Instructables

Poor man's 200 dollar plastic heat strip for pennies!

Want to bend sheets, tubes, sticks of plastic?
Don't want to buy a 200 dollar heating base?
Build one for pennies! (free if you go dumpster diving)
 
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Step 1: Materials and tools

For a totally free unit, dumpster dive for these materials:
- Toaster oven (cylindrical, rod-like, non bent, heating elements)
- Sheet metal (I used old brass door kick protectors)
- Outlet plug (old extension cord or whatever)
- Light dimmer
- Wiring nuts (or soldering gun)
- Liquid electrical tape (optional)
- metal pipes (optional)

Tools:
- Garden Shears (or anything that cuts sheet metal)
- Dremel or drill
- Pliers

Step 3: Building the base/heat strip and wiring.

-Take the sheet metal (must be longer than the heating element, or series of heating elements if you wish to make the heat strip longer) and cut out tabs to be bent perpendicular to the rest of the sheet metal.
- Drill holes on the tabs to thread the heating element through.
- Wire one lead of the power cable to one lead of the dimmer switch, and the other lead of the dimmer switch to one lead of the heating element.
- Wire the other lead of the power cable to the other lead of the heating element.
- (Since the heating elements work on A/C current, you can disregard rectifying the current, and you can disregard which lead of the power cable goes to which lead of the dimmer or heating element.)

Optional:
- Mount metal pipes (with nuts and bolts or cut tabs on the sheet metal and bend them in towards the pipe) parallel to the heating element, with an about 1 inch gap from the element.
- Apply liquid electrical tape to seal any exposed wires (don't want to be electrocuted. I used tape)
drcrash7 years ago
You really shouldn't be using the output of the dimmer directly. You need an isolation transformer or a step-down transformer.

(A step-down transformer will supply isolation, as well as reducing the voltage.)

I think for a strip heater you only want about 2 or 3 watts per inch, so if you use a 12 or 24 v transformer and a resistance wire, you could adapt power supply designs for hot wire cutters.

An adjustable hot wire cutter power supply can be really simple---basically a 12 or 24V transformer on a dimmer, or just plugged into a router speed control.

Stainless steel fishing leader makes a good resistance wire for a hot wire cutter, and it's dirt cheap. ($1.50-2.00 for 30 feet at a bait and tackle place.) It'd probably be good for this, too. (For hot wire cutters, it's better than nichrome.)

You need a transformer that can put out several amps. Your average wall-wart can't do that, but maybe a 6- or 10-amp car battery charger would be about right.

This post over on rcgroups, about wires & power supplies for hot wire cutters, may be helpful:

http://www.rcgroups.com/forums/showpost.php?p=6769158&postcount=22

That's from this thread on hot wire cutters:

http://www.rcgroups.com/forums/showthread.php?t=628704

If you get the wire length and gauge right, you could use a fixed-voltage power supply with no dimmer or speed control. (Maybe a car charger, or maybe one of the converted ATX bench power supplies in some Instructables.)

You can make small adjustments to the heat by varying the length of wire that you actually electrify.

While using an iso-transformer could be a nice safety measure it is not necessary. Even commercial grade thermoforming heat strips typically do not use ac isolation. Think about it electric range burners do not use iso-transformers, they get direct ac line current through a thermostatic rheostat (which is what a light dimmer is). The same applies to toaster ovens. I speak from experience working in the plastics industry for many years. I have built multiple heat strips using the exact technique described in this article with great success. Just my $.2.
I'm sure you are very experienced in the plastic industry, but you mathematics is clearly lacking; "$ .2" is twenty cents, not two cents. Just my $ .02. XD
I'm sure you're great at mathematics, but your editing and grammatical skills are clearly lacking. You used "you mathematics" instead of "your mathematics," and a semicolon instead of a colon in your statement above. ;-)
mattman2 benwade6 months ago

