So I agonized over hot wire foam cutters for a couple of weeks, and made a functional straight wire cutter, but couldn't get a low enough voltage at high enough current to drive my "router table" rabet/dado cutter.
I ended up cutting my foam with a very sharp, very thin kitchen knife. It produces very little "foam chips" and leaves almost as smooth an edge as the hot wire. The knife is an 8" filleting (boning) knife that is very thin and flexible.
And it turned out to be about 1000X less work than setting up and adjusting the fence on the hot wire cutter for each piece I had to cut.
I have finished cutting and dry-fitting all the foam panels (1" rigid styrofoam insulation) in less time than I spent screwing around with the hot-wire cutter.
My friend says that I over-think and over-engineer things. She's right, and here is a good example. I spent less time cutting the 10 pieces with a kitchen knife than I spent just trying to get the hot-wire cutter working.
My advice: don't overlook the simplest solution.
<Chas>