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Hot Wire Foam Cutting

Old 11-25-2006, 09:05 AM
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Default Hot Wire Foam Cutting

Gentlemen,

[8D]I've heard that fishing line is ideal as cutting bow material ...........hmmmmmmmmmm. Of course nichrome wire can be purchased but some people say that it's not as good as fishing line? I'd like to make (2) cutting bows ......... the larger being 6 feet. Can anyone advise me on this? Thanks in advance...........

GDJ
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Old 11-25-2006, 09:15 AM
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Default RE: Hot Wire Foam Cutting

The advantage with the fishing line is that it can be stretched much tighter than nichrome - without it breaking.
With the wire stretched tighter, it will lag behind in the middle less than otherwise. I use stainless
steel fishing leader.
brad
Old 11-25-2006, 09:46 AM
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Default RE: Hot Wire Foam Cutting

I use 100 LB test fishing leader... works great!!!! and can be stretched VERY tight.... make sure your bow can handle the weight you are asking it to support.

Dan
Carolina Custom Aircraft
Old 11-25-2006, 10:22 AM
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Default RE: Hot Wire Foam Cutting

I see the advantage about having a taught bow...............funny I've never heard this mentioned before.........the benefit is obvious..........thanks guys,.

Old 11-25-2006, 11:43 AM
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Default RE: Hot Wire Foam Cutting

Whatever is used if the wire is hung virtically with a weight at the bottom, then the issue of sagging is minimised.
Makes for tricky handling but worth trying, especially with the length of 6ft in mind !!
I'd be thinking of breaking it into smaller sections.

Cheers
David
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Old 11-25-2006, 06:17 PM
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Default RE: Hot Wire Foam Cutting

Sag is probably the wrong word to be using, it's caused by the drag of the wire as it goes through the foam. Just that you're asking about what wire tells me you're new to foam cutting, so a little free advice is in order:

Don't cut polyurathane foam with hot wires.
White foam cuts easier, comes in lots of weights usally 1 to 2 pound per cubic foot. You want virgin foam.
Blue or pink foam is heavier, but stronger, cuts very smoothly. Blue is Dow, pink is Corning.
Spider foam is white but strong and expensive, used in surfboards.
EPP is rubbery, not strong in compression, but it doesn't break, used in slope flying wings, usally covered with packing tape.
Don't cut any thing longer than 24 inch, until you're good at it, 30 inchs would be the most I'd cut.

What kind of wing are you making? Are you covering it? With what? Are you vacuum bagging it?

Old 11-25-2006, 08:35 PM
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Default RE: Hot Wire Foam Cutting

Soarrich
Thanks for the gen. Yes............... I'm new to hot wire foam cutting ........... but..........I appreciate the advantages. I need to cut a wing for DOUBLETROUBLE .........(2) engine in-line design. I'll cover it with balsa .......... vacuum bagging is also something I'm looking in to but sounds exotic right now. VAC Power supplies to drive the hot wire were a problem until I stumbled on a schematic advertised on RC UNIVERSE that seemed workable ..... and safe. One other question about toxic fumes...........any concerns? Thanks again.

Old 11-25-2006, 09:45 PM
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Default RE: Hot Wire Foam Cutting

OK, if you're covering the foam with balsa use the white foam. It's called expanded bead foam. A good place to get it, unless you know of a foam outlet by you, is from a supplier that supplys the guys that put stucco on buildings, I was able to get it in 2 and 4 inch thickness'. Do a google on feathercut, it's a machine to cut foam, I bought a bar, some weights, and pullys for $15 to make one. Use formica scraps to make the airfoil templates.

How big is the wing?
Old 11-26-2006, 08:17 AM
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Default RE: Hot Wire Foam Cutting

There are numerous ways to cut foam cores, everyone has their favorite. I use an
old model train transformer to supply power to my bow(s). Some folks use
a 12 volt battery charger (not the one you charge your field box with, that is too
small). If you have deep pockets, a Variac variable power supply is great.
Brad
Old 11-26-2006, 09:22 AM
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Default RE: Hot Wire Foam Cutting

Soarrich

ref: http://www.rcstore.com/rs/general/plans.asp?catego=PL

The wingspan is 51 inches. I ordered the building plans from the Model Airplane News, on-line service (Plan 11982).........the ref should take you to the link............. The idea of having a model of this design intrigued me ..............maybe the appeal of having something different, eh?

GDJ
Halifax, Canada
Old 11-26-2006, 02:15 PM
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Default RE: Hot Wire Foam Cutting

OK, that looks real easy to do. I'd cut to 24 inch wing panels, the 51 inches is the wing tips added on.

