Cutting Styrofoam?

Instead of a hot wire foam cutter which is to expensive. Does anyone have any tips on cutting this stuff?

I don't know what you call to expensive the cutter that I use cost about $20.00 I use a Radio Shack 110 volt to 12-24 volt transformer some 1X2 wood and a piece of aluminium 1.5" angle and nicrome wire from Sig Mfg and I cut over fifty sets of foam wings and it still works fine.

Stainless wire is cheaper than nichrome. It works better,too. You can use a piece of flying line. That's pretty cheap. You can get a lot of it free by hanging around a combat contest.

Howard, what kind of wire you tried? Only stainless?

I am sking because we got lot roubles using carbon steal wire (not stainless) with stability of temperature. Especially cutting small parts (elevator) by long wire (for wing). It looked like overheating out of foam and cooling in foam. Since we used wire with better thermal stability of resistance it is much better. It looks like (my guess) the part in foam cools down, loses its resistance and thus can not heat back, while part out of foam is heating, getting resistance and not allowing higer current for that part inside. Is it better with stainless wire? If yes, it can be used at higher tension I think.

I had not considered the resistance variation with temperature, but that would be important. I use single-strand stainless because it takes higher tension than nichrome. The high-temperature strength of nichrome is unnecessary, because the wire doesn't get very hot. I shall look for a material with less resistance variation with temperature.

The resistence variation is not problem if the temperature is uniform on whole length - as it cools down it gets higher current, but if you cut by only fraction of length ...

And what thicknes you use? I think I have 0.4mm wire - we use only 0.3mm and .4 looks too thick for me, but in message lower Brett writes he has goot experience also with such thick wire. I think I will try it.

>The resistence variation is not problem if the temperature
>is uniform on whole length - as it cools down it gets higher
>current, but if you cut by only fraction of length ...
>
>And what thicknes you use? I think I have 0.4mm wire - we
>use only 0.3mm and .4 looks too thick for me, but in message
>lower Brett writes he has goot experience also with such
>thick wire. I think I will try it.

Make sure you have a fuse in the circuit. If goes almost without saying that the current goes up at the wire diameter goes up. Mine draws something like 3.5 amps at 12v.

I see, thicker low resistance wire will need less voltage and more current. We actually use 0.3mm at 25-30V and only 1.5A. So it looks I will need definitelly different power supply. But charger for automotive battery will help I think

>I see, thicker low resistance wire will need less voltage
>and more current. We actually use 0.3mm at 25-30V and only
>1.5A. So it looks I will need definitelly different power
>supply. But charger for automotive battery will help I think
>

That's what I use. I have a Variac (heavy-duty variable transformer) on the input side of the charger. You could use the Variac directly, but they are auto-transformers and if you get the plug flipped over, it puts the "hot" side of the voltage on the wire, and then you get electrocuted. I'm not sure how European 240 works - I would guess two hots 180 out of phase and a ground, but the car battery charger should provide any isolation you might need.

We have 220V it is relatively danger and so our norms does not allow any auto transformers, but charger giving some 15 volts for lead batteries is not a problem.

.4mm (.016"). The resistance problem appears when cutting a wing with a high taper ratio. I pass air through the foam near the tip LE to keep it from melting too much.

>.4mm (.016"). The resistance problem appears when cutting a
>wing with a high taper ratio. I pass air through the foam
>near the tip LE to keep it from melting too much.

LOL Howard I would really like to see a picture of that!

It's merely a table with holes in it with a box underneath up to which I hook a vacuum cleaner: an HVLP vacuum clamp. It holds the foam block in place nicely. Just put extra holes in the table near the tip end and near the LE.

Yeah, I must admit, I chuckled when I read that. Trust Howard to think of something like this.

I use a "bed of nails" for my foam cutting. The holes in the foam don't hurt it. I also use half-templates, so I don't need to draw center lines, or anything like that..

>>.4mm (.016"). The resistance problem appears when cutting a
>>wing with a high taper ratio. I pass air through the foam
>>near the tip LE to keep it from melting too much.
>
>LOL Howard I would really like to see a picture of that!

You got a dirty mind , brother John. (if you don't know what I'm tlakin' about, then I am the dirty minded character!)

God bless you!

