Cutting foam with hot wire

[KARKAUAI]

Aloha, everybody,
I'm starting to think about the next part of my Hawaiian outrigger...building the amas. I'm going to build them out of closed cell Styrofoam with a center plywood support. Dreading the thought of all the foam chips/dust. I've heard of cutting foam with a hot wire but haven't found anybody who's got specific plans for making up my own cutter. I've heard that I can use a battery charger to supply current, but don't know about what kind of wire, or how long I can make it...the blocks I'm using are 21 inches high by 12 inches thick. Anybody ever done this on a large scale like this? Anybody have specifics about how to build the cutter and tricks of the trade?
Mahalo, Kent

[Chris Ostlind]

You won't need to set up a hot wire to cut your foam.

For lots of foams you can use a Surform tool. http://www.stanleytools.com/default.asp ... AND+BLADES They come in a variety of styles including rasps, block planes and jack planes. There is also a product called Microplane http://www.microplane.com/html/index.html that works very much like a Surform except it has a smaller bite into the material and delivers a smoother finish.

Another tool that is really handy for doing heavy shaping of foam before the above mentioned rasps/planes is a good old, electric, dual blade reciprocating turkey knife that your parents probably quit using to carve the turkey many years ago.

I've shaped lots of foam amas in this fashion and the work is quick and yields a pretty nice, shaped form that is ready to glass.

Recently I've been using the blue foam that is used in the construction industry for insulation board. I buy the 2" stuff and glue panels together with slightly thickened epoxy to create laminate thickness prior to carving and shaping.

If you want to go whole hog, you can make a generic form out of cardboard that is larger than the ama will be when finished, get a couple of gallons of two part urethane, mix up a batch and pour it into the form. It will cure quickly and shape easily to a final ama form for glassing.

Both of these foam types are compatible with epoxy and will get you a very quick, very strong ama so that you can experiment with a variety of shapes and displacements for your project.

Have at it.

Chris

[KARKAUAI]

Thanks, Chris,
I've got all the tools for hand shaping. What I'd like to avoid is the chips and foam dust that I can only imagine will be EVERYWHERE if I use rasps, etc. I was hoping to do the major cuts with a hot wire, and do the final shaping with the hand tools.
What kind of canoes do you build? Kent

[Dean in Eureka, CA]

Hey Kent,
Are there any surf board builders in your area? I would talk to those guys. I've seen a local builder rough his shape out with an electric turkey carving knife, then final shape them with suforms.

[KARKAUAI]

Hey, Dean,
No surfboarders here, remember, I'm building this canoe in NC foothills. Turkey knife sounds interesting, though. I've got a contact in Kauai who builds boards, though, I'll contact him. Mahalo, Kent

[KARKAUAI]

Well, from everything I've learned from the internet and a surfboard builder, the hot wire cutter sounds like it'd work great. Unfortunately, the variables of wire size, different foams, power source, etc. would require a lot of experimentation. I decided to just go with a saw and hand shaping tools and clean up the mess. Thanks all. Kent

[Todd Bradshaw]

A small hotwire system would certainly eliminate a fair amount of the foam dust, but it might take a week or two to get one or find the parts needed to build one. There is a small production model made by Woodland Scenics, a company that makes scenery materials and tools for model railroading and which is retailed by the big mail-order suppliers. You can see one about half-way down this web page.
http://www.nscalesupply.com/Wsc/WSC-Tools.html
I have one and plan on using it for the rough shaping when I finally get around to building my Ulua. It's not a very heavy-duty tool and it's not a really precise tool to use, but will do the job for cleanly knocking the corners off the block and cutting down closer to the final shape - at least close enough to eliminate much of the surform time.

There also are instructions on the web for building larger, stronger (and cheaper) units. Some do use a battery charger, but the better ones often use old model train transformers, like this one, which is one of the best I've seen.
http://vatsaas.org/rtv/construction/hotwirecutter.aspx

The old Marx transformers show up all the time on eBay in the $5-$10 range. Newer transformers don't work well because you're essentially "crossing the wires" to get the thing to heat up your foam cutter and new models have built-in circuit breakers that shut the thing off if you short-circuit it. I suppose the same PVC pipe frame would also work with a battery charger for power, but I think I'd read a bit on wiring my battery charger to it before trying it. Whether you use a hotwire for this boat or not, they are neat tools, easy and cheap to build and worth having to play with.

[KARKAUAI]

Mahalo, Todd, That's exactly what I was looking for...I'm going to look around for a transformer and give it a try.

[Jeff in Farmington, MI]

I built a similar foam cutter to shape sections of foam for a model train layout (mountain building). Since I had trains on my brain, it was natural that I'd use an old train power transformer as the power supply for the foam cutter. It was very simple, cheap, effective, and totally avoided the nasty pieces of foam that result from cutting tools.
A five foot nichrome wire can be purchased for a couple dollars at a hobby store that sells model airplanes and parts. Construct an H-shaped frame in any size you like from three scrap pieces of wood. Use a single bolt (loose) where the pieces join so that they can pivot. Attach the wire with bolts near the ends of two legs. Use a bungee cord across the opposite ends to keep the wire taut.
Attach insulated wire leads from the wire bolts to the transformer. The transformer is great because you can crank up the power for thick pieces, but keep it low for thin pieces. You can clamp the bow in a verticle position on a table and use it like a band saw.