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Foam wing core woes

Old 02-24-2007, 08:00 PM
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Default Foam wing core woes

I'm about halfway through my first scratch build. What is holding me up now is cutting the foam wing cores.

I built a good hotwire cutter, made templates out of countertop laminate, and am using eps foam.

I have cut several cores, they all come out with the center of the core thinner than the ends. i.e., the root and tip are acurate to the templates, but the wing gets thinner as you move toward the center.

I am working on a flat surface, the wire is tight, heat seems ok. Wire is 0.020 ss fishing wire, cuts very well with the dimmer switch on my cutter at about half-way.

It is only a 24-inch core, I am at my wit's end as to why they keep coming out so poorly.

Has anyone had this problem, or does anyone know what's going on? I really appreciate any help, I'm about ready to chuck the whole project.

Old 02-24-2007, 08:44 PM
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Default RE: Foam wing core woes

sounds like the wire is too hot or the wire is becoming loose as it gets hot and becomes longer from expansion.most foam cutting wire is nichrome or music wire not having used ss fishline I cannot comment on if that is the problem.I have cuts lots of cores and never had the problem you describe.what hapens when you take a small scrap of foam and try cutting it in half at the center of the bow slowly?how much of the foam is melting away from the wire ?
Old 02-24-2007, 09:07 PM
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Default RE: Foam wing core woes

Stu--Sounds like the wire is too hot. Turn the power down so that you cut about an inch every 3--5 seconds with slight resistance. If the wire is going through the foam with no resistance being felt than the wire is too hot. The other thing you can try is higher tension on the wire in case it is stretching too much when it gets hot.

A good way to test the heat is to cut a scrap piece and see how long the foam "whiskers" are when the wire exits the foam. I like them to be two to three inches long. Wipe the wire clean and go to it...
Old 02-27-2007, 10:17 AM
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Default RE: Foam wing core woes

Our origional hot wire set ups used a spring at the one end to take up any slack in case we ran a little too much current through the wire.

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