In Jesus,

>I am asking because we got lot troubles using carbon steal
>wire (not stainless) with stability of temperature.
>Especially cutting small parts (elevator) by long wire (for
>wing). It looked like overheating out of foam and cooling in
>foam. Since we used wire with better thermal stability of
>resistance it is much better. It looks like (my guess) the
>part in foam cools down, loses its resistance and thus can
>not heat back, while part out of foam is heating, getting
>resistance and not allowing higer current for that part
>inside.

That seems like a good guess.
I would apply power just at the point where the wire enters and
exits the foam, minimizing the length of the wire not in the foam.
Easy to do with little alligator clips.

>Stainless wire is cheaper than nichrome. It works
>better,too. You can use a piece of flying line. That's
>pretty cheap. You can get a lot of it free by hanging
>around a combat contest.

Plain old music wire straight out of the K&S display also works just fine. I think I have used anything from .012 to .018 with good results.

You can't get much cheaper than Carl's $20 setup. It will probably take some fiddling with wire diameter and length to get the right temperature. Jut remember Ohm's law- V=I*R Voltage drop across the wire equals the current times the resistance. And power- W=V*A watts (or the power heating the wire) equals volts times amps. A smaller diameter or longer wire has more resistance and needs more voltage to keep a given temperature. Shortening the wire and/or making it thicker will increase the amps and the temperature. Just make darn sure you setup can't put full line voltage on either end of the wire. An isolation transformer is a must.

Speaking from years of experience, the wire must move at a very steady speed.

The correct temperature depends on the foam. when thewire is just right, and the speed is just right, the wire will bow or drag back in the middle of the cut slightly(1/4-3/8 in. on a 30 in cutting wire). Cutting by hand you won't feel any drag from the wire.

Make bows with different length for different jobs. It is very difficult to make a cut using the center 2 ft. of an 8 ft cutting wire.

Almost any wire will work for the bow if you find the right temperature, tension, and cutting speed. The biggest difference is that plain steel music wire will corrode quite quickly. Stainless lasts much longer. Nichrome lasts pretty well but is weak and prone to breakage.

>Almost any wire will work for the bow if you find the right
>temperature, tension, and cutting speed. The biggest
>difference is that plain steel music wire will corrode quite
>quickly. Stainless lasts much longer. Nichrome lasts
>pretty well but is weak and prone to breakage.

It is also helpful to tension the wire with a small spring at one end. Easily available from Home Depot. I have built a small hot wire "table saw" that cuts small parts just like a band saw. Spacemodels (rockets) often require small foam parts, hence the saw. If there is sufficient interest, I can post some pix. In my "Snorky" thread, I obtained a good source of pre-cut generic foam cores. But it sounds like you guys are having so much fun, maybe I should try to cut my own, just for the heck of it (valuable skill learned).

In any event, don't be afraid of hot wires, they are easy. Electric train transformers can be used as a power source too.

Ferocious is the master of foam cutting. He is proprietor of the Core House, which has been computer-cutting foam wings for decades.

>Ferocious is the master of foam cutting. He is proprietor
>of the Core House, which has been computer-cutting foam
>wings for decades.

Howard,

Ha yup! He'll probably get some of my business in the future too. My comments (like Phil's) were directed to those who had *never* worked with a hot wire. I sure don't expect to tell Phil how to cut foam!

I didn't mean to imply that you were disputing Phil. I just wanted to blow his cover of modesty.

How do you measure the heat of the wire?
Could you use a laser pyrometer?
Sure would like to see a line drawing of this type set up.
I would just like to do a few body molds.
Remember ; I was run over by a cart, pulled by a blind mule ,
as a child and need help.

Thanks

A huge band saw with a 30" throat??? Naw, go with the hot wire.

Ferocious is the master of foam cutting. He is proprietor of the Core House, which has been computer-cutting foam wings for decades.

Howard,

While I agree with your statement above, one does wonder if even Phil has fiddled with *tapered* wire used to cut foam?

Care to add to that comment?

That will be enough out of you.

>Ferocious is the master of foam cutting. He is proprietor of
>the Core House, which has been computer-cutting foam wings
>for decades.
>
>
>Howard,
>
>While I agree with your statement above, one does wonder if
>even Phil has fiddled with *tapered* wire used to cut foam?
>
>Care to add to that comment?
>
>
>Dan

Ron B.
F4Fguy

I have.

The cutting bow itself need not cost more than a dollar or two, honest! Find a piece of 1x2 lumber about 4 feet long, some nails, one 1/4" bolt (about 2 1/2" long) and matching nut, one cheap guitar string (steel), and you're all set.

