter. Slow speeds are best for ABS.

Your freshly cut parts. If you're proud of your work, take pictures and show the world. Maybe show others how you did it:


Do a test assembly to make sure no fitting is needed.
The worst time to find out you needed to file an edge is after it has nice sticky glue all over it.

If everything fits, grab the glue or fasteners.

Maybe a coat of paint and some doodads:


You can make just about any bracket or other part you might need this way.

[5150bronco]

where is a good scroll saw at?

I could just cut the parts out than instead. I would need to figure out how to get the parts together, when one side will be 45 degrees against the flat bottom piece.....
huh.

thanks kill.

[killbucket]

You can get 'close' with a rough flat file, and the glue's thick enough to fill gaps. The TRICK, is to make a simple carboard fixture to hold the proper angle for three or four minutes while it set up.

[5150bronco]

Originally Posted by killbucket

You can get 'close' with a rough flat file, and the glue's thick enough to fill gaps. The TRICK, is to make a simple carboard fixture to hold the proper angle for three or four minutes while it set up.

okay. so file half way through and than bend than fill with glue? what kinda glue?

what about ambroid pro weld?

[killbucket]

OH..you mean to make a kerf for a bend.

Minus a good router, or a very short area to file, I'd just skip the vee kerf, and practice bending full thicknesses.

[5150bronco]

Originally Posted by killbucket

OH..you mean to make a kerf for a bend.

Minus a good router, or a very short area to file, I'd just skip the vee kerf, and practice bending full thicknesses.

okay. ha ha. kerf...., is the half cut terminology.

so what were you thinking than? when you said i could get close with a rough file?

thanks.

[insanityxj]

This is some great info!

[killbucket]

I meant doing an assembled, mitred joint to join TWO panels. You were referring to making a bend in ONE.

but if you needed a short kerf across a small panel, a file would be the tool. Just tape off the line you want, and slowly work a groove into the plastic between the tape strips.

[5150bronco]

[QUOTE=killbucket;2230774]I meant doing an assembled, mitred joing to join TWO panels. You were referring to making a bend in ONE.

can you explain this you wrote?

yes, i wanted to make one bend on each side. than in the middle i will mount the tranny. thanks man.

[killbucket]

I was talking about THREE parts to make what you're doing, and you were saying take ONE part, and bend it twice to make a frame, like I did above.

[5150bronco]

Originally Posted by killbucket

I was talking about THREE parts to make what you're doing, and you were saying take ONE part, and bend it twice to make a frame, like I did above.

AH, I see. i need to figure out how to bond the 3 parts together. suggestions?

what you think about the pro weld?

[5150bronco]

Hey Kill, i started a thread and I am going to give it a shot on building a bender for me. your thoughts always welcome.

[killbucket]

Experiment. I've never used it.

[5150bronco]

Originally Posted by killbucket

Experiment. I've never used it.

i will. I think, and I already have everything disassembled. i would like to bounce ideas with you once I get pics to not take over this thread. thanks.

[killbucket]

Do NOT try to 'make' a heating element out of anything...toaster, curling iron, old TV set (some were good space heaters!).

REAL heating strips are WAY cheap, and your lawyer will have something to 'work with" when your dependents sue Oster.


Get one of these, it's what I have:
http://www.briskheat.com/p-152-rh-pl...ip-heater.aspx
JUST $37!


EDIT: Unless you go to TAP, where you will pay $70. No joke.
http://www.tapplastics.com/shop/product.php?pid=169