straightening out wire for foam cutting bow

I´ve been building a DIY foam cutting power supply, it will soon be ready. The next step will then be to build a bow for the hot-wire. Now, a friend of mine gave me a coiled heating wire from a ceramic oven and I´m hoping I could use this. Took me an evening to uncoil the stuff, managed to do it with no nicks in the wire, but it´s a bit wavy still and just forming it with my fingers or pulling on it won´t straighten it out. Any ideas on how I could get it straight and smooth?
Cheers, Ken

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The tension of the bow should be able pull the wire straight and tight. Foam cutting wire is very thin, on the order of .020", or .5mm, preferably stainless steel. I suspect that oven wire is probably quite thick.

I built a DIY foam cutter last year.
I have used cheap picture hanging wire 22 gauge. It works ok, but it stretches, and breaks easily.
The best wire I have used so far is .014 diameter stainless steel fishing leader. I works great.
I have never tried Ni-chrome wire, I can't find it locally.
Any wire thats small, yet doesn't stretch much when heated will work.
On Tue, 12 Aug 2003 12:41:14 +0300, "Ken Mattsson"
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The best stuff is what commercial cutters use. That is Inconel and .015 is a good starting size for 20-40 volt supplies.

More than likely, that is nichrome wire and really isn't the best stuff for foam cutting. It stretches a lot and is hard to hold tension. The wire you really want is Inconel. If you are using 20-40 volts, then wire near .015 diameter will work well.

Me thinks you are waisting your time. I use Tekoa's carbon wire it costs $4.50 for an 8' length and lasts foreever if you don't miss handle it. The wire is called T370 is used to make coil springs. It doesn't streach like like ni-crome. I have a 54" bow that I use to cut Q500 wings and the wire in it is about 6 years old and has cut about 50 wings.
So to me the bother of unwinding a coil is just not worth $4.50. Kind of like making your own CA. Tekoa is here http://www.tekoa.com/catalog.html
And there's a distributor here. http://www.acp-composites.com/ACP-CAT.HTM http://www.acp-composites.com/acp-FoamCuttingEquipment.pdf
IMHO, Stan D.
On Tue, 12 Aug 2003 12:41:14 +0300, "Ken Mattsson"
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Ken Mattsson wrote:
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I built a very easy foam cutting bow that works great. I used a piece of metal electrical conduit from the hardware store as a handle. I bent it into a bow shape with a pipe bender. I stuck a piece of dowel into each end, drilled through it and secured it with a screw. The thick dowel sticks out of each end about an inch or so. I drilled through both dowels and put bolts through them to attach the wire to. The bolts have the type of heads that are flattened for turning with your fingers. I drilled little holes in the heads and attached the wire, which was stainless fishing leader. Then I wired it to a cord with medium sized battery clamps on the ends. Whenever I want to use it, I just attach it to a car battery. It works great, and it cost well under ten dollars.

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Ken,
If you find a place to buy fishing leader in lengths longer than 15cm here, please let me know about it! I have had to bring it from the UK on visits (to use as closed-loop wire).
How's that simulator you bought from me doing?

Thank you guys for all the great advice I got! I´ll try to straighten out the wire I have first, If I don´t succeed I´ll start shopping around for other wire types.
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Dave,
It seems that most fishing shops in Finland have a somewhat restricted sortiment. I´ve been looking for suitable fishing string (or do you call it fishing line???) for a bungee launcher for sailplanes, but the shops mostly only have quite thin string and even less of string in 100 meter reels or more. By fishing leader, do you mean that first length of wire from the lure, used to avoid getting the line cut off by too aggressive fish? =)) If I run into this kind of wire sold by the meter, I´ll be sure to drop you a line.
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Oh, I learned to hover in different positions, with tail in and side in. Then my studies and work took the best of me and haven´t played around with it that much after this. Still, I´m very pleased with it and wouldn´t sell it, not even if I could afford the Realflight G2. There is something very cosy about the CSM v.10. Still haven´t found a Piccolo heli for the sim though, that´s to be honest the real reason I eventually stopped using it. The Piccolo is, I´m afraid to say, some kind of obsession to me, I will get a real one before I die, even if I die trying to get one=)) Those little helis just are so darned expensive and it seems that even if I try to talk smoothly in German with the guys at Ikarus, they just don´t seem to get it, that they need to give me a special deal in order to save the world and make it a better place to live in;)
Still, in case there is any friendly Piccolo nut with a suitable setup for the CSM sim reading this, I´d be very happy indeed if he/she would be willing to send me the settings. Tried asking around for a CSM Piccolo in heli groups once, but nobody had done it and I cant since I have no idear of how the Piccolo should act to get it right. As a parentesis I have to say that for owners of real Piccolos there are some VERY nice web sites out there, very fine sites indeed.
Oh well, ´nough said about helis. It´s been great fun building this foam cutter power, and again a big thanks to the kind soul who put out the building description on the net for all and everyone to enjoy. It´s great fun building one´s own tools.
Cheers, Ken Finland

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Fishing leader, or trace line as it seems to be called in the UK, is indeed the thin metal line (usually with a nylon coating) that is used to defeat the teeth of the pike. In the UK it can be bought on reels, but I have seen it only in short lengths here.
For really thick nylon monofilament, try Kärkkäinen; not the model dept, but the fishing section. I saw some line about 2mm thick when I was there a few weeks ago. Last summer I was towing up a 3½ metre glider with some line I got from Prisma! Nordic sports in Kouvola also have some decent line.
My heli addiction has finally been cured, only two left now and both for sale. My only experience with a micro heli was a friends Hornet - about 100 times harder to fly than a glow heli! I saw a guy with a 'made in Finland' micro heli a few weeks ago - he flew it IN the SIL shop! I was told there are plans to go into production. At least then you could order your spares in Finnish!