the semi colon is grammatically correct in this case

tovey punkhead589 months ago
He was adjusting for inflation.
Since he has years of experience in the industry he's valuing his opinion at 10x the going value for opinions.
I don't think he did it intentionally, but I'm sure that it was subconscious.
Back in the 50s & 60s, all the kids I knew that put together model airplanes & cars had figured out that the transformer from their old electric train set would cut thru plastics like butter.. They just bent some appropriate sized wire into the most useful shape, screwed the ends to the transformer poles, and did all the custom modifications in no time. It took a bit of fiddling to move the plastic at the right speed & not burn it, but adjusting the transformer knob helped also. I doubt they could even sell electrain train transformers without a ton of sissified safety devices now, so probably a modern train transformer won't work without some real modification.
Most model train transformers can't do the amps for this, and will cut out on you. Some (mostly older) ones will, but you risk overloading them and Bad Things happening... especially if you don't use a thin, high-resistance wire like an appropriate size of stainless steel fishing leader. A bunch of rc guys have gotten bad results with model train and doorbell transformers, especially when combined with random cutting wires. (Guitar strings, etc.)
I wish I could remember the details, but we were only about 12 or 13 when this was going on, which puts it back to when dinosaurs ruled the earth. Al I really remember was the buzzing of this big black transformer as they turned the dial, and how the wire glowed bright red, and I think they had to dial it back to keep from making a mess of the melting plastic edge. Not being into the models myself, it was just an interesting thing to watch, for me. This was about 1958, and it might have been a more powerful transformer, since the kids I watched had unusually big model railroad setups, what we called "two-board" outfits -- several sheets of plywood and a lot of complicated routing & trains. They also used the transformer trick to cut up plastic to make little signs & buildings for the model trains. I believe they tried balsa wood also, but it burned too badly. Surprising we ever survived childhood without the EPA and the Consumer Product Safety Commission.
tovey smokehill9 months ago
>>>
Surprising we ever survived childhood without the EPA and the Consumer Product Safety Commission
>>>
A lot of People down those agencies. But just think how many injuries would occur with the current status of greed in Corporations and other businesses.
How many toys would be laced with lead and other harmful chemicals if the Government didn't step in and regulate those things.

Some argue that the market would take care of that. I have serious doubts about that. I'm of the opinion that the insistence for more and more profits without those agencies would cause an unending cycle of lower and lower quality and safety.

Remember how bad things got when the finance market was deregulated. And this was the second time that Wall Street caused a such a deep world wide economic downturn.

If they do their job correctly, we will have all the advantages of a Free Enterprise System, without the disadvantages of a greedy capitalistic system. That takes proper balance, not limiting valid useful products and merchandise.
tovey tovey9 months ago
OH look! I asked a question without using a question mark. I wish I could break that habit.
Actually, considering we were all into serious salmon fishing (Washington State), stainless steel fishing leader was always at hand & might have been the "wire" I remember.
jordanrick1 year ago
Nice! I am cannibalizing the controls from the toaster also- the timer and temp controls are already there, so I am gutting it instead of smashing it [that comes later].
regaltool2 years ago
Pretty awesome make-shift heater. Certainly a different purpose than these heaters, but still nice not to have to spend so much: http://www.regaltool.com/Drum-Heaters-Barrel-Warmers
Just as a thought would this work for bending an arch into a strip of plexi-glass? If anyone has any idea's on how to get a peice of plasic into an arch please tell.
I would imagine it might need a bit of trial and error if you are going to use an standard oven. a temperature of between 140-160 degrees centigrade works best  for rigid foam pvc sheets.
An easier way in DIY situations might be to build a jig or former the required shape, and use a hot air paint stripping gun, applying localised heat and working your plexigalss around the Jig.
You must clamp it in position and allow it to cool completely before removing it, If it is anything like rigid foam it will hold its shape.
Thai plastwood have a series of guides to working with plastic. Check out: www.thai-plastic-wood.com/plastic-uses.html
xeijix (author)  Nunavutnewsrules5 years ago
A while back, I wanted to bend a strip into a parabola, and was trying to think of ways to do it. I saw a video a while back where someone placed a sheet ontop of a parabolic dish and stuck it in the oven. For a strip, perhaps if you taped the ends so that you're adding tension (curves it parabolic like) and place it flat in the oven, that might work.
briskheat5 years ago
BriskHeat offers an inexpensive plastic bending strip heater at

http://www.briskheat.com/p-152-rh-plastic-bending-strip-heater.aspx.

