Making a hot wire

Canvas covered foamies (Thrifty Alternatives...)

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Re: Making a hot wire

Postby Tyrtill » Wed Apr 17, 2019 7:23 pm

I made a long cut foam board cutter currently it 4' but I will be trying 8' tomorrow (hopefully not to much resistance)


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Using picture hanging wire (or probably .030 welding wire) I made a 5 ft length attached to a board with a screw. On the other end was a bolt that was set below a platform for the foam board. Just put the wire on the line and turn on the juice and you get a nice straight cut.
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Re: Making a hot wire

Postby ghcoe » Wed Apr 17, 2019 8:50 pm

Good Job! :thumbsup:
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Re: Making a hot wire

Postby GPW » Thu Apr 18, 2019 6:12 am

A Pivot wire system like that , can also cut out tapered shapes with a template on the other end … :thinking: Check this guy out …. https://hackaday.com/2015/05/14/move-ov ... you-wings/ Any ideas ???
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Re: Making a hot wire

Postby Tyrtill » Thu Apr 18, 2019 8:18 am

8 FT was a real slow cut ~ 1 minute for an 8 foot cut but it looks just as nice as the other cut.

I did see someone using a template and it made me think of useing shelf brackets or L Brackets to make perfectly straight and square cuts every time but my "by hand" method seems to be giving me reasonable results.

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Re: Making a hot wire

Postby featherliteCT1 » Thu Apr 18, 2019 5:45 pm

Thanks for posting the video ... your method appears to work great!
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Re: Making a hot wire

Postby GPW » Fri Apr 19, 2019 6:14 am

T’ , for shorter cuts with our bow we use the gravity method laying the wire across the foam , bow underneath , then turn on the electricity and the hot wire just falls through the foam , producing exact cuts every time , and if we want an angled cut we just tilt the foam …
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Re: Making a hot wire

Postby Hamilton Felix » Sun Jun 02, 2019 11:27 am

This is all interesting. Sounds like it does not take a lot of heat to cut foam.

I have a Harbor Freight "hot knife," but it's rather thick, something I bought to work with synthetic rope.

I was thinking that with the right wire, I should be able to make something to work off of my old Weller D650 soldering gun. I see many others have done so. That is 200 or 300 watts, depending on trigger position. Might be overkill. I wish I knew what happened to my old 100/140 watt Weller 8200 N. I inherited an old Craftsman gun that I think is 120 watt, but it doesn't appear to be designed to replace its tips. Might sacrifice that one to science...

Too bad Weller doesn't offer foam tips. They do make plastic working tips. Oh well, we'll make our own. :)
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Re: Making a hot wire

Postby GPW » Mon Jun 03, 2019 6:03 am

Ham, getting the heat right is important!!! …. Too little heat doesn’t cut , too hot makes big Wallowing cuts … It’s most practical to make a Bow type hot wire and use some type of adjustable DC power supply ( like an old train transformer) . We still use an old Variac , but that puts low AC on the bow ( dangerous) …
Over the years we’ve cut literally hundreds of Foam wings for model planes …. Once you do a few , you can get great results , and with smaller cutting wires and a pair of templates , you can cut most any shape you want ...the sky is the limit ... :thumbsup:

Ps. our Favorite Hot wire is still Stainless steel Fishing leader material ( solid) … Cuts great , lasts a long time , and it’s cheap and available ;) … Remember you don’t want the wire glowing HOT , just hot enough to melt the foam …

Ps , Don’t do like I did using an AC plug at the wire end ( fits my Variac) , as someone might accidentally plug it in the wall … :frightened: Big alligator clips work great instead … With a wire , polarity doesn’t seem to matter ...
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Re: Making a hot wire

Postby Tyrtill » Mon Jun 03, 2019 7:40 am

With mine for an 8' cut I'm using around 200 watts (8 to 10 amps at 24v). In the case of the wire I'm using 6-10 Amps cuts pretty well but over that it cuts about 1/8" and if you let it stay put too long it can cut almost 1/2".
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Re: Making a hot wire

Postby Hamilton Felix » Mon Jun 03, 2019 10:52 pm

LOL! Someone would only plug that directly into 120VAC once! :lol:

I can see how some kind of variable power supply is the way to go. If your cutter is relatively low wattage, there might even be some dimmers that would work. My soldering gun gives you 300 watts, 200 watts, or nothing. Not great options.

I’ll have to poke around in my shop. :thinking: Maybe there’s a forgotten old variac at work... ;)

I like that bow saw design above. I might even have an old bow saw around here.
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Re: Making a hot wire

Postby GPW » Tue Jun 04, 2019 4:45 am

And just sayin’, my Variac is fused for 5 amps , and we’ve only blown the fuse once in about 30 years … I only turn it up slowly till it begins to cut , that's all ... :thumbsup:
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