Re: [RCSE] Foam cutting - curls up

[Rcsoar4fun]

I have had foam cores do this before, always with pink or blue foam, not 
white.  I have later bagged this wings, with no noticeable effects.  I think 
its just stress that is built into the foam that is relived when it is cut.  
As long as the wing is sheeted on a flat surface it should remain flat.  

Kristopher
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Re: [RCSE] Foam cutting - curls up

[mikel]

Welcome to extruded foam sheets.  The pink Foamular (not Dow) foam you
were using can have quite a bit of stress in the skins.  You have two
options.  One is to shave a thin layer off the each side, the other is
to score the top and bottom of the sheet before you cut it.   Using a
plank in addition to the weights to keep the foam blank flat helps too. 
You will still end up with core beds that look like hobie hawk wings,
but your core should be fairly flat.
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RE: [RCSE] Foam cutting - curls up

[Scobie Puchtler or Sarah Felstiner]

Pink and blue foam are produced with some surface tension in the skin-like
layer on the top and bottom surfaces. If you spraymount down a block of pink
foam and cut a layer off the top using your hotwire, that layer will curl to
some extent almost every time. Generally the thinner that first cut off
piece is, the more it will curl. If that layer you cut off was created by
actually making the bottom cut for your wing, then it can be distressing,
because the piece of foam that you're already thinking of as 'your wing'
seems woefully distorted. If the curl is not too extreme and you can weight
the piece back down into the bed thoroughly and do the top cut, chances are
your finished wing will be quite straight, because you will have gotten rid
of the top 'manufactured surface' which is where most of the 'pre-tension'
is in the foam.

If you are set up to cut top surface first, then after your first cut, all
you'll have is a warped top wing bed, probably not much concern. Just cut
the bottom cut and you'll see that the wing itself is fine, though when you
unstick the bottom bed from the table, you may find that it too has some
curve. It is not at all unusual to get a perfectly straight wing core with
top and bottom beds slightly (or not so slightly) curved, kinda like
parentheses around a straight line: (!)

If the curling is extreme or really interfering with getting a good core,
I've heard of folks making a straight set of templates to just shave a slab
off the top and bottom of the foam panel before they even get started
cutting the actual foil profile, but it's worth avoiding this if you can,
just because it's alot of extra fuss.

Don't panic, cutting foam is awesome, and you'll soon work out the bugs.
Feel free to ask further questions or write back if anything here is
unclear. Hope this helps.


Lift,
Scobie in Seattle

 -Original Message-
 From: David A. Enete [mailto:[EMAIL PROTECTED]]
 Sent: Sunday, April 23, 2000 8:48 AM
 To: [EMAIL PROTECTED]
 Subject: [RCSE] Foam cutting - curls up


 I tried cutting foam for the first time last night and got a curly plank.

 The blank was Dow pink foam (Home Depot).
 I had the blank weighted down.
 I had templates at each end (pinned to the blank).
 The wire was .018 stainless steel.
 The cut didn't happen overly fast, just at a constant speed.

 So, now I've got a piece of foam that looks like a Hobie Hawk wing.

 What gives?


 - David

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