I use my Powerlab 8 to cut my cores. I adjust the amperage depending on what I'm cutting and the length of my bow.

Do a couple of cuts to get the temp right, then have at it.

MM,

I use an EKI full wave speed controller.  You can buy the kit and
assemble it yourself ($ 14.49 ).  It can handle any length of wire, since
it has a potentiometer. it is, of course, a lot less money than a variac.
Longer wire, more voltage for the same temperature.

EKI link :  https://abra-electronics.com/educational-kits/motor-and-stepper-motor-kits/eki-2062-full-wave-motor-speed-control-kit-eki-2062.html?sl=en

These kits were developed as electronics education projects : Potentiometer, 2 capacitors, resistor, 2 diodes, 2 neon bulbs, 2 SCRs, slide switch, outlet, line cord.  Also includes the circuit board. You should make an enclosure for safe operation.

In order to compensate for the expansion of the wire ( min is 48" long), I put a screen door spring at on end of the wire so that the reduction in tension
is minimal.

Rex

My main problem is I don't know where to buy foam and nobody seems to want to give up their source.

 Look for a place that sells "refractory materials" and ask for 1 pound virgin foam.  Bob Hunt can tell you where to get it in your neighborhood.

Well, actually the foam billets I purchase are quite a bit bigger than a volkswagon... In fact, they come out of the mold measuring 37 inches by 48 inches by 16 feet! They are virgin bead EPS (Expanded Polystyrene) at 1 pound per cubic foot density. I might consider selling sheets of foam, but the mailing cost for a sheet would be prohibitive.

No matter where you get your foam, specify virgin bead; if there is any regrind in the billet the wire will hang up on the solid bits of regrind and ruin the cut. Don't ask me how I know this...

There is a learning curve to cutting foam, and you will blow a few panels until you get the knack.

Later - Bob

Your a Jersey man.  Here's where I get my foam for wings.  Ask for 1 pound virgin foam.  I get blocks cut  2", 3" and 4" thick.  Each block measures 38" x 48 1/2".  I go pick it up, so no shipping cost except for my gas and time.  I usually buy 8 to 10 blocks at a time.  Not cheap but I think they are reasonable.

Foam Pack Industries
72 Fadden Road
Springfield, NJ

973-376-3700

Build a kit? my charger can do it. My main problem is I don't know where to buy foam and nobody seems to want to give up their source.
MM

Motorman,

     It's really a dilemma with me; to buy a kit or to buy an ARF. Thanks to folks responding your post, I know that
the light dimmer is a true option and that it is CHEAPER than the EKI kit. So, if the ARF is cheaper (and probably more
robust), the ARF is the only option.

    Fate was with me yesterday as my trusty EKI unit gave up the ghost yesterday and I actually went to HD and bought
a $ 4.95 light dimmer.

     I always have an incandescent light bulb in parallel with the nichrome wire so that I can respond to changes
in voltage of the supply output. When the air compressor started, the voltage dropped and the wire cooled without
returning to temp when the compressor stopped. This probably caused by the weird properties of either the nichrome
or the control that make the circuit resistance an inverse function of wire temp.

     However you power the cutter, I suggest you monitor voltage across the wire to be able to respond to changes. I'm
sure a refrigerator starting on the circuit could do the same thing.

Motorman,

     It's really a dilemma with me; to buy a kit or to buy an ARF. Thanks to folks responding your post, I know that
the light dimmer is a true option and that it is CHEAPER than the EKI kit. So, if the ARF is cheaper (and probably more
robust), the ARF is the only option.

    Fate was with me yesterday as my trusty EKI unit gave up the ghost yesterday and I actually went to HD and bought
a $ 4.95 light dimmer.

     I always have an incandescent light bulb in parallel with the nichrome wire so that I can respond to changes
in voltage of the supply output. When the air compressor started, the voltage dropped and the wire cooled without
returning to temp when the compressor stopped. This probably caused by the weird properties of either the nichrome
or the control that make the circuit resistance an inverse function of wire temp.

     However you power the cutter, I suggest you monitor voltage across the wire to be able to respond to changes. I'm
sure a refrigerator starting on the circuit could do the same thing.

I would be concerned with the shop wiring or the compressor start capacitor if-- as the compressor is running--- the shop voltage drop was that noticeable on a hot wire bow

I have a very complicated primary supply to the house and three external shops (2 of which are on a separate meter but common transformer)

If the house AC soft starts or the air compressor kick on, or I fire up the high amp table saw and dust collector I can sag the AC voltage only during the start time and then back to full AC voltage

Then again my son is a master electrician who designed all my shop service and used the proper sized wiring and breaker panels.

If you think your wiring is proper I would suspect the compressor start capacitor is weak and need replacing

Start popping panels, checking wire size, and tighten everything.  It is pretty amazing how loose wire fittings get after a few years, even properly sized stuff will heat up enough to loosen!  (even at the outlets)

If there is under size wire, then pull another circuit.  Either remove the old circuit, cut it back abandoned, or breaker it for the draw it is allowed to take and use the circuit accordingly.

Other than the mains this is an easy job that is safe to do after turning off the mains. 

Phil