Styrofoam wire cutting.

[David Hall 9]

Years ago, I had a go at cutting wing cores from blue foam. I got several wings from that method, but suffered a technical problem in that the wire was too slack (was taut before it heated), resulting in the wire dragging behind in the middle of the core.

I'd like to try again for some glider wing cores with thin sections. Is there a clear choice of wire type/gauge and bow design for a bow used to cut a 800mm core?

[PatMc]

You need to re-tension the wire once the power is switched on.

Use a Spanish windlass type type bow for easy tension adjustment - see this recent thread.

Edited By PatMc on 15/01/2019 19:33:37

[David Hall 9]

When I tried that, it seemed to stretch the wire.. which was near to red heat at the time, so perhaps too hot.  I was using nichrome wire, I forget what gauge. 

 

Edited By David Hall 9 on 15/01/2019 19:30:25

[David Hall 9]

Is stainless steel wire less prone to stretching whenre-tensioned whilst at cutting heat?

[Denis Watkins]

Even in a darkened room, you will not see the heat from a hot wire cutter, David

So the gear needs adjustment

Home made hot wire cutters are sprung too

[Former Member]

[This posting has been removed]

[PatMc]

Posted by David Hall 9 on 15/01/2019 19:29:30:

When I tried that, it seemed to stretch the wire.. which was near to red heat at the time, so perhaps too hot. I was using nichrome wire, I forget what gauge.

Edited By David Hall 9 on 15/01/2019 19:30:25

That's too hot by far, the wire shouldn't glow at all. Best reduce the temp & try on scrap pieces of foam adjusting the temp until the wire passes through the foam steadily but doesn't melt it much more than the wire dia.

[Former Member]

[This posting has been removed]

[David Hall 9]

Thanks for your replies, and the link to a similar discussion. Some experimentation may be needed.

[Simone Perfetti]

Hello, I solved a similar problem by applyng a small diameter spring to apply tension to the wire , when the wire is hot the elongation was around 7-10mm on 800mm of total lenght, I used a pull spring of 5 mm diameter, 40mm long, hope could be helpful for you

[John Duncker]

I used big elastic bands for tension, wing retaining size, and well stretched.

From memory 3 or 4 on the 36 inch bow and two on the 8 inch.

Thinking about it today and it was 20 years ago I set them up, the tension should have been the same on both so same number of bands required but I definitely used more bands on the longbow.

I was always a cut and shut measure by eyeball 'git her done' engineer.

Edited By John Duncker on 11/03/2019 21:11:46