# Turning foam on a lathe?



## Bulldogg629 (Apr 5, 2011)

I want to turn a vase using the profile of a face, its easier for me to post a pic than explain it. Im going to either cast it in cement or cover it in fiberglass, either way I need to start with a foam form. For this try I made a block by gluing several layers of 1.5” insulating foam together with a dowel in their center. Figuring that foam would be easy to cut I made a cutting tool for the entire profile out of ¼” ply with the edge sanded sharp and soaked in super glue to harden it and figure I would just use that to scrape the foam. As you can see in the photo I ran into a few problems. My wooden cutting tool makes a very rough surface. Whats a better way to do it? I don’t really have the tools or talent to make the same cutting profile out of steel. My bigger problem was that as the diameter turned down smaller and the layers had less surface attaching each other, they let go. I considered instead spraying some of that canned expanding foam into a 5 gallon bucket and them poping it out, that might give me a solid foam blank. Any ideas on better ways to go about this whole process? Thanks


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## Admin (Feb 13, 2012)

Research on the net "hot wire foam cutting", this will tell you what you need to make one then simply mould your wire to the profile you need. Fabricate to simple "book end" centres, one end with a simple crank handle for turning and away you go. Experiment first with some scrap, it will take a little trial and error to get the correct wire temperature and turning speed.
I have a friend who did this to create the various components for his hover craft then fibre glassed it. Worked perfectly


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## OPG3 (Jan 9, 2011)

I have seen and used quite a few products that were cut using a "hotwire" method - but have personally never seen that used to work on a lathe turning - only stuff rotating much slower than a lathe. It might be that it could be mounted in a lathe and rotated without the power assist of the lathe's motor.

I have never done such a thing as you have described, but would venture to guess that careful use of 1" wide sanding strips would be a good thing to try. Insulating foams go away quickly when encounted with anything abrasive. Also, have you tried the Surform tool or a rotary rasp or a hand-held MicroPlane?


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## Bulldogg629 (Apr 5, 2011)

I have considered the hotwire method but saw some problems with it. On the hotwires Ive seen, the wire is pulled tight on the bow. You wouldnt be able to pull tight a wire that had a shape bent into it without pulling the shape out, and if you used a wire heavy enough to hold its shape and not sag would you be able to run enough electricity through it to make it hot enough? Im also not sure if I would be able to bend that shape into wire and have it look as nice as I'd like. As for the bookend idea, that would be easy enough, I could just leave it on the lathe and rotate the lathe by hand afterall. But if I could figure out the problems on that, it certainly would make the nicest cut and would cut the entire thing out in 1 rotation of the work.


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## Gaffboat (Mar 11, 2012)

Here's an example of a 3D foam lathe from Hotwire Foam Factory. (3D Pro 16-Inch Table Kit) You can see that the wire can be bent to the shape you need and the table rotates by hand. Hot wire cutting gives the cleanest cut. Most other tools just break off chunks of foam. That method is good for getting rid of lots of foam fast, but not so good for detail. I have used a small version hot wire cutter and it is neat and fast.


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## Gaffboat (Mar 11, 2012)

Bulldogg629 said:


> I considered instead spraying some of that canned expanding foam into a 5 gallon bucket and them poping it out, that might give me a solid foam blank. Any ideas on better ways to go about this whole process? Thanks


Just another question and thought: Are you trying to make these in quantity? If so you could make the original out wood or whatever, make a mold, and then produce them by casting in resin or two-part foam like they use to produce movie props. Check out BITY Mold Supply - Mold Making, Mold Rubber and Casting Resins | Home


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## markristow (May 30, 2011)

Try glueing the foam up parallel to the centre dowel, then you won't have to worry about the joins. As far as the tool goes, I think if you wrapped some sand paper around a dowel ( about 60 ar 80 grit will do) this would work better.


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## Bulldogg629 (Apr 5, 2011)

No this is a one off project so no need for molds. Ive been reading about hotwire cutters as well. I figured I could use some farmers wire to bend the shape, assuming I could bend it into the silhouette with enough detail. But from what Ive read on making a hotwire is that your transformer has to match the needs of your wire properly or else you burn it out. And for what little I know, I know that the type of wire, diameter of it, and length, all affect its resistance but I dont know how I would test it to figure out what I need and smoking $10 transformers would add up fast. It seems like a nice way to cut, but a lot of work for the size of the project. But I wont rule it out. Something else Ive considered is epoxying nails to the side of my wood template, lining all the points up along the edge to make sort of teeth for cutting.


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## CharleyL (Feb 28, 2009)

A Dremel Tool or 1/8" air die grinder and some wood carving bits should do this well. Run the lathe slow and use the spinning bit as your cutting tool. See this link Bits for an example. The Saburr type bits are great for roughing. Then a coarse or medium diamond bit for the finish cut. You may need to do some fine finish sanding by hand, but it should turn out to be as smooth as the bubbles in the foam will allow.

We do a lot of foam carving for museum exhibits, but not very much on work that is this small and none has ever been done on a lathe. On these large carvings, the rough shape is usually done with whatever works. The crudest tool is a right angle grinder with a flat metal disk with bolts sticking out to act as spinning fingers. It is very crude, a bit unsafe, and very messy, but it gets the job done. An electric chain saw is also used. Some of these carvings can be 8' high and 12' long so there can be a lot of foam to shape. The foam is usually white styrofoam or the pink insulation foam in thick planks that are glued together to achieve the desired block size. Smaller sanders and power carving tools are then used to achieve the finished surface and fine details. The completed carving is then sealed and painted. or sometimes fiberglass covered, depending on it's end use and life requirements. 

Charley


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## papasombre (Sep 22, 2011)

Hi, Oliver.

Is this another ACME product fron your shop?

Looks very nice.


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