Hot-wire cutting foam for aero-mods

[Varn]

Yeah just grab one of your old spools. Not sure how the wire would work if it hollow core flux filled glowing hot. Just try it. Steel wire is better than copper. Higher strength.

My charger is my small old one. about 30 years old. I converted it to a full wave bridge after the half wave system burned out.

If your already have a decent powersupply Then go for it, whatever works. One thing that I don't like about your powersupply is that it is basically 120 volts that are pulsed. So be careful about electrocution hazard. I like the idea of a transformer to isolate me from the wall voltage.

I would like to make a couple of plywood patterns and make a foam nose for my vw.

[bennelson]

I was just playing around, trying it out. I don't think 120V AC for a final design would be a good idea either.

A battery charger as a power supply sounds like a good way to go, because it already has a transformer in it to lower the voltage, and is something a person is already likely to have.

[dcb]

Originally Posted by Varn

...I converted it to a full wave bridge after the half wave system burned out...

In case it isn't obvious, rectification is not needed in this application. I've done the dimmer->xformer wire cutter too, works just fine for my purposes. Start on low power and work your way up so you don't fry your dimmer.

[Varn]

Yes good point, of course AC would work as well. But I didn't have a convenient AC power transformer hooked up but did have a battery charger. The reason that I pointed out that mine was now full wave is because it improves the average current flow. You know hump hump hump vs hump space hump space.

Please consider that if you are using a dimmer, it would work fine except for safety, there is 120 volts available to shock you. The way that I understand dimmers is that they basically limit the duty cycle so that you are getting just part of the waveforms. I originally was going to use a dimmer but thought that I would try the battery charger first.

I used to have a battery charger that I made using a light bulb and a rectifier. I mounted them in series. It worked to charge my storage battery but there was always the potential for putting the hot side on the ground making it dangerous. You could lean against the car and if you were touch ground it would shock.

Originally Posted by dcb

In case it isn't obvious, rectification is not needed in this application. I've done the dimmer->xformer wire cutter too, works just fine for my purposes. Start on low power and work your way up so you don't fry your dimmer.

[Otto]

Electric train transformer or dimmer switch + nichrome wire from model airplane shop or stainless steel guitar string + bow made from fishing pole or thin dowel rod = works pretty good

Some folks use cheapo Chinese soldering gun + bent to shape copper wire, for foam extrusions or sculpting

[dcb]

My new hero in the resistance heating category is Jack Bauer FYI:
Honda CBR600F2 conversion

[JasonG]

I have a friend that does cast concrete/cochina (sp?) stone.
He powers his frame cutter from a transformer and dimmer switch.
Said he would get shocked with the 120V unit.
About a 4" spring on the frame keeps it tight.
He uses masonite board for the profile shape and runs the wire along it.
He has 24" and 48" frames, I have always wondered if for a vehicle this would work:
Use a dowel on each end of an 6-8' piece of wire.
Have one person hold each end.
Guy in front follows old body.
Guy in rear follows end of boat tail shape.
Done in no time

[winkosmosis]

Do it outside so you don't inhale the fumes

[shorttimer]

I think stainless wire would be the ticket. But i would check with people who sell the equipment for hot wire cutting first, just to make sure.

[Otto]

Originally Posted by JasonG

I have a friend that does cast concrete/cochina (sp?) stone.
He powers his frame cutter from a transformer and dimmer switch.
Said he would get shocked with the 120V unit.
About a 4" spring on the frame keeps it tight.
He uses masonite board for the profile shape and runs the wire along it.
He has 24" and 48" frames, I have always wondered if for a vehicle this would work:
Use a dowel on each end of an 6-8' piece of wire.
Have one person hold each end.
Guy in front follows old body.
Guy in rear follows end of boat tail shape.
Done in no time

Homebuilt airplane guys have done this for decades, for wing airfoil core profiles, which are critical in exact shape.

Due to wire lag, cut no more than ~4' sections, otherwise the wire lag makes scallops in the foam. Don't rush it--let the heated wire do the cutting at its own pace b/c if you pull it will stretch or break the wire. Slower and at wire temperature just hot enough to cut makes a better cut.

Another non-hotwire prospect is to just use polyurethane foam, placed on a frame of the correct template shape, and simply sand or cheese grate the foam to shape. Makes a lot of powder that goes everywhere, but those who've worked with styrofoam and polyurethane say poly is the only way to go. Poly lets you use cheap poly resin, vs. much more expensive epoxy, and is more chemically compatible. A couple of 4'X8' 1/2" sheets from Lowes or Home Depot would do the trick. Peel the aluminum foil backing off. For compound curves, score the back side of the foam so it will more readily bend. Face both sides with light fiberglass cloth for a light, strong sandwich structure.