Bob;
The hot wire cutter was particularly easy to make, I knocked it out in a
short afternoon after becoming particularly frustrated at getting smooth cuts
with carving knives and "hack" saws.
For the cutting element I used some .032 SS safety wire that all good
aircraft people have laying about. I pounded 2 large nails into a length of
1" X 2" board to span the wire with, make it taught and secure, though it
will expand and loosen when heated. I used a 12 battery charger for motive
power. Those trickle chargers won't work. My charger has an amp meter on it
and it seems to work best when drawing around 5- 6 amps. My cutter is short
only about 10" long so you might want some extra amperage if you are going to
ger creative.
To vary the load to optimize cutting I took another board and pounded in some
more nails to zig zag some more safety wire across. One lead from your
cutting wire goes to a nail on this board that is hooked to one lead on your
power supply. The other lead from your cutting wire is attached to one of
nails where the safety wire is zigged zagged across. The only thing now left
in your hand is the other lead to the power supply. This item gets clipped
at an arbitrary position away from where the lead from cutting wire is
attached to zig zag wires. If everything starts glowing or your trip your
charger its too close. Use the safety wire only for the cutting and the
resistance adjuster wires. Use some good heavy gauge insulsated wire to
connect the cutter to the adjuster for low resistence (16 ga or heavier)
To optimize foam cuttingfrom Rutan's book:
"Adjust te current to obtain a wire temp to allow the wire to cut at a rate
of about an inch every 4 seconds when pulled with a light load (less than 1/2
lb.) Correct temp will give the foam smooth hairy surface. A cratered
surface means too much heat. If the wire is too cold the cutter will have to
be forced hard causing the wire to lag."
This came out of Moldless Composite Homebuilt Sandwich Aircraft Constrruction
3rd ed. 1983.
Steve Hagar
A143
Mesa, AZ
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