[ATM] Re: ATM Digest, Vol 11, Issue 15

[artbianconi@blast.net]

Mike, I have worked with Variacs for many years, most of them 
under the dangerously mistaken idea that because they were 
transformers they would thus insulate me from the amperage in 
120VAC line voltage.

That I did not kill myself is an act of good fortune, little else 
for my primary use was for hot wiring foam cores used in making 
aircraft wings and the device, which looks much like a cheese 
cutter, had a bare wire, that was heated from the Variac and thus 
exposed me to a shock potential.

Part of the mistaken assumption is in its designation as an "auto-
transformer" which deluded me into thinking it's a real 
transformer. It is NOT at all a transformer. It does not have an 
iron core nor does it share the familiar primary and secondary 
windings which a step down transformer normally includes and 
which do insulate the user from line voltage.

If your intention is to power an ac motor and adjust it's speed, 
you'd best be advised against that. The speed is fixed as is the 
RPM. Attempts to reduce the voltage will cause internal temps 
will eventually destroy the motor. DC motors are the ones best 
for regulating speed electrically but in the hp range needed to 
drive a polishing table, they are costly and you will still need 
pulleys to step the speed down further.

One experiment I have had some success with is using that same 
Hot Wire Saw design to build a small unit sufficient to cut nice 
straight channels in pitch for figuring the mirror. For safety 
sake, It still needs to be insulated by a conventional, 1 to 1 
transformer but you now can regulate the temp of the wire safely.

It's the fastest, most precise method I've used yet for grooving 
tools.

Art Bianconi 


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