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scratch built hot wire cutter

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Old 12-01-2009, 04:14 PM
  #1
sir crashallot
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Default scratch built hot wire cutter

right guys and girls. just been reading a website and iv seen somthing done that could very well work for making foam core wings.

Ijust want to run the ideas past you all first before i go and try it.

in the picture is what iv seen, would this work if i built a frame 40inch long with some thin guitar wire or simular in place of the copper wire they have used.
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Old 12-01-2009, 04:26 PM
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Default RE: scratch built hot wire cutter

The problem that I see is that a lot of wire looses its strength when heated and you get a terrible mess. I have used nichrome wire for cutting foam wings and that didn't loose its tension. I used a large bow and made templates of the wing and a buddy and I cut a few in an evening. I am not sure how your red gadget will work. Give it a try and let us know.
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Old 12-01-2009, 04:39 PM
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Default RE: scratch built hot wire cutter

well thats not actualy mine, the theory is there though but it needs fine tuning for it to work and i was hopeing someone on here may have an idea towards it. i wont be using such thick wire i want to keep the wire down to a minimum to allow it to not work as a resistor.
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Old 12-01-2009, 06:25 PM
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Default RE: scratch built hot wire cutter

search for nichrome wire on ebay, should pick some up really cheaply.

My Hotwire cutter was homemade, it is 36 inches long and has two hinged end pieces. it looks like a long flat H. On one side I have some springs (You could use Bungee) to keep the tension and on the other I have the wire. Works of a car battery charger no probs

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Old 12-01-2009, 06:29 PM
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Default RE: scratch built hot wire cutter

thanks pal, have you any pictures of it. nice to hear someone from this side of the pond, especialy when it comes to tools that have to run off 240volt.
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Old 12-01-2009, 07:01 PM
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Default RE: scratch built hot wire cutter

The wire needs to act as a resistor to get hot. If it were a good conductor, it wouldn't get hot. That's the way those things work. Nichrome wire is your best bet. It's made to work when it's hot.
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Old 12-01-2009, 09:18 PM
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Default RE: scratch built hot wire cutter

A lot of people use stainless steel fishing leader as a cutting wire. It can be bought relatively cheaply and in bulk. Don't ask me the thickness though.
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Old 12-01-2009, 09:28 PM
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Default RE: scratch built hot wire cutter

.020" Stainless aircraft safety wire works very well, rarely breaks, not too much stretch. Nichrome sucks, it's much smokier and breaks much more easily.

In 25 years of hot wiring foam and dozens of planes all I've ever used is a $7 light dimmer switch. I cut with 115 VAC as the input to the dimmer. I burned out the original switch after about 15 years worth of use, so I'm "on" my 2nd one now.
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Old 12-01-2009, 09:36 PM
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Default RE: scratch built hot wire cutter

thanks for all the ideas guys, im taking every thing in from every one, soon as i get to build it over the weekend il put some pics up and some reports to you all
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Old 12-02-2009, 12:52 AM
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Default RE: scratch built hot wire cutter



I get my nichrome wire for my homemade foam cutter fromm www.pnjresources.com. They are cheap and fast delivery.

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Old 12-02-2009, 01:57 AM
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Default RE: scratch built hot wire cutter

SS leader wire Bass Pro (on line) had it the cheapest.
the set up in your pic would be sweet for cutting thin sheet foam for little electric planes etc. kind of like a band saw.
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Old 12-02-2009, 06:09 AM
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Default RE: scratch built hot wire cutter

You need a lot of tension in the cutting wire, otherwise it lags in the middle of the foam and does not cut the correct profile. that is why the bow needs at least 8 SWG piano / music wire (English size, not US size which is different ) and fairly short length too ( say 10 inches or so ) if you use wire 'legs'. A wooden bow rather like an old fashioned carpenters bow saw tensioned with cord is easier to make. Your gadget would be best left to make cutouts for servos and U/C blocks.
For cutting wire I use wire taken from an old electric fire element, the spiral wound type from 1950's & 60's ( English 240 volt type ) this makes many. many lengths of cutting wire.
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Old 12-02-2009, 09:42 AM
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Default RE: scratch built hot wire cutter

wel kdc the though of using it for cuting out servo hole locations and so forth never actualy ocourd to me. it would indeed if used correctly be perfect for that job. but the thought of being able to me turtle decks and foam veneared wings and tails and rudders and so forth would save time and weight in some cases. and it has its strength factors. i see this as a project that has some very good features that would be of great use to me and i doubt it would be a waste of time money and effort in building one. thanks for the idea kdc of using it for cutting servo holes out and so forth.
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Old 12-02-2009, 10:46 AM
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Default RE: scratch built hot wire cutter

If the gadget gets the temperature ( volts ) right for a small cutting wire it will be too cool for a much longer wire unless the longer wire is much thinner. So for a longer wire you need more volts to get sufficient temperature. Also if the tension is not sufficient you wreck the foam and waste money before you realise the wire has lagged in the middle! I suggest building a proper bow for wings & turtle decks, keeping the gadget intact for other jobs.

