Hot-wire cutter

My hot-wire driver is simple. I bought a 2KVA variac (from ebay $100) which I can use for other things (love tools, of course) and a used Signal 600VA 25A 24V transformer (again from ebay $70). It has plenty of taps but I just took the 0 - 24V which will give me 25A capacity. Alternatives are two parallel 12V @ 50A if needed. Simple battery clips for attachment of the old recycled speaker wire. I am going to switch these out for real crocodile clips though. Smaller and better grip on small wire.

The tools are simple too. I did some of the cutting with some stainless MIG wire at 0.045. I then bought some nichrome 21ga (0.028) which makes a better cut, smaller kerf and with tension can be pulled much straighter. The ribbon is 3/16" x 0.018. I bought the wire and ribbon from M-pak Systems although I had to get 10' minimum of the ribbon - I did find other places selling similar ribbon by the foot.

For making the bellmouth cut it required about 35VAC out of the variac - translating to 6VAC from the transformer. The ribbon seemed to act very much like the wire in terms of volts it took to heat it. I did try to cut a bit colder (just enough heat to cut - but slowly) as I worried aoout the radiant heat from it's width could cause melt outs. I might experient more with offcuts to see if there's a good speed/temp to use - although what I did with the bellmouth worked well except where there was very thin foam to cut off (almost none).

One thing I found interesting about the nichrome is how its resistance must change with heat. It would have surges where it would be just getting a little too hot (glowing) but still fine then all of a sudden it would be bright red and snaps. I did not get this with the stainless wire. Anyways it only really happened if I was not paying attention.