View Full Version : Hot wire cutter: How do I make one?

Jonathan - n/a
31-Jul-08, 07:58 PM
In a spot of bother...

I'm trying to cut a 4'x2'x3" thick PU Foam, along the short side at an angle (about 30 degrees) so that It'll fit nicely against my planing surface.

<u>The Problem:</u> My Hacksaw only got me about 90mm before the handle got in the way, Trying to use the blade on its own failed within inches....

<u>The Solution:</u> (Apparently) is a Hotwire cutter,

However.... although I've used one (decades ago), I've never made one.

Can Anyone suggest how to ake a home-brewed one that won't either:

a) Give me a massive electric Shock or

b) Blow up the (mains/car battery)Power supply..

Thanks Jonathan

jon_curtis - n/a
31-Jul-08, 08:23 PM
stainless steel wire, i.e locking wire, but a thinner wire if you can find it would be better! dont think copper is any good.

current regulator and a car battery! you can buy current regulator modules from maplins, wood frame and off you go.

when i was young and building RC plans i used a car battery charger and guitar strings! but i wouldnt recommend using a mains power supply really!

you have to experiment with the amount of current supplied and the lenght of the wire!if you can't get heat with max current from your supply the wire is too long.

hoverchaps - n/a
31-Jul-08, 08:43 PM
Dont let health and safty know, but use a arc welder, you can hang a wire with a large weight from a celing, power with arc welder and jump leads only 32 volts.

jar2 - n/a
31-Jul-08, 08:48 PM
<font color="orangered"><font size="3">DO NOT HOT WIRE PU FOAM![/COLOR][/COLOR]

It releases lethal cyanide fumes when burnt!!

You can hot wire polystyrene foam if you are careful as Jon says but polyurethane is a no-no. If the foam is 3" thick then it may well be extruded polystyrene rather than PU. PU foam is normally light beige/cream in colour and slightly powdery when rubbed - extruded polystyrene is usually blue or pink/orange colour and has a non-crumbly surface

You can easily cut PU foam using a wood saw (fine pitch teeth are best but any saw will do).

Jonathan - n/a
31-Jul-08, 08:52 PM

I'd heard PU released fumes but figured the fume filters on my mask would deal with it, but cyanide.. http://hovercraft.org.uk/images/icons/smiley_icons/icon_eek.gif

I'll have a go with a wood saw....

JOSH -D - n/a
1-Aug-08, 07:22 PM
the fumes are just what the doctor ordered weren't they john http://hovercraft.org.uk/images/icons/smiley_icons/icon_lol.gif

Jonathan - n/a
5-Aug-08, 11:46 AM
Ok well I've got it cut!

I even managed to follow the basic rules http://hovercraft.org.uk/images/icons/smiley_icons/icon_eek.gif , you know the sort of thing: Measure everything twice then twice again before marking and then cutting.

I cut from both ends with the hacksaw to get the best finish over the greatest distance before switching to a brand new (I don't normally mess around with wood, prefer metalwork) fine toothed, extra rigid wood saw.

Quite happy with the End Result, the angle matched up against the planing surface pretty damn well, Even though the bits cut by the 'fine' woodsaw are rough and will need some expanding foam to make a good seal.

Only one teensy weensy problem....

I measured, marked and cut the wrong side http://hovercraft.org.uk/images/icons/smiley_icons/icon_redface.gif

I wanted to cut the 4'x2' into two equal 4'x1' lengths,

What I did was cut it into two 2'x2' lumps, ah well c'est la vie as Johnny foreigner puts it.

But I'm sure that It'll work, even it ifs not going to be as well finished/elegant as I'd liked.

This building large bits of your own craft is a STEEP learning curve.

Thanks to all who've helped so far, especially Tony Broad (you can tell he's a teacher, doesn't get mad even after the zillionth question) and Andy Collinss.