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| June 1, 2002. I made the hotwire templates to cut the foam pieces to a
consistent size. They are made of MDF that I had laying around. They worked really well as cutting guides. |
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| The hotwire cutter was made from stuff I purchased from Lowe's. It is aluminum U channel with 3/4" wood stiffeners. The tension is provides by a screen door spring and a turnbuckle. The wire is.020 SS safety wire. I also have a roll of nichrome wire but have not used it yet as the SS wire does fine. I use an isolated
Variac transformer to provide the current to the hotwire cutter. The 7' hotwire cutter seems to need about 35V to work (I do not know the
actual current but it is about 2-3 A). It takes three to make the cuts. Two to control the cutter and one to control the
Variac as needed. |
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| Here is one of the stern pieces with the guides mounted. |
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| Another picture of a hot wire guide mounted on the other end
of the foam. |
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| June 8, 2002. This is a picture of the hotwire
bow to cut the lift duct hole in the hull. The bottom cross wood dowel
is attached to the 3/4 aluminum tube once the tube is through the center
hole drilled in the foam hull. A slot also needs to be cut in the foam
hull to allow the hotwire to be strung between the two dowel rods before
actually turning on the current and making the cut. Worked out really
well and made a clean cut. The black things on the dowels are the
terminal strips that connect the hotwire to the voltage source. |
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| June 10, 2002. Here is a picture of the grove
cutter. I used a 10 amp battery charger to power it as the short thick
wire has very low resistance. The circuit breaker in the charger would
kick off every foot or so. When it did, I would pull up on the cutter
to keep the wire from getting stuck in the foam. All-in-all, pretty
easy. The cutter is MDF scrap I had with holes at 9" on center.
The wood reinforcement for the engine mount will be foamed into the groves. |
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| June 12, 2002. Made a gravity hotwire cutter using a
pair of lock pliers as a weight. The block is a scrap piece of MDF
with a hole in the middle through which nichrome wire was stretched by the
weight of the pliers. We drew a center line on the top so we could
control where the cut was being made relative to the line we drew on the
hull. Mark built the hotwire cutter. GREAT JOB MARK!!! |
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| July 4, 2002. Here Mark is cutting the slot in the
rear section of the hull for the engine mount boards. This is the
hotwire slot cutter powered by the battery charger. |
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| Another picture where Mark has finished the cut. The
yellow foam is the 2-part foam and does not cut very well and makes a big
stink when hotwired. So, we just cut it off with a saw. The
2-part foam was used to join the rear section to the rest of the hull. |
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| I got tired of the mess from the router when making the
slots for the attach strips. So, I made a hotwire attach slot
cutter. The cutter cuts a 2" wide slot and I am using 1.5" aluminum
flat stock for the attach strips. This is a great improvement! |
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| However, the short wire had too low a resistance for the
battery charger. So I made a resistor by coiling SS wire on a large
drill bit and wired it in series with the cutting wire. The coil gets
red hot with use but the cutter works very well and fast. The battery
charger does not even kick off. Life is good! |
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