Constructing a Foam or Plywood Bending Form

Basic info on building a solid form for gluing up curved laminations. February 14, 2010

I have been trying to find a different material other than MDF to create a large bending form for laminate bending. Any suggestions? I remember reading something about working with construction foam, but cannot find the post and since I don't have any experience with building houses and materials used I don't even know what this construction foam would be. Please share if you have any ideas.

Forum Responses
(Furniture Making Forum)
From contributor J:
You can make plywood ribs and skin it in bending plywood. I space the ribs about 4" apart, and put spacers in between them. Owens Corning Pink insulation is the foam you're looking for. It comes 2" thick. If you need thicker than that there is special adhesive for it, otherwise it melts. I think it works well for forms that won’t be used too often.

From contributor M:
Yeah, I've considered foam for one-off forms. I think it goes like this: laminate a block of pink board (without backing) together. Cut two 1/4 MDF form shapes. Glue these to either end of the foam block. Trim the block to shape with a tensioned hot wire guiding against the two MDF shapes. A Google search on building a hot-wire foam cutter would probably prove valuable. This is my understanding, but perhaps someone who has actually done this will chime in here in a bit.

From contributor O:
I've actually done it. The trickiest part is building the hot wire cutter. It took me an afternoon of Googling and reading to understand enough about electrical resistance to build the cutter. For the sake of safety wire cutters are generally made to run at low voltage (12-24V), which means you need a transformer to power it. I used a 12 volt, 6 amp car battery charger that was powerful enough to heat a wire about three and a half feet long to foam-cutting temperature. A longer wire would require a bigger transformer. Also, I used water-based contact cement to laminate the foam block together. It was important to use the vacuum press for the foam lamination, to be sure that the pieces were firmly pressed together before they're cut to shape. Email me if you want details.