You could use 1/16 balsa sheeting, or if you wanted to go real cheap, use poster board, it would be plenty strong for that wing and would cost less than $2 to sheet. A wing like this I would use contact adhesive to hold the sheeting on. You can do it with 3M 77 at about $9 a can one would do, or a waterbase contact adhesive for holding Formica on counter tops, it's about $6 a quart, which would do 10~15 of these wings. If you use balsa just cut the ailerons off the back of the wing, then cap the raw foam with 1/16 balsa. If you use poster board cut the cores so the TE is 1/4 inch thick, then use aileron stock for the ailerons.

The LE I would do one of two ways:

Balsa sheeting- Sheet one side of the core, then with the sheeting on the bottom, take a #11 blade held from the under the core trim the sheeting so that the blade is following the foam on the top of the core, then you sheet the top of the wing, going over the bottom sheeting, then trim vertically, sand the point off. Cut your ailerons off and cap them.

Poster board sheeting- Using 5 minute epoxy glue the 1/4 inch square balsa to the TE, the trim to the airfoil. Use contact adhesive, lay the poster board on a table, lay the foam core on it, the pick up the TE keeping the foam in contact with the poster board, roll the foam up so that it sticks to the LE, keep rolling the foam until you've gone all the way around the airfoil of foam. You should have a foam wing now.
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Old 11-26-2006, 02:33 PM
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Default RE: Hot Wire Foam Cutting

Soarrich

I can't thank you enough........very clear. I'll post a pic of the finished product...........don't expect it before Feb 07 though........new hardwood floors seem to be the priority around here.

GDJ. [sm=thumbup.gif]
Old 11-26-2006, 04:30 PM
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Default RE: Hot Wire Foam Cutting

OK, good luck. If you need anymore info feel free to ask.

This is a picture of a plane I scratchbuild using the balsa sheet, contact cement method.

88inch wingspan, no spars, 16 pounds flys great.
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Old 11-27-2006, 08:47 AM
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Default RE: Hot Wire Foam Cutting

Shorgum is the best glue I have used for sheeting foam cores so far.
IN that picture it doesn't show any LE cap. I believe that you will find the front of the wing harder to wrap sheeting around even wetting the wood.
Better results that way in a vaccum bag. I got the hot wire kit from aircraftspruce.com and put it in a box I got from Radio Shack added a 25' extension cord and a pair of aligator clips that attach to the wire. Foam core board? I have never tryed that for sheeting a wing but I would imagine if you scored the inside it would work...
Old 11-27-2006, 12:00 PM
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Default RE: Hot Wire Foam Cutting

ORIGINAL: charlieoneseven

Shorgum is the best glue I have used for sheeting foam cores so far.
I've heard it's good stuff, but have never used it, I like epoxy if I'm going to bag the wing, contact adhesive if I'm not. Some guys swear by Gorilla Glue, but I haven't try it either.

ORIGINAL: charlieoneseven

IN that picture it doesn't show any LE cap. I believe that you will find the front of the wing harder to wrap sheeting around even wetting the wood.
I don't put LE on wings I let the sheeting form it, I find it more accurate, as well as easier to do. I don't even put LEs on built up wings, the picture is of my Dancing HIppo sailplane without LE wood.

ORIGINAL: charlieoneseven

Foam core board? I have never tried that for sheeting a wing but I would imagine if you scored the inside it would work...
No, poster board, its thick ~.030 paper, comes in white and colors, 24 x 36 cost anywhere between $.50 and $1.00.

You have to do the LE of the foam a little different, you either cut it rounder or just sand the point off the LE. I guess you could fold it to make a sharp LE, you might even be able to fold it right on the foam, I've never tried that though.

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Old 12-07-2006, 09:20 PM
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Default RE: Hot Wire Foam Cutting

Your thinking outside the box there Rich. I supose with the light weight planes you can do what your doing.
Love the idea of leaving that big hunk O balsa off.
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Old 07-03-2008, 01:30 AM
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Default RE: Hot Wire Foam Cutting

If you want to go really inexpensive on sheeting the wing use banner paper from an office supply store. It is about the weight of the printer paper you use for your computer. I thin down white glue so that it can be brushed easily. To keep the paper from soaking up too much glue I pre-spray it with water before rolling on or brushing on the glue. Make sure to do both sides without taking a break as the paper will shrink as it dries and warp the wing otherwise. It will appear to be really heavy till the water in the glue evaporates. Once it dries cover the wing with your favorite low temp iron on film. A few drops of food color in the glue makes it easier to see where you applied it to the paper.
Bob

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