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Hot wire Foam Cutter question


Paul Harris 5
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Hi all

I am going to make myself a hot wire foam cutter to have a go at making my own wings, I have most things sorted but have a question regarding the wire used.

I understand it needs to nichrome wire but a quick search on eBay brings up a biwildering selection of thickness's

The power supply I was going to use is from an old computer and gives both 5 & 12 volts at a minimum of around 30 amps. So what thickness of wire should I be looking for. I have small commercial unit but it only cuts upto 6 inch wide and the wire supplied with that is around 0.24mm would that be suitable for a cutter wide enough for 3 to 4 foot or do I need a thicker wire.

Thanks for any help with this.

Paul

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I've used wire salvaged from a 1kW electric fire element for a bow 39" long(total cutting length). Wire was tensioned by 'bungy cord'. Power was from a 30V 6A variable bench power supply. Trial and error test cuts on spare foam before the proper job. Only used it on EPS foam years back, although I still have it. Made foam Watt 4 wings(lots) and foam RC combat wings(lots, short life expectancy) amongst others.

HTH

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Paul,

I do use nichrome wire and found it to work fine - I must be doing something from MattyB so I'll give details:

I use 1.3m of 26 guage wire that I got from Maplins (found 28 guage too thin).

I use a 5A adjustable power suply (a replacement laptop powersupply) on 20v (its selectable from 12 to 22v in 1v steps and this seems to provide me with enough control over the heat in the wire.

I use a really cheap and chearful setup for the swing arm cutter - it uses monofillament fishing linean eye hooks (the type for you use for hanging pictures on walls). The monofillament line is virtually frictionless going through the eyehooks (i.e. no need for wheels). When you want to change the cutting ratio (tapper of the wing) you just unscrew the eye hook and screw back into new position.

One issue - my wire looks thicker (.45 mmOD) than MattyB's stainless steel, so you might have to allow for a slightly wider cut.

For the bow I use about 2m of 25mm OD white water waste pipe which I bend into a curve and tension when I attach the nichrome.

Usual warnings about protective gear (especially eye protection) apply.

Pics at https://pssmodels.wordpress.com/foam-wings/foam-cutter-setup/

I suspect the nice looking stuff that MattyB has cuts more consistently.

Mike

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  • 1 year later...

1st things 1st Paul, 30 Amps will melt flesh and readjust a heartbeat, maybe to zero, so be careful as any junk power supply is unauthorised, etc etc

Nickel Chrome wire of minimal thickness will glow cherry red without breaking

And the heat required for foam cutting is no where near this heat, in fact, is barely detectable by eye

I am waffling, hoping you consider casing up the 30 amps properly

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I have been told of a way that might interest some that does not require a PSU etc.

The wire used is from Maplin.

The equipment is a Brushed ESC, together with a Rx and Tx and a 3s Lipo. The temperature of the wire being controlled by throttle control via the Rx and ESC.

I have never tried it, although apparently others in the club use the set up.

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The last one I made ( many years ago) used 0.8mm stainless MIG. Welding wire and worked a treat. The biggest thing for me is keeping the wire taught as it goes baggy when heated up. I've been working toward making another (a divorce lost me the old one). I intend to put a bellcrank on one end and tension the wire with a spring so the tension remains reasonably constant. Otherwise you need to have the tension absurdly high when cold to keep a reasonable tension when hot. Temperature is colder than you think as the foam, being a good insulator, causes the wire to heat up when you enter the cut. The frame I have made is 20mm steel conduit, like a large hacksaw frame.

Shaunie.

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Whilst it's true that cardiac damage in electrocution is measured in amps it's a function of volts. . And it therefore depends on resistance or impedence. A spanner across a car battery at 12v will glow cherry red. Me holding the terminals of a psu at 30v will supply zero amps.
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The link that Master Crash Man has provided is very good in my opinion. I particularly like the additional video on how to drill for a spar. The reasons being the simplicity, combined with effectiveness.

Although the bow shown is simple, I have seen a simpler bow, which does work. This bow was made simply from a broom/brush stave or handle. The stave was made longer than the wings to be cut. A hole drilled at each end, along the central axis for a short distance. Into each end a length of Piano wire was pushed/driven in. Each end was then bent through something less than 90 degrees. It is the natural spring of the piano wire that is used for tensioning.

However I have forgotten how the Maplin wire was attached. Again crocodile clips were used to supply the power.

In that case a battery charger was used.

I am seriously considering making a device for myself, again using a Lipo and probably a old 35 Rx and Tx, as I am sure that somewhere I will have a brushed motor controller.

It seems that it is simpler than ever to have a go.

Edited By Erfolg on 11/08/2016 10:58:12

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  • 8 months later...

hi there all

Been looking at Matty B vid. i have been looking at power supply for a hot wire cutter and saw this power supply the Fusion 200w twin adjustable at sussex model center would this be any good say for a 1 meter bow.

will

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Did some hot wire cutting many years ago and had really good results. The only caveat was the very unpleasant fumes that came from the white foam that I was using and initially made me feel very ill until I improved ventilation in my work room.

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Posted by willhappy on 09/05/2017 22:21:13:

hi there all

Been looking at Matty B vid. i have been looking at power supply for a hot wire cutter and saw this power supply the Fusion 200w twin adjustable at sussex model center would this be any good say for a 1 meter bow.

will

Yes, that will be fine. As others have posted though there are cheaper ways to do this that avoid you purchasing a new PSU (some chargers have a foam wire cutting output, and you can also use a brushed ESC plus 3 lipo setup too).

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In our mass build it was the quality of the (wood) templates that were the defining factor - they started off great, but the more wings we cut the more damaged they became and the more rippled the wings were. Getting the right (synthetic) material for them is key - I now hav some of the propoer stuff, but it's so long since I bought any I can't remember what it is called!

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