Man I wish I could hang onto a train of thought. A couple of more bits of info.
When attaching your power supply wires to your cutting wire, you need to use alligator clips( that's how I do it ) or clamps. It can't be soldered because to cut foam cleanly you're wire temp has to be between 600 and 800 degrees, the same temps that solder melts at.
I tried the radio shack setup, the old battery charger setup....they somewhat work, but nothing like the setup I built from jacob's online. The transformers they sell are designed for this type of use. Also, if you buy your transformer there, buy it with the dimmer switch they sell. Works perfectly.
Foam.
The best foam for being hot wired is EPS ( white, beer cooler foam). It cuts cleanly at reasonable temps and gets a nice hard skin on it after it's cut. For wing cores this is what I'm using. You can use the blue or pink, but the quality of these foams has gone down. There can be outside debris trapped inside it that won't cut with the hot wire and it will drag through the foam as you're cutting leaving grooves and imperfections. This can be overcome during finishing, but who wants the extra work.
Finishing.
All of the foams available to us for hot wiring need protection after assembly. I've tried a number of techniques, from silkspan, brown paper, news paper, coffee filters, fiberglass and epoxy, fiberglass and water based poly urethane, fiberglass and urethane, balsa sheeting and liquid sheeting.
My personal preference is to use fiberglass and w.b.p.u. . On planes under 48" wingspan I use 1/4 oz. cloth, 48" to 60 " I use 1/2" cloth and epoxy, bigger than 60" will require multiple layers of 1/2 oz. cloth ( you could use heavier cloth, but the 1/2 oz. conforms to curves and radius's nicely) and epoxy or sheet with balsa first, then one layer of 1/2 oz. with epoxy.
On smaller planes, you can fill the weave in the cloth with additional coats of w.b.p.u., sanding lightly between coats.48" and up, I like to fill the weave with a mixture of light weight spackle, Durhams rock hard putty, baby powder and water. The baby powder makes it very easy to sand and keeps from clogging the sand paper. Mix equal parts of light weight spackle and durhams , about half a part of baby powder, add water until it's a pasty consistency with no lumps. You want it so you can just rub it on by hand ( in a rubber glove) and try to keep it smooth for less sanding. It's going to feel like it's added a lot of weight initially. Let it dry over night and you'll see it's much lighter once the water has evaporated, and it will get even lighter once you sand most of it off( you don't want to sand through the fiberglass, just until you can barely see the weave). Once you've reached that point, you can mix up another batch, this time with equal parts spackle/durhams/baby powder and mix it a little wetter so it can be brushed. coat the whole plane, let it dry for 24 hours and sand it smooth with first 220 grit, then finish it off with 400 grit. should be glass smooth with a hard finish and be ready for liquid sheeting ( which should need no sanding if it's applied right) or just paint it( on large planes I like the liquid sheeting before paint).
I've subscribed to this thread, so if you've got any questions just post them and I'll try to help.
Bill
