cutting foam

[alex nicol]

Ive just been messing about with a home made foam cutter powered with a PC PSU controlled with a dimmer switch. I've tried various types of cutting wire from 0.27 - 0.6 nichrome wire ti lay straight control line wire. ideally I'm looking to cut a 30" span section.

Has anybody else tried this and if so what wire/PSU did you use

[PatMc]

I've used aprox 0.45mm x 1mtre of nichrome wire straightened from a replacement old fashioned electric fire spire element.

Successful power sources have been : a 240v - 50v ac transformer with the output 1/2 wave rectified to give 25v & 12v car battery in series with a 12v car battery charger, again giving aprox 25v output. Never bothered to "fine tune" the voltage.

All PC PSU's I've converted to power chargers have had 12v - 14v DC outputs, what voltage are you getting & how is the dimmer connected ?

[Martin McIntosh]

I now have a powerful 24V supply but a couple of 12V batteries or one of these in series with a 12V charger also works. My wire is from Nexus but I have also used a fire element. The temperature is controlled by wrapping extra wire round one end until it feels right for the job. The wooden contraption to hold the wire is tensioned with strimmer line wound up between opposing pivots on each end of this. Difficult to describe but it works.

[Cuban8]

I did experiment with cutting my own foam cores years ago and was quite surprised at how well I could produce them with a little practice. I was using white polystyrene foam but what really put me off was the toxic fumes that were produced, that were not only unpleasant, but would give me a thumping headache after a short while. So.....make sure that you have excellent ventilation and take whatever steps you need to protect yourself. Never tried blue foam, but I suspect that the same applies.

Perhaps I was a particularly sensitive, but it was enough to get me to not bother continuing.

[Dave Hess]

I know some people use electric guitar strings, which obviously come in a range of sizes. A top E string can be .008 to .012 inches, a G-string will bedouble that and a B half-way between. You can buy them individually or in sets. If you buy a set,they go by the size of the top E string, then the rest increase in size in proportion, so they refer to the sets as 8s, 10s, 12s, etc.

**LINK**

[Former Member]

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[Roo Hawkins]

Hi I cut a lot of wings from 3 meters up to 7 meter span. I use a bow of 48in in length powered by one of them donut transforms can not remember what it is called but it has 2 25v out puts that can be made in to 50v. I only use 25v and go straight to the bow.I can control the temp by moving the wires closer together along the bow.the wire is from a old 1950s heater.

Edited By Roo Hawkins on 19/12/2018 10:58:36

[Roo Hawkins]

my foam cutter

[Nigel R]

"powered by one of them donut transforms can not remember what it is called "

That's a toroidal transormer Roo

For our purposes here, just the same as a standard brick shaped unit.

[Former Member]

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[Martin McIntosh]

That Spanish Windlass is what I was trying to describe above. Mine is virtually identical.

[Former Member]

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[eflightray]

Here's a tip.

Use your hot wire cutter to slice off thin sheets from the foam block ..... and then .......

build foam wings

Or just buy Depron.

Ray.

[kc]

If you only have one or two wings to cut rather than spend a lot of money on special wire and lab quality power supplies it might be cheaper to get them cut by a specialist such as BillKits (advert in BMFA mag usually)

But I use a bit of wire from an old electric fire element ( slightly sandpapered to remove any deposit ) and an old transformer from an old boiler. I adjust cutting speed instead of altering the voltage.

My tip is to avoid asking your wife to help hold the other end of the bow and ask an aeromodelling friend instead. It's easy to have a disagreement about the speed and therefore losing a friend is probably cheaper than a divorce.

Edited By kc on 19/12/2018 14:08:59

[John Duncker]

I used nichrome wire bought at the nats from SLEC MANY moons ago.

Power from a knackered 12 volt battery fed continiously by a 10 amp battery charger of the brainless variety. [ This is important otherwise you get voltage fluctuations as the brain varies the charger output..

On a 30 inch bow I used some extra wire and moved the connector along the extra to control the cutting wire heat. I had a bow with the tension produced by large elastic bands. This maintained tension as the wire lengthend on heating. I also had a 10 inch bow for small stuff that I could use one handed.

Much preferred working with urethane foam [ blue ]

Mostly used to build 12th scale combat and Zagi type wings.

[Former Member]

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[dave windymiller]

Posted by alex nicol on 18/12/2018 23:02:26:

Ive just been messing about with a home made foam cutter powered with a PC PSU controlled with a dimmer switch. I've tried various types of cutting wire from 0.27 - 0.6 nichrome wire ti lay straight control line wire. ideally I'm looking to cut a 30" span section.

Has anybody else tried this and if so what wire/PSU did you use

A PC power supply is switch mode type and powering it via a light dimmer which carves up the AC, sounds like a recipe for a distressed power supply! A dimmer would work much better on a simple transformer.

Ive had good results using guitar strings which is handy when you have a guitar too!

Cheers

Dave

[alex nicol]

Gents,

Thanks to all who took the time to respond. Your input great fully received. The PC PSU has been binned as it was struggling to cut 30" sections at full power and no dimmer switch.

I've tried various different wires and have settled for 0.5 dia nichrome. I'm on the look out for a suitable transformer I can use. In the meantime I found 15vdc tv/PC screen supply which I'd prefer to be a tad hotter, but I'm getting decent results just by slowing the cut down

[John Duncker]

Posted by David Mellor on 20/12/2018 09:20:23:

Posted by John Duncker on 20/12/2018 02:16:55:

Much preferred working with urethane foam [ blue ]

Are you sure it was urethane?? Blue foam, and pink foam, in sheets or blocks is usually extruded (as distinct from expanded) polystyrene, not urethane. Urethane foams don't cut with hot wire, as it tends to burn instead, releasing toxic fumes in the process.

No not sure at all. Some came from Sheffield insulation and some came from the skip at a building site. Mostly blue but some pink and some green.

It was closed cell and much finer than typical styrofoam.

It cut nicely and cleanly once I got the temp right.

I new the fumes were bad news so always had some positive ventilation going.

[Former Member]

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