Cutting Sponge - UK Vintage Radio Repair and Restoration Discussion Forum

howard · 24th Sep 2006, 12:21 pm

Hello,

I often have to cut new bits of sponge to replace pieces in radio battery compartments which have disintegrated and I find that cutting sponge with scissors always seems to leave an untidy or crooked edge. Car upholstery restorers use a hot wire tool to cut through replacement sponges for seats etc so I've now tried heating up a piece of fusewire over a gas hob and then immediately plunging it through a piece of sponge and it leaves a perfect straight edge

One has to be very quick though cos the wire cools down very quickly

I guess there may be a better way of heating up the wire so that one can take one's time .......... any suggestions ?

Howard

Station X · 24th Sep 2006, 12:29 pm

A thin piece of wire will always lose heat quickly, so it needs to be constantly heated.

You could use a piece of wire taken from an electric fire element. Use 1/20th of the total length and a 12V car battery or pro rata.

You'll need a suitable frame such as that from a plastic tilecutting saw. Pieces of metal will be needed at each end of the wire to stop it melting the frame.

Nickthedentist · 24th Sep 2006, 12:29 pm

The classic way of doing this is by passing a controlled current through the wire to keep it hot.

Some of the "schools" suppliers [Maplin? Rapid?] used to sell a hacksaw-like frame with special wire for this very purpose.

Googling is informative, e.g. this one using a soldering gun to provide the current: http://club.cycom.co.uk/hotwire/Hot_...rene_foam.html

Nick.

P.S. I see Graham beat me to it!

Chris_C · 24th Sep 2006, 6:58 pm

Please be aware that hot cutting some plastics inc. some foams can give off unpleasant gasses.

So do it near an open window or door

mikelect · 24th Sep 2006, 9:38 pm

Hi Guys, "THE" tool for cutting foam rubber is an electric carving knife

I've used one for years for this purpose and it's truly excellent, if you can't persuede SWMBO to part with hers, scour the boot sales there is always plenty about

Mike

GJR 11L · 24th Sep 2006, 10:05 pm

I made my own tool from a block of aluminium for cutting the round battery pads for fitment to the inside of the back covers on Hackers, I place the foam on a block of wood, then just press on the tool by hand, picture of it here, but it's obviously no use for cutting square bits!

ppppenguin · 24th Sep 2006, 10:11 pm

I've used an ordinary carving knife or bread knife to cut thick sponge. Don't know if it would work so well on thin or very low low density sponge. Maybe not as easy as an electric carving knife but I don't have one so I can't really say.

Many years ago I used wire from an old heater element to cut large sheets of expanded polystyrene. Wire was about 5' long with a handle on each end. Obviously a 2 person job. We used some kind of variable power supply to heat up the wire. Worked very well though the smell was horrible.

Mike Phelan · 25th Sep 2006, 8:37 am

There used to be a device with a hot wire that was mounted on a large 15.v cell - the ones used as a gas lighter (remember them?)
It did look a bit like a hacksaw frame.

Sideband · 25th Sep 2006, 11:24 am

I'm sure I've seen something in B&Q that was designed for cutting polystyrene foam. It was in the shape of a soldering gun with a wire between the two poles and a large battery.

Maybe these no longer comply to the current safety laws!

Rich.

wireless_paul · 25th Sep 2006, 11:50 am

Quote:

Originally Posted by ppppenguin

I've used an ordinary carving knife or bread knife to cut thick sponge. Don't know if it would work so well on thin or very low low density sponge. Maybe not as easy as an electric carving knife but I don't have one so I can't really say.

Many years ago I used wire from an old heater element to cut large sheets of expanded polystyrene. Wire was about 5' long with a handle on each end. Obviously a 2 person job. We used some kind of variable power supply to heat up the wire. Worked very well though the smell was horrible.

I have just tried the electric carving knife method and it works OK, although I think a normal sharp carving knife which I have used in the past probably works just as well.
Paul

Mike Phelan · 25th Sep 2006, 4:41 pm

Quote:

Originally Posted by Mike Phelan

There used to be a device with a hot wire that was mounted on a large 15.v cell

That, of course, should have been 1.5 volt

PJL · 25th Sep 2006, 4:56 pm

The cuttter was used in aero-modeling, I had one when I was a youth many years ago. I hope this link is permitted http://cgi.ebay.co.uk/Polystyrene-Fo...QQcmdZViewItem. May not be hot enough for foam.

Andy Day · 23rd Oct 2006, 8:43 pm

I've watched professional upholsterers cut foam, and they use a gadget like an electric meat carver. No fumes, and a clean edge. then they sand the profile with a rotary disk akin to the thing you would use to prepare a bit of rusty metal for priming. But maybe a bit finer?