Over 60 years of flexible surface heating experience.
Do you think this could be done using "long" halogen floodlight bulbs as the element? I'm just thinking they give out alot of heat, with the electric safely contained inside a nice glass case. and if done with only a strip exposed as mentioned below you would have a clear indication of where the heat was going as it would be going the same way as the light. I think I may have just thought of my first instructable.
Patented6 years ago
Why am I a colaborator to this instructables?
jueston7 years ago
my tech teacher in highschool had one built something like this, but he had bent sheet metal around it makeing a flat serface so that the heat would rise through a gap in the metal |--   --||   O   |<--- from the side, the O is |_______| is the heater so the heattravels up through the gap and melts whatever is on top just in that little spot so we could bend very acuratelyand all this would take to build is putting 4 bends into some sheet metal and suspending the element somehow
Derin jueston6 years ago
good use of the "pipe"symbol cmon bend that
LanikoAtles6 years ago
EnigmaMax6 years ago
just an idea but, couldn't you use the dimmer already included in the toaster? ( the thing that makes toast dark or light colored.)
xeijix (author)  EnigmaMax6 years ago
Yea, I could've but the way toasters are made, the dimmer device and timer mechanism are cobbled together and it's very weird to work with.
smokehill6 years ago
One method for bending plastic pipe (plumbing-sized) I have never tried, but have had described by a couple of commercial plumbers. Apparently you can soften PVC (up to about 2") by attaching a tube to the exhaust of your truck and letting the exhause heat do the work gradually. My understanding is that they usually have some homemade adapter fitting stuck onto the exhaust, and sometimes they partially block up the "cold" end of the length of pipe, to keep more of the heat inside to soften the material. I don't think this is done every day onsite, but just occasionally when a run of pipes just doesn't quite match up and needs to get a bit skewed to meet another run of pipe.
trebuchet037 years ago
This looks great for vacu forming! Perhaps a little adjustment to the heating element position -- but methinks it could work :D
For vacuum forming, you want an area heater, not a strip heater. For local bends, you want a strip heater.

Check out my article on a small (12 x 20 inch) vacuum forming oven for under $30 using a two-burner hot plate and disposable aluminum pans:

http://www.rcgroups.com/forums/showthread.php?t=621858

brokengun7 years ago
You think this will work for plexiglass too? I recently had an experience trying to working with plexiglass and a bender would come in handy!
xeijix (author)  brokengun7 years ago
Yea, it works. Be a bit careful tho. The plastic bubbles a little when heated and it might show on plexi.
drcrash xeijix7 years ago
The bubbling is due either to heating it too fast, or moisture in the plastic. Acrylics absorb moisture from air (humidity) and when you heat them up, the moisture can turn to steam and make bubbles. If you bake the plastic at 200 for about a half hour per millimeter before thermoforming it, that will drive off the moisture and eliminate the bubbles.
joakimk7 years ago
Cool! Would this also work for bending plexiglass?
Safety concern, tho: Doesn't this mean 110V (or 220, in Europe) will appear across the heating elements, making you, the user, potentionally... toast..? :p
xeijix (author)  joakimk7 years ago
Any thermal plastic. And yea it's pretty dangerous. But then again, so is operating a toaster oven (it's just a stripped down toaster oven minus the timer.)
charper xeijix7 years ago
Solution to safety concern I agree 100% - that's insanely dangerous. You can, however, get an isolation transformer. It doesn't affect the power in any way, it just prevents power from flowing back to ground through you. They're cheap ($30 range) and can be found with a little effort. Realizing that some people may only want to spend $10 to save their life... *ahem* You could go to radio shack and get two identical transformers (make sure they are rated for your toaster's power) and put them back to back. I.E. go from say 120V to 24V and then from 24V back to 120.

Just remember - if you touch the heating element by itself, it'll burn. But if you touch it w/ live power across it, it could kill you - not smart.

Subvert7 years ago
This is a godsend, and so cheap! I think that all thrift stores in existence have at least one toaster oven. What a great and simple idea, and still open to modification. I can now do all the things with plastic that I've been wanting to do for a while now.
i'm so glad you posted this - i've wanted one forever, and knew i'd be better off to build one, but i hadn't gotten around to figuring it out yet.
cylver7 years ago
With a few more pipes, you could make a quick'n'dirty slip roll for making curved shapes and tubes.
ZapWizard7 years ago
Not to offlink, but here is a guide that my friend made for one of these.
http://www.austinpcmods.com/how-to-story--1.html

He sunk the heating element into the wood, which works very well as you can just place the plastic flat on the surface.
cool
jtobako7 years ago
How are you connecting the heating elements, just twisting the leads together or what?
xeijix (author)  jtobako7 years ago
yea, you can't solder them together because the heating elements achieve the temperature where solder melts. You can, however, weld them together
lemonie7 years ago
Are you using the sheet metal as a reflector, heat-shield (for the wood) or both? L
xeijix (author)  lemonie7 years ago
heat shield, and somewhat like a reflector/director. But initially just a shield