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Old 12-02-2009, 10:51 AM
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Default RE: scratch built hot wire cutter

yep i agree, well a friend is sending me some of that wire everyone is talking asbout the nicrome or somthing or other, il be building a bow from pvc tubing and il make a power source as i dont own a car battery charger. i did at one point till it got lent out then magicaly re apeared batterd and broken. i do however own a small hifi thats past its usable date, so il rob its 240volts to 12v powerpack inside and use a dimmer from maplins to control the power. il also put a fuse system in place too.
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Old 12-02-2009, 11:49 AM
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Default RE: scratch built hot wire cutter

pvc tube will probably bend under the strain. The temperature can be varied,if necessary by an aligator clip connection moved along the cutting wire, better than a dimmer I think.
Photos of my 'free' cutter are below. Tube is 3/4 inch OD aluminium from old TV aerial ( watch for weakness due to corrosion ), legs from 10SWG piano wire offcuts ( 8 SWG is really needed) with 'eye' bent into the end, cable is thick wires from scrapped washing machine, couple of bolts, washers and wingnuts ( ex TV aerial ) Note wooden plug (from tree which fell down in garden ) to insulate ends. cutting wire is from electric fire element. Power is from transformer from old gas boiler but and old car battery charger wiould suit ( they go wrong at the rectifier but 12 volt AC is OK ) or a car battery itself. Current needed is considerable.
You can see how much the 10 SWG is bent from right angle under the essential strain.
Better to copy the bow saw style in wood I think. Whether saw or foam cutter the strain has to be considerable to work well, therefore the construction too.
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Old 12-06-2009, 12:20 AM
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Default RE: scratch built hot wire cutter

My bow is just a 3/4" X 3" X 30" straight wood. I used a couple 12" aluminum arrow shafts drilled in at each end at an outward angle. I have been using a guitar E string for wire. Nichrome works well too. My power is an old electric train transformer and I can vary the heat range according to the foam and length of cut. If your wire is nice and tight and it is flexing, your either going too fast for the heat or your heat range is too cold. My transformer works best at the upper end of its range. With my bow setup, the arrow shafts have enough strength and flex to keep the right amount of tension. Mine hasn't failed me in 20 years.
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Old 12-06-2009, 10:24 AM
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Default RE: scratch built hot wire cutter

I recently made one of the soldering gun cutters as shown. I had a cheap Harbor Freight Iron (60 Watt) that I used for the experiment. I took a piece of wire Coat Hanger and bent it to roughly the shape of a servo. It works great for servo cutouts, but the wire is much too thick for anything bigger. What I did for larger cuts is to take two longer pieces of the hanger and bend them with two right angles, so when installed into the Iron, they resemble a football goalpost, just like in the picture. I bent a loop into the ends, and ran 1 strand of copper wire pulled from a 12ga stranded wire section. It cuts great for widths up to about 3 1/2", but not much more than that. The Soldering Iron just doesn't put out enough power for any more than that.
It is perfect though for small cutouts and trim cuts. If anyone's interested, I can post pics.
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Old 12-06-2009, 10:29 AM
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Default RE: scratch built hot wire cutter

right so he soldering iron is a no no if im wanting to cut foam wings. but it is a yes if i need to cut access holes for servos and landing gear blocks. so thats answered my question that it is not powerfull enough to use to cut wings, so now im off to look on the bay for a train controller, thanks guys
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Old 12-06-2009, 11:12 AM
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Default RE: scratch built hot wire cutter

There is really no need for a speed/voltage controller. The speed of the cut can be increased if it is hotter, or the lead can be connected along the nichrome wire with a crocodile clip if necessary. ( note someone on e-bay is selling nichrome wire lengths for a pound or two )
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Old 12-06-2009, 11:16 AM
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Default RE: scratch built hot wire cutter

i have the nichrome wire coming, its just iv managed to win a train controller for a £1, the train contoller is not just going to be used for the wire cutter, i need it for other things but if its usable with the wire cutter then its a great bonus
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Old 12-06-2009, 04:42 PM
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Default RE: scratch built hot wire cutter

I get nichrome wire from McMasterCarr. Remember that as one poster mentioned above, the wire acts as a resistor. Keep in mind that the resistance is a function of material, cross section area, and length. That soldering iron may put out adequate power for a short section of wire, but a bow long enough to cut wing cores may need more power.
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Old 12-07-2009, 10:42 AM
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Default RE: scratch built hot wire cutter

so what gauge ni-chrome wire DO we get then as there are many ?
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Old 12-07-2009, 11:57 AM
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Default RE: scratch built hot wire cutter

gd question, maybee someone should do a thread aqimed at the specs needed for a hot wire cutter and make the thread a sticky.
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