Hot Wire Foam Cutter

[Bernd]

If any of you have read my Air Boat thread you saw that I have a nitro powered speed boat. Great fun until the engine dies way out in the water. I plan to remedy that by building a twin electric motored rescue boat. It will have two pontoons on it made from sytrofoam that will be covered with a layer of fiberglass. But in order to shape the styrofoam so that you get nice edges one needs a hotwire styrofoam cutter and that's what I built.

The whole write up is on my web site at http://www.kingstonemodeleng.com/MachineShop/foamcutter/foamcutter.htm. I'll touch on the high lights here. If your interested in building one the details are on web site.

The table is made from a piece of tread mill. The wood is MDF and coated with some kind of plastic. Nice for the foam to slide on.



I built up an overhead arm out of wood and attached 1" aluminum angle plates.



The wire is .015" thick nichrome wire about 20 to 24 inches long. It is attached with home made fastners.



The power supply is out of a computer. I'm using the 12 volt supply. Here's it what it looks like cutting the foam.



And the cut pieces. Nice and smooth.



Later I found a 15 volt DC power supply and tried that. Works even better. Here's the temporary set up.



I use the aligator clip on the wire to adjust how hot the wire gets by moving the clip up and down on the wire. This set up will work for the rescue boat project. Later I plan to make this a bit more permanent.

Regards,
Bernd

[andyf]

Berndt, how do you stop the molten edges of the foam welding itself back togeher again once the hot wire has passed through? When I tried it, using wire stripped out of an old hairdrier, it sealed up again behind the cut

Andy

[dsquire]

Bernd

Great project. This is something that a lot of modellers could have a use for. Both boats and airplanes. I know that some of the guys that fly on floats can't come out unless someone comes with a boat for retrival purposes.

Cheers 

Don

[Bernd]

Andy,

It never glues itself back together again. Could be your wire might be to hot. It should just be hot enough to cut through the foam. I'm sure different types of foam will probably melt at differrent temps. The blue foam that I'm using doesn't seem to melt back together. I tried some white foam such as used for boxes and there was some melting back together.

Guess I'll need to experiment and see what the different colors of foam do.

Bernd

[Bernd]

Don,

I've seen many types of foam cutters on web sites but never any explination as to how they were assembeled or what they used and how. I also know that each situtation is different.

I first came into contact with very large cutters from the guys that built there own hovercrafts. I've got plans to build a 2 person craft. Another project I'll probably never get to.

I realize that each project is unique and will need it's own foam cutter design.

Any way now I can get on and start with the 2 pontoons. I'll be starting a thread on building the rescue boat next.

Bernd

[dsquire]

Bernd

The temperature and the speed of the hot wire is the most important thing. In theory, the hotter the wire the faster the cut. The idea is that the wire does not cut the foam, it just melts it when it gets close to it and when it cools pulls back to each side and is more dense at the 2 cut surfaces. In theory the wire should not even touch the foam. It just gets close to it and melts the foam as it goes. Too fast and the wire hits the foam before it melts it. Too slow and it melts too much causing an uneven cut and possible closing up behind the wire.

This is why the temperature and the speed are so important. The best thing that one can do is practice, practice and some more practice. Now having got that all straight, it is different cutting through 2" thick foam then it is to cut an airfoil shape 30" long. Did I say more practice.

All that styrofoam and blue or pink foam that you see out on garbage pickup day, take it home with you. It can be cut up into useful pieces once you get the hang of it and until then is cheap for practice.

Some place on one of my computers I think I have alink to some hot wire information. If I can find it I will post it up here for you.


Links added:

Here are a couple of links that may give you a few ideas. Also have some CNC controled hot wire cutter links if you are interesterd.

http://www.rcgroups.com/forums/showthread.php?t=628704&pp=30

http://www.8linx.com/

http://www.utahflyers.org/index.php?option=com_content&task=view&id=37&Itemid=33


more links added 2009-09-30

bit of foam cutting and lots of metal casting info
http://www.abymc.com/

commercial foam cutting machines
http://www.foamlinx.com/

Foam cutting power supply
http://nsrca.us/all/building/65-powersupply.html

 
Cheers  

Don

added links September 29, 2009, 10:39:06 pm
added links September 30, 2009, 12:13:06 pm

[Bernd]

Don,

Ain't that the truth, pratice, practice, practice, repeat as needed.  

I have a bunch of foam from when they built the house, so don't need to dumspter dive just yet.

What is the best glue for gluing two pieces together. I've tried several products. The spray adhesive seemed to work the best. I then need to cover with fiberglass. I did a test piece with "Atomotive Fiberglass Resin", "Finish Coat" and succeeded to melt the foam. I guess there's several different resins out there. One of them must be compatible with the foam? Any idea's? Thanks.

