Making a hot wire

[ghcoe]

Thought I would post a "how to" on making a hot wire since I needed to make up another jig for a end cut.

So I am making a end cut to fit a 1"x2" piece of wood into the end of 2" foam. This is for my shelves in the galley as well as some other locations where I may want to add some strength to a joint or span. I am trying to use all the foam I have for the build to cut costs and waste. I am using left over pieces of foam from the bulk head and roof to make my galley shelves. These pieces are too short by themselves so I will need to join them together. I was just going to glue the foam together, but thought that it would be nice to have some extra support for the center of the shelf and for the joint itself.

Before end cut

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First I need a block of wood. A 2"x4" works good.

Wood block

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Then I will mark the wood where I want the holes for the wire to come through. I want the cut in the center of the foam so I measured from the edge how far in I need to be and then for the width of the cut.

Marking wood for wire holes

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[ghcoe]

Now I drill holes where I marked the wood for the wire to come through the 2"x4".

Drilling holes for the wire

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I use pencils to keep the wires where I want them and also to use as a attachment point for power. You can drill holes now for the pencils which would be a bit easier than doing them after you put the wire in like this picture shows.

Holes for pencils

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So when using a hot wire you want the wire to get hot enough to cut at a good speed, but not so hot that it bends easy. Being that I am using a common car battery charger for my power source I can not change the power to the jig, so I have to change the power with the jig. The easiest way was to find how long a wire I needed to get the wire hot, but not too hot. I found 3 feet of .030 welding wire to be just about right for my particular charger set on 2 amp charge. The shorter the wire the hotter it will get, longer cooler, get it?

3 feet of wire

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[ghcoe]

Now I take the wire and find where the middle is and feed the wire through the holes I drilled through the 2"x4". I like to have equal parts of the wire coming through on the other side.

Wire through the jig

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Now I want to make one side of the wire coming through the 2"x4" solid. I use a screw to screw into the same hole the wire comes through. This will lock the wire so it will not move around.

Screw to hold wire in place

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I bend the wire to the side to make it easier to install the screw.

Screw installed

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[ghcoe]

So now that I have the wire solid on one side I can now make the wire shape the way I want. In this case I want half the cut depth of my 1"x2". It is easiest to cut a piece of wood the depth you want the cut, or in some cases the shape of the cut you want.

3/4" jig

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Now I can pull the loose side of the wire through the block and get the wire close to where I want it. I use a little help from a hammer and needle nose pliers. Just a little tap with the hammer to get the wire around the edge of the block. I am trying to get some of the slack out of the wire so I can get it close to the shape I want.

A little help

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And a little tweaking with the pliers.

A little help

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[ghcoe]

Now I lock the other side of the wire in place with another screw.

Both sides locked in place

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The wire shaped for the cut.

Final wire shape

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Now I have 3 feet of wire we need to get out of the way. I use two pencils. Make sure they are wood pencils, I found one to be made out of plastic and it melted through.
Now I wrap the wire around the pencils. I make sure the wires do not touch anywhere in the wrap. If the touch it will make a short and make the wire burn hotter. By making this wire wrap I can also control the wire temp some by placing the power clips higher or lower on the pencils. Lower = hotter because you are shortening the length the current is going through. Higher = cooler by more wire the current is going through.

Two pencils

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[ghcoe]

Now that the wires are wraped around the pencils I can install them into the holes I cut earlier.

Pencils and wires finished

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And I am ready to power up. With his jig I can make this cut by using a straight edge. I use gravity for my cuts. You can use hand power, it takes a bit of practice to get it just right. You want to make a steady cut, if you go too fast then you could cause the wire to bend and make a poor cut. If you go too slow then the wire melt excess foam and make a poor cut.

Powered up

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Gravity seems to work the best for a nice constant speed.

http://www.youtube.com/watch?v=1h8EGYTb ... e=youtu.be

[ghcoe]

So, in most cases I would use a straight edge for my cuts. In this case I want to make a fence so that I can make a end cut into the foam. To do this I need to add a fence to this jig. I will just be adding a 1/4" peice of wood to the edge of my jig. This will make a built in straight edge to run along the edge of the foam.

Making a fence

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Test cuts are made.

End cut

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Success....

Smooth cut

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[ghcoe]

So now I can join my two pieces of foam and have a strong inner support and joint. I will be making another jig similar to this one, but with a deeper cut to install a 1"x2" piece of wood all the way into the end of a 2" piece of foam for extra support along the front of the shelves.

The finished result

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Hope this helps and happy foaming......

[Fishingtomatoseed]

Thank you for the write up. Always wanted to know.

[GPW]

[Wolffarmer]

Thanks for the write up. By welders wire I figure you mean the wire from what I call a wire feed welder, non flux core. Correct? Also in lew of pencils one could use a dowel, most any small strip of wood, Make it a art piece with a glass rod, colored even. Don't drop it.

Edit And I would caution that not all 2 amp chargers are 2 amp. Your heat may be different.

[cleonard]

Thanks for the nice write up and pics.

I had a hot wire setup back when I was doing RC planes. I also used a fixed power supply which in my case was just a low voltage transformer. On my setup I put the variable resistor at the power supply. That made the various tools a little simpler to make and a bit more streamlined.

You might have set you charger to 2 amps, but I'm pretty sure it's delivering more like 10 amps. It takes a good amount of current to heat that large of wire.

[ghcoe]

Thanks for the write up. By welders wire I figure you mean the wire from what I call a wire feed welder, non flux core. Correct? Also in lew of pencils one could use a dowel, most any small strip of wood, Make it a art piece with a glass rod, colored even. Don't drop it.

Edit And I would caution that not all 2 amp chargers are 2 amp. Your heat may be different.

Yes, standard mig welding wire non-flux core .30.

I had pencils, so yes, you could use anthing that would work for you to wrap your wire around.

3 feet worked for me. That is why I mentioned that you would want to play some with the length to get the right heat. Shorter = hotter, Longer = colder. Also by wrapping the wire around the pencil you can control heat by placing the charger clamps higher or lower on the wire wrap.

[GuitarPhotog]

Here's a great site on hot wire foam cutters. It offers calculators so you can determine the current required to heat various kinds of wire to the necessary temps, and lots of sources for low-voltage power supplies and nichorme wire.

I suggest using nichrome wire (available on Amazon and many hobby shops) rather than welding wire. It's predictable, stable and doesn't burn up due to oxidation as quickly.

http://hotwirefoamcutterinfo.com/Hot_Wi ... ction.html

I build two cutters when I was insulating the interior of my trailer, one for cutting slabs from the sheet, and one for making channels and kerfs to fit around the existing trailer ribs. One was powered by a "wall wart" on a lamp dimmer, and the other (the shape cutter) used 2 high-current 1.5 VDC batteries, and could be used hand held. (Sorry no pix of either, they were one-project tools.)

<Chas>

[ghcoe]

I have found the welding wire to work quite well at the temp I am using it at. I have made quite a few cuts with my straight cutter and I see no metal deterioration at all. I have not played with the nichrome wire so I can not compare the two, but for what I had lying around welding wire works well. Also, I am not sure if the nichrome wire will hold a shape or not. I was on another web site where they were using stainless steel welding wire to make very intricate dado's. They mentioned that the stainless steel held the shape of the dado better than other wire they had used. That is where I got the idea to use the mig wire I had.