Power supply? Yeah, that'll cost you maybe $20.

Heck..a surform tool cost nearly as much as a hot wire set-up. Any other method makes an incredible mess.

>Ferocious is the master of foam cutting. He is proprietor of
>the Core House, which has been computer-cutting foam wings
>for decades.
>
>
>Howard,
>
>While I agree with your statement above, one does wonder if
>even Phil has fiddled with *tapered* wire used to cut foam?
>
>Care to add to that comment?
>
>
>Dan
Ron B.
F4Fguy

I have.

Ron B.

Howard shut me down.

Phil hasn't taken the bait.

Ron says he has done so.

Francis doesn't appear to be involved with this site.

So I know three people who have actually cut foam with a tapered wire.

Hardly a movement afoot here, we will leave one and all to ponder the mysteries.

It seemed a way to make the wire really weak. I spent a day trying to taper wire and then pull it tight enough to cut foam. It did give Dan a chuckle, but nothing more came of it.

Build a spool-like arrangement on each end, and move the wire
sideways while cutting, from root towards the tip.
That way, "fresh" hot wire moves into the foam, cutting faster,
while the "used" colder wire moves towards the tip, cutting slower.

Very cool idea. Maybe you could modify a bandsaw to do this. You could either circulate the wire, in which case you'd have to weld it nicely, or start with a lot of it and just wind it up as you go. 10 feet ought to do it.

How would you keep jive from building up on the tip template?

>How would you keep jive from building up on the tip template?

Not sure. Maybe you don't: Since the wire is moving along the
template at the same time, the jive should end up evenly distributed
around the template.

But I would think that we'd want the wire clean
and smooth where it hits the template, so maybe a wiper is required.

Maybe if it's hot when it hits the template, it won't matter?
Experiments required, I guess.

Ron B.
F4Fguy

I only said I did it.I didn't say I liked it!

Seriously though,it was a lot of trouble for little improvement.I started with some 0.035 stainless MIG wire and finally got a reasonably even taper to 0.025 in about four feet.Frankly,I couldn't see any real difference(that I could ascribe to the taper).Strength wasn't a problem,but then my setup is somewhat different than most.
I use a single point system for most of my cutting since most of the parts are tapered.The wire is tensioned by pulling it with a cable through a pulley and weight at the pivot end,so tension is constant as long as the weight is off the floor.Current is only applied to the wire actually in the cut(plus a little*).
*I've found I get a smoother cut by occilating the wire about 1/2" as I cut.
Apparently I cut at somewhat higher wire temp than most,as I seldom see more than 1/16"-1/8" "drag" in the center.As an indicator I raise temp until I get a lot(scientific term)of "strings" on the cut surface.
Almost forgot!after satisfying myself that tapered wire wasn't worth the trouble,I found I could get pretty accurate and constant taper by taking a wire several times longer than needed,putting it under tension,and applying enough current to yield it.This gives two lengths of almost perfectly tapered wire.

I use big rubber bands for tension, even though I bought one of those "guitar things" that Loet Wakkerman shows on his web site. And I use a LOT of tension and a hot wire, as well. I, too, don't think that there's more that 1/16" drag when I do my cuts.

>I use big rubber bands for tension, even though I bought one
>of those "guitar things" that Loet Wakkerman shows on his
>web site. And I use a LOT of tension and a hot wire, as
>well. I, too, don't think that there's more that 1/16" drag
>when I do my cuts.

Ron B.
F4Fguy

The trouble with rubber bands,springs,heavy music wire legs,etc,is that they all have varying tension with varying wire length(like when it's hot).To compensate you have to use very high cold tension,which unnecessarily stresses the wire.The weighted tension is constant,hot or cold.

True, but my wires don't expand much, if at all, when hot, and I use one bow for most things, so the length doesn't change except what's due to expansion. I quit breaking wires when I switched away from nichrome.

My setup is incredibly cheap, compact and easy to make, and it's fine for Combat wings. Don't know if I'd use it to cut glider wings, though, those have very precise airfoils and very thin trailing edges. Similarly, if I were to cut Stunt wings I'd probably have to incorporate some sort of quick-release quick-attach linkage for the wire so I could pull the wire through pilot holes in the core to cut out the hollow parts and using rubber bands for tension would be a hindrance.