Cutting Foam Insulation?

Google "Make A Hot Wire Foam Cutter "

There are some very good websites and you tube videos on how to make one as big as you want for little to nothing.  There is quite a large group of people who make foam air planes that really have made some nice ones that are really big.  Most cost about $20 or so to make.  I am going to make myself a small one.  All you need is some

nichrome wire and a power supply.  One guy made one about 20 inches wide.

D.,

I have a mountain that is 5'X15' completely carved with a 6" steak knife.  At times it was tough sleding but really not all that bad.  I wanted a rocky finish not smooth.  If this is your plan, go with a old knife.  I did have to sharpen it several times.

Paul Edgar

1)  For smooth cuts: I use a 1" break away knife, with the blade fully extended (about 2 1/2") and use the method Tom Tee describes.  (He is correct, you have to get the cutting angle right). I can cut 2" thick foam with no problem, and the method is very clean

2)  For coarse cuts more approrpriate for scenery:  I use a 12" sawzall blade in a holder I bought at Home Depot. The holder makes it easy to use the blade, and the aggresive cut makes it very easy and fast to shape the foam. I have even done four 2" layers at a time. The blade does not care what the glue is between the layers.  It makes surprisingly little dust, and what is made all falls to the ground for easy clean up.

3) I have tried many hot wire cutters. I even made some of my own (see my OGR article on how I made a viaduct from pink foam). I find them to be too difficult to control in long cuts, and the fumes too obnoxious.  I no longer use any of them, even the $200 one. 

I have lived with the mess - the shop vac cleans up the stuff well.    I use an old electric kitchen knife for a lot of major cutting.   For Shaping, I have a "Surform" rasp type tool with a plastic handle.   It is files away the foam pretty rapidly, bu tdoes make a mess - back to shop vac!

I made my own wide-span hot-wire foam cutter. I uncoiled and straightened nichrome heating element wire (salvaged from something) and mounted it in a home-made wood frame with hinge and spring to maintain tension when the wire heats up. I connect it straight across a 12-volt battery (uses about 5 amps I think). I made it originally to neatly cut a large block of flotation foam salvaged from a wrecked dock, to make another seat in a canoe.

On the subject of using large quantities of foam for model railroad scenery, I have to wonder if we shouldn't reconsider more use of plaster scenery for fire safety. Plaster doesn't have to be applied real thick and heavy if you build a suitable lightweight support structure and apply a light coat of plaster first, then build it up gradually. That is what I did on my HO layout. I did use solid styrofoam scenery base on an N-scale layout where the quantity of foam was relatively modest compared to what I see being done in O-gauge.

Thanks for all of the replies guys....this gives me a great start to try several options.....

Personally I use a Sheetrock hole saw. It makes a rough edge. Looks like rock when it's done. Then I use a 3M Sanding Block to smooth it out where I want. The shop vac does the rest. Comes out pretty good.

Good luck with your choice.

Mike R