Toxic fumes from foam?

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Well-Known Member
May 10, 2011
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I want to hot-wire some "pink foam" to make a nosecone (I think I know how. I have 2 guides ready, so I figure if I press the hot-wire against those guides, cut the shape, twist the foam a bit and repeat it should work). But my dad says he thinks that it will give off toxic fumes if hot-wired, because of the chemicals in there to keep ants out. I was just wondering if this is true, and if it is, how I am supposed to do this. Thanks guys!

I would think that would happen, but I've never used a wire cutter on foam.

I've just used a hobby knive and just fine.

Makes a big mess but I just keep a shop vacuum handy.

Don't wory about the rough surface, you'll have to coat it with something anyway.

Huh. But that foam is pretty hard to cut with anything.... A hot-wire cutter seems like the best option to me. It also seems a little more exact, I am really not that good at just cutting cones out without a guide or something.
Yes it will give off toxic fumes. Its burning "plastic".
I have never used a hot wire on this type of foam so i dunno if it will work or won't work, but if you do use the hot wire just do it in an open area (well ventilated), away from other chemicals and if possible outdoors.
If you do that you should be fine. BTW dont stand over the work when cutting as the fumes will rise right up your nose :kill:
But that foam is pretty hard to cut with anything....

I use the pink foam a lot to make big nose cones (Carl's HARM missle cone is pink foam under the fiberglass)

Go to an autobody supply and get some 40 grit sandpaper...that'll cut it.

Or get a Starley Sure Form it a raspy type cuter tool. that takes the foam of fast but slow enought that you don't have a chance top make BIG mistakes.

If ya wanna go nuts use a belt saner...but it will make a mess! You'll have platic everywhere.

Stay away from the hot wire cutter...I'm a little concerned about the fumes. You will need all those brain cells some day.

Well, bad news... We just bought a $7 foam cutter. I am going to do it outside, it sounds like it is pretty nasty stuff. if I do it outside on a windy day it cant be any worse than pyrogen, can it?

Unless you made a typo, $7 for a foam cutter isn't all that bad. Remember this - would you rather take the cheap and easy way out, OR get the right tools (in this case, sandpaper and a hobby knife) and spend a little more money and do it the right way?

Personally, I choose a mix of both - I don't try to rush it and make mistakes using the wrong tool, I'll do my best to get the right tool and then if I can't, I'll try it with the wrong tool with the help of my dad or someone that has an idea of what they're doing. PLEASE try to do it the right way!

Jeez... Why is my way always the "wrong way". Whats wrong witha $7 hot wire cutter? it works pretty well, actually, it heats up in a matter of seconds, cools down in a matter of seconds, has a nice on/off switch, and is big enough to make a 3" cone. And I already told you, I stink at shaping cones by hand, I have to have a guide. This is the best way I could come up with, and I am going to give it a shot. Outside, of course. If that doesent work, back to the drawing board.

Where'd you get the $7 foam cutter ? I might want one of those myself.
Michaels. some craft store. I have no idea if it is a chain store or what, so there may or may not be one near you.
What if I had some 40 grit sandpaper on a big sanding block, and I used those forms I just made a day ago? I could just do it the same way I was planning to with the hot-wire, but it wouldent be releasing toxic fumes. Just a ton of dust.....

P.S. Sandman, does pine work well for nosecones? my dad is wondering.....

I sorta make a big emery board with a piece of wood and a sheet of sandpaper glued to it.

You can shape the wood to the curve you want then put the sandpaper on it.

I use contact cement. put the glue on the block and the back of the paper...let it dry...stick it will NOT come off!

Pine is not that good for a nose cone because when it dries it shrinks...a lot!

This is not a problem if you coat it, inside and out, with epoxy. That stuff seals out moisture (or seals it in in this case).

Basswood is better. good luck finding it though...they use it to carve duck decoys. Very stable wood!

Huh. What do you mean, the curve of the cone? you would have to make several hundred sanding blocks, one for each bit of an inch. I am proabably misunderstanding you, but the curve is different for every piece of the cone, is it not? :confused:

Sandman means the block is cut to half the shape of a cone...see the pic I threw together.

<a target="_blank" href="">Nosecone Shaping</a>

Hope that helped,

Not sure about the pink stuff specifically, but using a hot wire cutter for foam is a perfectly acceptable method. It is exactly the right tool for the job, particularly for forms that can't just be turned on a lathe. Airplane guys use it to shape airfoils all the time.

Do a search on Google on airfoil construction or hot wire cutters for R/C planes and you should find a wealth of information. I believe there is even an article on ROL's InfoCentral on the topic, but I'm too lazy at the moment to look.

Hot-wire cutting is the standard method of forming polystyrene foam into the desired shape. Pink, blue, and white foam from hardware stores is all EPS (expanded polystyrene.) The list of things they make is endless: so a Google search for 'hot wire foam cutting' to find lots of information. There is an annoying odor, but I don't believe that the fumes are toxic. Of course, you should use adequate ventilation anyway. Here's some good links regarding it. Note that the Team Vatsaas folks have made some great rockets this way. wire foam cutting.shtml

IMPORTANT NOTE: Hot wire cutting should not be used on polyurethane foam (the yellow stuff, or the stuff from the cans.) This foam DOES give off toxic fumes (after all, its made from urea and formaldehyde.;( ) Manufaturers may use hot wire cutting for polyurethane, but it's just not worth it for hobby use.

Mark E. Hamilton
What about sanding polyurethane foam? Would that work?

Sanding polyurethane works (at least, it doesn't release toxic fumes.) However, I've had problems with it crumbling more severely than polystyrene. Some sands better than others. Also, one of the nice thing about polystyrene is that you can buy it in 4x8 sheets, in a number of thicknesses, and any home improvement store (Lowes, Home Depot, etc.) I can't say the same for polyurethane.

Mark E. Hamilton