Wite for foam wing cutter

Now that is interesting "The Source". I had a feeling the shack is fading due to an inventory makeover . Hardly any nuts and bolts left. Mostly appliances.

I agree with Jim. The shacks around here are crap. They never seem to have anything I need. RC, HAM, Science Fair Projects...

You can go to the trouble to find nichrome wire, or much easier, just use stainless steel aircraft safety wire, .020 diameter for small jobs, .032 for longer sections. Check with a mechanic or supply shop at the nearest airport. Usually you gotta buy a pound at a time, which would last you several lifetimes of foam cutting,at about 7 or 8 bucks or so. A mechanic might give you some for free. You see, A/C safety wire is the stainless with a high melting point, and (without taking the time to actually look it up) I suspect is actually very close to nichrome, if not exactly what Sig and others sell as nichrome. After all, the two major alloying elements of stainless steel are none other than nickel and chromium. The name Nichrome is applied to several different alloys, incidentally. The two common stainless steel types are known as 300 and 400 series; one's hi temp, the other is better in salt water. I just did a job where we had to cut 4' blocks of foam rubber, and .032 safety wire and a 15 amp variac did an admirable job. Good luck- It ain't that difficult- Paul

I would like to agree with what Paul said, and add a slight bit to it. Before I retired from the DuPont company, we bought considerable amounts of small diameter stainless steel wire for use in one of our processes. I recall it was about 10 mils in diameter (same as .010 inch). Whenever I needed a small amount for foam cutting, I'd salvage a few feet from a failed unit in our process and bring it home. Using a Variac or Powerstat, feeding through an isolation transformer, did the job. The isolation transformer is desired to avoid getting shocked from the output of the Variac hooked directly to the 115 v. line, and then to the wire.

Later on in life, at a Ham Fest in Charlotte, NC I bought from the flea market a 1 pound spool of another type wire, which works for me just as well as Nichrome or stainless. It had the name of Tophet A alloy on it, and was made by Carpenter Technology Corp. It was 5 mils in diameter, and marked wire size 36. More important, its label says

25.24 ohms/foot of length. In my tests with this wire, I found it works best at approx. 16 watts/foot, which works out to 0.8 amps of current. So for a 30 inch length, it needs approx. 50 volts ac. Other lengths require voltages in proportion to this. After doing an extensive search on Google, I found Tophet A is the same exact alloy as Nichrome V - just in case anyone asks. Which is 80% Nickel and 20% Chromium. It does elongate slightly upon heating, so some sort of tensioning spring is advised in your cutting "bow" or device.

Maybe this will help, sorry it got MORE than a slight addition.

Olin

If you have a fishing supply around you, look for stainless leader in diameters between .016 to .025. Smaller wires for shorter cutters (less than 30"). You will need a bigger transformer as stainless requires higher voltges than nichrome to heat. I use a 24v, 5a filament transformer going through a bridge rectifier and some 33000uF capacitors in parallel. This gives me a powerful 35v source. Works well for wires up to 54" in lengh on my computerized cutter. My computer also controlls the heat by varying the duty cycle of the supply.

An ammeter has to be in series with the load to measure current. Don't bother if the multimeter hasn't got an AC Amps scale; many don't and a DC ammeter won't measure AC. We've cut foam using .020" aircraft stainless safety wire and a 12 volt car battery. A battery charger will work, too, but it needs to be a 10-amp or better to avoid a large voltage drop when driving a cutting wire; the voltage drop causes an amperage drop, too, and the wire won't heat enough. We found that a 30" chunk of the .020" wire drew about 2 or 3 amps.

Dan

Hello,

I once tried to build a foam cutter. And in doing so I nearly go myself killed.

I bought a new Newstar adapter/charger which was rated output, D

12v/8a, 24v/4a. I could not find any nicrom wire so I just took som length of wire and attached it across the 24inches 'H' rig I build.

Attached some length of wire to the opposite ends of the bare wire o the 'H' rig and the other end to the respective + & - terminal on th adapter/charger.

Happily, I turned on the power and there was a loud bang and the whol house went dark. The main's CB triped and the adapter was burnt.

I later found out from an electronic technician what I could hav killed myself with the contraption I build. Apparently by using wir instead of nicrome I basically created a short-circuit across th adapter/charger terminals. Nicrome wire works because it has resistance across the wire.

Are you sure you can use fishing wire?? Some one told me guitre wir can be used as substitute to nicome wire but I dare not try any more. Just in case I run out of luck and lives.

I thought DC was safer to work with. I cannot imagine what would hav happened if i had the contraption on AC.

Cheers

-- shi

----------------------------------------------------------------------- shim's Profile:

this thread:

I think killed is a little overstated. From a technical point of view, using copper wire with a very high conductivity is incorrect, as you want the wire to be a resistance and heat up, but it is very hard to see how you could have killed yourself - you were dealing with low voltages with an unmodified, commercial product. My only concern is that it seems the charger did not have its own fuse, rather relying on the circuit breaker.

Thanks for the input, all!

I'm going to have to do some checking around at the local aviation service shop (Buttonville Airport in Markham, Ontario) or the Big Bass Pro Shop in Vaughan, as well as the local Home Depot.

I've also got some leads on how to set up a rig like a vertical band-saw plus one for vertical cuts. Problem right now is that I can't get two sets of core-cuts to match, and the supply of 2-inch foam in the area is a bit limited, so every piece counts.

For those in Canada, have a good Domini.... uh CANADA Day, and those a bit further south, have a Fantastic Fourth!

Can anyone point me at a website that describes how to build a hot wire cutter for foam?

Thanks

On Sun, 25 Sep 2005 21:00:20 -0500, "H Davis" wrote in :

Here's a power supply:

Marty

Thanks Marty,

Nice looking Power supply.

Thanks, Marty! Its good to know that something like this can be built, but I really suck at electronics. I'd need someone to "hold my hand" when I even tried to build this power supply?

Do you know of anyone who sells these power supplies for $75 or so?

Harlan

On Tue, 27 Sep 2005 00:13:45 -0500, "H Davis" wrote in :

No, I don't.

I bought my foam-cutting gear from Feathercut. It's good stuff, but pricey. I figure if I build four or five planes with it, the investment will pay off.

Marty

How about this?

I haven't tried it, but if I ever get to cutting foam, I've got my eye on it.

PRose

I have a computerized cutter that can handle cores up to 50" long with an

18" chord and 12" height. I can cut just about any shape you can draw.

I just moved from the UK so I am not set up yet.

Cutting foam is not rocket science. I use a simple 36" bow made from .012 control line flying wire and the power source is a 12 volt auto battery charger. I have cut hundreds of foam wings for control line combat planes. If you want more info drop me a line at snipped-for-privacy@aol.com it really is easier than you think.

Bob Furr "See ya in the circle!"

Cutting foam CAN be rocket science if you want to go beyond simple CL combat designs. I have a computerized cutter that can cut cores of 50" span and

18" chord. Can cut any combination of root and tip airfoils from a simple drawing.