(1) My hot wire cutter was built from 3/16″ aluminum sheet only because that’s what I had on hand, but having it attached to the table saw is prefect because I can use the fence and push guide as well as tilt the wire if needed.
(2) The saw blade is removed and the wire cutter is bolted onto the back of the spindle bracket where the safety guard normally goes.
(3) (4) I tested a battery charger as a power supply for heating up a cutting wire, but this was not successful as the charger apparently had a shutoff built in to keep it from overheating due to a complete short. So I found a regular transformer from American Science Surplus at www.sciplus.com that will output 7 amps at 24 volts AC. The transformer gets its power through a dimmer switch so the voltage on the wire can be reduced. One end of the power from the transformer actually is grounded most of the time because the wire lightly touches the blade guard, but the top end is isolated with a piece of plastic tubing that is glued onto the aluminum frame with epoxy. The wire is pinched between a couple of washers on a 1/8 inch bold. The small bolt is nice it can be bent if needed in order to get the wire at 90 degrees to the table.
(5) For slicing wide pieces of foam a plate of aluminum with an L shape bracket welded to the backside is clamped to the existing table saw fence.
You can buy Nichrome wire but steel guitar strings (not the wound kind) work great. Note that Nichrome is a brand name. What you are really looking for is “resistance wire”. Others user fishing leader wire like the Stainless Steel Single Strand Leader Wire, 69lb. .018 Diameter made by Mason Tackle. Since my transformer outputs 7 amps at 24 volts I can also use .035 welding wire, but it is harder to control and much less accurate than the smaller wire. However, the welding wire can be bent into desired shapes, and when duct taped onto a piece of wood for a handle or mounted on a turn table or table saw it can be used like a router or shaper.
I since purchased a 1/4 pound spool of .01 diameter stainless steel wire from www.McMaster.com because I was going through too many $1.50 guitar strings.
(6) I also made a handy hand held wire cutter. The plastic clamp holds a steel rod which supports on end of the stainless steel wire as well as one side of the electrical connection from the transformer. A small bolt treaded through one jaw of the clamp holds provided a connection for the other wire from the transformer and the other end of the stainless steel wire. The wire slacks when it get hot, but that is not a problem when cutting out items using a pattern. A small block of wood can be inserted between the steel rod and wire in order to shorten the cutting area. (7) In the photo the cutter has been used to core out 4 1/2 inches of foam between to parts of the jet pump in order to make an extension.