24th Sep 2006, 12:21 pm	#1
howard Nonode Join Date: May 2005 Location: Godalming, Surrey, UK. Posts: 2,593	Cutting Sponge Hello, I often have to cut new bits of sponge to replace pieces in radio battery compartments which have disintegrated and I find that cutting sponge with scissors always seems to leave an untidy or crooked edge. Car upholstery restorers use a hot wire tool to cut through replacement sponges for seats etc so I've now tried heating up a piece of fusewire over a gas hob and then immediately plunging it through a piece of sponge and it leaves a perfect straight edge One has to be very quick though cos the wire cools down very quickly I guess there may be a better way of heating up the wire so that one can take one's time .......... any suggestions ? Howard

24th Sep 2006, 12:29 pm	#2
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: Cutting Sponge A thin piece of wire will always lose heat quickly, so it needs to be constantly heated. You could use a piece of wire taken from an electric fire element. Use 1/20th of the total length and a 12V car battery or pro rata. You'll need a suitable frame such as that from a plastic tilecutting saw. Pieces of metal will be needed at each end of the wire to stop it melting the frame. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

24th Sep 2006, 12:29 pm	#3
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,859	Re: Cutting Sponge The classic way of doing this is by passing a controlled current through the wire to keep it hot. Some of the "schools" suppliers [Maplin? Rapid?] used to sell a hacksaw-like frame with special wire for this very purpose. Googling is informative, e.g. this one using a soldering gun to provide the current: http://club.cycom.co.uk/hotwire/Hot_...rene_foam.html Nick. P.S. I see Graham beat me to it!

24th Sep 2006, 6:58 pm	#4
Chris_C Hexode Join Date: Jan 2003 Location: Darlington (DL3) North East U.K. Posts: 394	Re: Cutting Sponge Please be aware that hot cutting some plastics inc. some foams can give off unpleasant gasses. So do it near an open window or door __________________ Chris C G8TJR

24th Sep 2006, 9:38 pm	#5
mikelect Retired Dormant Member Join Date: Sep 2003 Location: Wrexham, North Wales, UK. Posts: 799	Re: Cutting Sponge Hi Guys, "THE" tool for cutting foam rubber is an electric carving knife I've used one for years for this purpose and it's truly excellent, if you can't persuede SWMBO to part with hers, scour the boot sales there is always plenty about Mike

24th Sep 2006, 10:05 pm	#6
GJR 11L Heptode Join Date: May 2004 Location: Ellington, Northumberland, UK. Posts: 815	Re: Cutting Sponge I made my own tool from a block of aluminium for cutting the round battery pads for fitment to the inside of the back covers on Hackers, I place the foam on a block of wood, then just press on the tool by hand, picture of it here, but it's obviously no use for cutting square bits! Attached Thumbnails __________________ John.

24th Sep 2006, 10:11 pm	#7
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Cutting Sponge I've used an ordinary carving knife or bread knife to cut thick sponge. Don't know if it would work so well on thin or very low low density sponge. Maybe not as easy as an electric carving knife but I don't have one so I can't really say. Many years ago I used wire from an old heater element to cut large sheets of expanded polystyrene. Wire was about 5' long with a handle on each end. Obviously a 2 person job. We used some kind of variable power supply to heat up the wire. Worked very well though the smell was horrible.

25th Sep 2006, 8:37 am	#8
Mike Phelan Dekatron Join Date: Nov 2003 Location: Near Leeds, West Yorkshire, UK Posts: 4,609	Re: Cutting Sponge There used to be a device with a hot wire that was mounted on a large 15.v cell - the ones used as a gas lighter (remember them?) It did look a bit like a hacksaw frame. __________________ Mike.

25th Sep 2006, 11:24 am	#9
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,577	Re: Cutting Sponge I'm sure I've seen something in B&Q that was designed for cutting polystyrene foam. It was in the shape of a soldering gun with a wire between the two poles and a large battery. Maybe these no longer comply to the current safety laws! Rich. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

25th Sep 2006, 4:56 pm	#12
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Cutting Sponge The cuttter was used in aero-modeling, I had one when I was a youth many years ago. I hope this link is permitted http://cgi.ebay.co.uk/Polystyrene-Fo...QQcmdZViewItem. May not be hot enough for foam.

23rd Oct 2006, 8:43 pm	#13
Andy Day Pentode Join Date: Aug 2005 Location: Hemel Hempstead, Hertfordshire, UK. Posts: 154	Re: Cutting Sponge I've watched professional upholsterers cut foam, and they use a gadget like an electric meat carver. No fumes, and a clean edge. then they sand the profile with a rotary disk akin to the thing you would use to prepare a bit of rusty metal for priming. But maybe a bit finer? __________________ The older I get, the faster I was!