Email me your address.

Dave,
I can get Inconel fairly inexpensive ($1.75/foot in small quantities) and I have a fair amount right now at about half that cost. Inconel is a lot better than stainless. It takes less power to heat and doesn't stretch as much.
Send me a few Euros and I'll set you up with about 10 feet of it.

Thanks for the offer, Paul, but it was Ken who was after the wire, not me. I still prefer to build using old-fashioned wood!

tie a 3 kg rock to your head and jump up and down on the spot for ten minutes. That should give you a headache about as quickly as trying to straigten out wire, Ha, ha. ;b
I must admit, this suggestion seems the best to me:
Me thinks you are waisting your time. I use Tekoa's carbon wire it costs $4.50 for an 8' length and lasts foreever if you don't miss handle it. The wire is called T370 is used to make coil springs. It doesn't streach like like ni-crome. I have a 54" bow that I use to cut Q500 wings and the wire in it is about 6 years old and has cut about 50 wings.
So to me the bother of unwinding a coil is just not worth $4.50. Kind of like making your own CA. Tekoa is here http://www.tekoa.com/catalog.html
And there's a distributor here. http://www.acp-composites.com/ACP-CAT.HTM http://www.acp-composites.com/acp-F...ngEquipment.pdf
IMHO, Stan D.
-- Randori ----------------------------------------------------------------------------------- Posted from the RCGroups.com Discussion Forums. Visit us at http://www.rcgroups.com <------- Win free R/C Gear! View this thread at rcgroups.com: http://www.rcgroups.com/forums/showthread.php?threadid 1767

Fritz Bien wrote:
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Guitar strings at 10-15 thou are easy to find and good allegedly. They are gerenrally plated tho, so won't last as well as stainless.
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I finished the DIY foam power supply recently and tried it out with 48" and 24" long wire from the ceramic oven. Well, it didn´t work out that well. This wire is 0.5 mm in diameter and while the power supply is designed to work with the above mentioned lengths of wire, I had to use it with the switch turned to the 48" length position with the 24" long wire to get even e very low intensity reddish glow. Seems pretty clear I need a thinner and more easily heated wire. So, what would be a better pick, inconel 0.015 or that other stuff, carbon wire which they sell at the feathercut site?
By the way, here is a link to the DIY power supply I built:
http://nsrca.org/technical/tip_tricks/foam_cutter/foam_cutting_power_supply.htm
I haven´t yet started building the bows, thought I´d surf the net a bit first to see what sorts of bows can be built. Something that could be easily taken apart and set up again would be nice.
Ken From the land of the...well, very very many...lakes.

A dull reddish glow is WAY too hot for foam cutting! My wires do not glow at all and cut as fast as my macine travels. You should try tocut some foam before changing anything.
You will also find that Inconel takes a lot less power to cut foam.

The wire shouldn't get red hot. The wire only needs to be hot enough to slowly melt its way thru the foam.
If the wire is too hot you'll melt a 1/4" gap thru the foam instead of a gap the thickness of the wire.
The bow needs to be made from wood or either use insulators to connect the wire to the bow. You don't want electricity traveling thru the bow trying to heat the bow instead of the wire.
If you use metal templates to shape of the foam, be sure there is no electrial path between the templates.
I once tried using 2 aluminum rulers clamped around a block of foam to square cut the end. I was using a metal clamp to secure the metal rulers. The electricity traveled from the wire to the ruler, thru the clamp, to the other ruler, back to the wire on the other side. The wire on both sides was hot, the wire in between the rulers was cold and would not cut.
You already have your Power Supply, but the one I use is a $12 Radio Shack 2.5 Amp 120VAC-input 25VAC-output Transformer connected to a $3 rotary-dial dimmer switch. It provides an infinitly adjustable heat range for any length bow and any type foam, white, pink, blue.
The dimmer switch controls the input voltage, with directly controls the output voltage(heat).
On Mon, 18 Aug 2003 16:34:55 +0300, "Ken Mattsson"
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Ken, what do you plan to cover the foam cores with? I ask as I have had some problems with veneered foam wings since I moved here, in that the veneer has split due to the very low humidity here. I never had that problem when I lived in England!

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Well Dave, having been to England a couple of times and always encountered rain, I can see your problem! =)) Still, the same happens to me wherever I go here in Finland, been called the rainman by my local friends...
As to what material to use for covering the cores, I must say I´m a newbie to this subject too. Still, I believe most guys over here use balsa sheets for this, mainly because it´s easily available. You can get thin plywood too, from the model shops, but as to the suitability of this for sheeting foam cores, I´m not that well informed. You might want to post your question to this group: sfnet.harrastus.pienoismallit or sfnet.harrastus.ilmailu. You can probably post in English if you like, the guys in the groups are mostly good at English. I have always received good advice there, still I like to use these international newsgroups too just because one can reach so much more fellow enthusiasts this way.
By the way, I was kind of hoping I could get away WITHOUT sheeting the cores for the basic trainer wings I´m contemplating, but maybe that would make the wings too weak...? Still, there´s no sheeting on the Sturdybirdy II or Duraplane wings, the former is strengthened by applying strips of glassfiber reinforced tape (from your favourite "rautakauppa" over here) over and under it, lengthwise, the latter has a metal U-channel in it (I think). I have a Sturdybirdy and the tape trick seems to work, doesn´t even look too bad when covered with a suitable iron-on covering film.
Hope this helps, if not, just post your question in the above mentioned Finnish newsgroups, you will surely be helped. If that doesn´t work, drop me a line and I´ll translate your question into Finnish for you.
Ok, have to run now to get the necessary stuff for a cutting bow!
Cheers, Ken Sipoo Finland