Bernd

Edited: Yeh, add as many links as you can find. Would be nice to get them all together in one place.

[dsquire]

Bernd

I have always used a slow setting epoxy when joining foam. I have also used a water based contact cement to glue two sheets together or to add a veneer covering. Atomotive Fiberglass Resin will attack most foam so must be avoided. If you want to cover foam with fiberglass cloth for strength then I would check out West Systems Epoxy. You can adjust the working times and it is one of the safer epoxies to use if you have adequate ventilation. Here is their link.
http://www.westsystem.com/ss/

I have never used it personallly but have followed a lot of articles that used it and read up on it quite a bit. It is the epoxy that I would be using if I needed a quart or more or was building a mould and parts. From everything that I have seen they seem to have an excellent reputation in the boat building community.

I also added a few more links earlier today in the above post. I figured that way they would all be together instead of spread out.

This afternoon while house cleaning I came accross some extra foam so we loaded up my delivery mans' vehicle and I gave him direction on how to get to your place so please keep an eye out for him. If there is more than there than what you can use, maybe you can give him directions to Andys' place and he can have the rest.


Cheers 

Don

[Bernd]

Don,

After checking those links you posted I've gotten a bit smarter about all that's been talked about. The Utah Fleyers had the best info on building hot wire cutters. Didn't know that many kinds exsisted.

Also remembered from my days on a hovercraft forum. They taked about the West System. I checked out the prices and downloaded the price sheet. Looks like close to $75 for the intial setup. I think I'm going to try that out. There are several places close by that sell the stuff.

I think I've come to a final design on my rescue boat. I built one foam pontoon to try out some ideas. Looks like I'm going to go with two electric motors using airplane props to push it. Reason being is nothing can get caught, like sea weed, on the prop or rudder. Simple 2 channel radio and a couple of 6 volt batteries for the motors.

I see some foam I can use on that delivery guy. Then I'll send him to Andy. 

BTW, those links are great.

Bernd

[Stefan Pynappels]

I built a very simple hot wire cutter when I worked as a lab tech in a college and I was asked to come up with a way of cutting polystyrene sheets abot 30mm thick into jigsaw like shapes which were supposed to simulate enzymes locking together or something.

2 thin wooden beams on either end of a pivot block with screws in the ends to connect the nichrome wire to. There was only 60mm of wire, but the throat of the cutter was about 600mm. I used a variable power pack from the lab to power it, and at the end of cutting out 400 shapes, I think I got the knack of adjusting speed and current to get clean cuts. Still hate the smell of it though..... and I think they still use my ridiculously simple bit of kit now.

[andyf]

Yeah, Berndt. Turn him upside down so he doesn't drown, and chuck him in the Atlantic - the westerlies should soon blow him over here 

For interest, here's the freehand foamcutter I made to avoid getting polystyrene granules everywhere when cutting up slabs of the stuff to insulate my shop. Made of bits of PCB and hairdrier heater, tensioned by my forefinger on the PCB "trigger". It worked quite well, but only in straightish lines, because of the thin metal riving blade which helped prevent the foam sealing up again behind the wire.

 

Andy

[jatt]

Might have to give the hot wire a go on some soft foam.

Most of the time I just use an electric knife.  Unfortunately the thicker stuff really taxes the motor.  Waiting for it to let the smoke out. 

Fortunately I dont have to contend with bits of polysytrene going everywhere.

[Bernd]

If your going to build one attach the wire on one end to a spring or counter weight to keep the wire taunt (stretched) or it won't cut perfectley.

I'm going to modify mine when I'm done with the boat.

Bernd

[PTsideshow]

Might have to give the hot wire a go on some soft foam.

Most of the time I just use an electric knife.  Unfortunately the thicker stuff really taxes the motor.  Waiting for it to let the smoke out. 

Fortunately I dont have to contend with bits of polysytrene going everywhere.

Do not use an electric hot wire cutter on upholstery Foam rubber as very toxic fumes are released Having built foam rubber clown props for close to 30 years. That is the fastest was to get a trip to the emergency room.

And most doctors will not think to ask a bout cutting seat cushion foam with a hot wire cutter.
had a couple of teenagers that were to smart to listen to me at a magic shop I supplied. one was in a coma and the other was very close.

Head aches and nose bleeds are two of the symptoms, so if you do make sure that a loved one or pin a note to your chest so they know what to treat you for.

I know they have changed the formula to remove the toxic agents, I but some people use used cushions. And don't know the age of the foam.

[PTsideshow]

He's a video from MIT on using the dock building high density foam and hot wire cutter.
video is a little choppy as it reloads.
http://techtv.mit.edu/videos/2175-learning-to-cut-blue-foam-with-dave-wallace
It is 14 minutes long.