Cheap ($30+-) and easy to build hot wire foam cutter made from commonly available parts. Cuts styrofoam for surfboards, model plane wings, sculpture, model train or tabletop wargame terrain, 3D sign letters, mold models for lost foam casting, etc.
5/17/2007, Important note! Please be sure to read the comments that other users have left below. There's a LOT of good info there. Check out the links that folks have posted and study what they've said here and you will be able to build a cutter thats suited to your budget and the materials you have access to. There are a lot of alternatives listed or linked below for the frame, the transformer, the wire, the enclosure, and the heat control. Don't underestimate the power of comments! :)
5/17/2007, Important note! Please be sure to read the comments that other users have left below. There's a LOT of good info there. Check out the links that folks have posted and study what they've said here and you will be able to build a cutter thats suited to your budget and the materials you have access to. There are a lot of alternatives listed or linked below for the frame, the transformer, the wire, the enclosure, and the heat control. Don't underestimate the power of comments! :)
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Signing UpStep 1: Parts
The parts should be pretty easy to find.
1. 12 foot, 16 guage extension cord, about $2 at Home Depot
2. 2 wooden yard sticks from the Home Depot paint department, $.97 each
3. 4 #10-24 x 1.25" machine screws with nuts, $1 at Home Depot
4. 10 #10 washers, $1 at Home Depot
5. About 12 feet of strong, low-stretch string. I used 200 lb dacron kite line.
6. A single-pole dimmer switch. About $10 at Home Depot.
7. A 25 volt, 2 amp transformer, $10.49 from Radio Shack.
8. An electric guitar string, about .10 - .16 size. I think around $1? You can get these individually at a music store or you can use either of the 2 smallest strings from a packaged set. You should keep a spare handy because they can burn out or break from too much tension.
9. A length of two conductor electrical wire with a regular plug on the end. I salvaged mine, but you could use another extention cord if you like.
10. A piece of wooden dowel or stiff plastic rod about one foot long (not shown). I used a bamboo skewer.
11. Optional: 4 regular-thickness CD cases. These are for the box that holds the transformer and dimmer switch, but you would be much better off with something like a "project box" from Radio Shack.
1. 12 foot, 16 guage extension cord, about $2 at Home Depot
2. 2 wooden yard sticks from the Home Depot paint department, $.97 each
3. 4 #10-24 x 1.25" machine screws with nuts, $1 at Home Depot
4. 10 #10 washers, $1 at Home Depot
5. About 12 feet of strong, low-stretch string. I used 200 lb dacron kite line.
6. A single-pole dimmer switch. About $10 at Home Depot.
7. A 25 volt, 2 amp transformer, $10.49 from Radio Shack.
8. An electric guitar string, about .10 - .16 size. I think around $1? You can get these individually at a music store or you can use either of the 2 smallest strings from a packaged set. You should keep a spare handy because they can burn out or break from too much tension.
9. A length of two conductor electrical wire with a regular plug on the end. I salvaged mine, but you could use another extention cord if you like.
10. A piece of wooden dowel or stiff plastic rod about one foot long (not shown). I used a bamboo skewer.
11. Optional: 4 regular-thickness CD cases. These are for the box that holds the transformer and dimmer switch, but you would be much better off with something like a "project box" from Radio Shack.
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Any idea what I might be doing wrong?
Thanks in advance.
My problem is that when I cut I have strands of plastic trailing off of the cut edge. Why do I get those?
The resistance of the cutting wire may be so low that the transformer is trying to supply more amps than it's own wire can carry, and so, just like the cutting wire the windings in the transformer heat up/melt.
Transformers are AC devices, they like a nice rounded (sinusoidal) waveform as input. Some cheap (expensive as well as cheap ones) dimmers can output a very square waveform and effectively put pulses of DC into the transformer's coil.
(great for polystyrene) it will run fine even on a 9V pp3 or a bike/car battery... mains adaptors often cant supply the current needed for larger ones but a car charger will do fine. (great if you are out side making adjustments on the fly or your shed doesn't have mains (or a cable that reaches) ... or you just hate people unplugging it when your half way through :D
They also have thermal protection .
The power supply unit I have been using is basically a 12v halogen lighting transformer , these use high frequency (hf) switching to drive a high frequency transformer . they are cheap and light . I wasn't certain how much info you wanted .
I notice that some of the other posters are calling them downlighting transformers .
please read some of the other comments as there are lots .
Since there are 3 output wires. It's will be something like 12-0-12. Meaning that if you use any of the left or right wire with the middle wire, you'll get 12V output, but if you use the two outermost wire only(without the middle wire), you'll get 24V.
A bit confusing, but i hope it helped :)
Forgot to post my email address.
rmndela@yahoo.com.
I have just finished assembling and testing a Hot wire foam cutter.
Works perfectly in cutting large junk styro foam materials into thick slabs or thin slices or into any form.
The power supply is quite sturdy at 6 amperes and has fully-controllable current output to vary the heat of the nichrome wire.
Most of the parts were just salvaged from junk electronics products and few parts were bought from an electronics store. The circuit is easy to assemble for those who could follow instructions.
Please email me if you need further clarifications.
Rod
A Center Tap is a wire that is connected to the transformer winding RIGHT AT the middle. As other commenters have mentioned, when that wire is used in conjunction with one of the other [end of the winding] wires you get PRECISELY ONE HALF [1/2] the voltage, AND if it is wire "like a ground" on two seperate circuits each connected to ONE of the winding "end" wires you get TWO seperate circuits of one half the specficied voltage each.
If you just use the two end wires then you get the full rated voltage.
Again, I'm an electrical/electronics novice, but this is the way it was explained to me. Hope this helps for novices to understand "Center Tapped" transformers.
By the way, transformers can be ordered with several taps [on both the secondary (output) and primary (input) windings to obtain many combinations of voltages and current outputs].
.The only problem I've had is figuring out just the right wire. I used an old #1 e guitar string. But if anyone has any suggestions let me know. I would love to turn this into an automated CNC type system but it's in the drawing phase, and any input will be greatly appreciated. All I have is a regular PC an a free CAD software. Well thank you all and I hope these help(This is not design and I take no credit for it.)
great place to get wire is the local welding supply house. .025 or .030 high
grade stainless steel (316 or 316L) (L is for low carbon) or Inconnel wire
works great. Plus, a good power supply is a small 2 (two) amp battery charger,
or for longer wire operations a 40-200 amp will work.
*A Transformer doesn't require a ground - your work should still be grounded, but not the transformer.