On Sat, 06 Nov 2010 22:19:02 -0700, Bill Noble
wrote:

On 11/6/2010 9:00 PM, wrote:
On Sat, 06 Nov 2010 13:44:23 -0700, Rich Grise
wrote:

Winston wrote:


Aw, gawrsh, 'tweren't nothin'. ;-)

Thanks!
Rich
Variacs are MUCH more to be preferred (reccomended) for the job.

at the risk of being hostile, "nonsense" - variacs are NOT to be
preferred, unless you have no clue about electronics and are unwilling
to purchase a suitable thyrsitor or SCR controller. The variac is
larger, more prone to physical dammage, they wear out, and they are not
a regulating supply, a simple triac controller can hold constant
voltage at the output and avoid the inductive transients by switching at
zero crossing, or by using higher rated parts. Your statements are
wrong, the controllers that do this job are available for a few dollars
(go to harbor freight and buy a "router speed control" when it's on
sale) and have been common for a few decades.

A variac does have its uses, particularly if distortions of the AC
waveform are undesireable, but this is not one of them
I was not talking about specialized thyrister controllers - I was
talking about "lamp dimmers" - and I am not electronically
illiterate. The one advantage I have found with variacs is they are
linear in response, and rcontrol smoothly from virtually ZERO to full
(or even higher than full) voltage.
MOST thyrister controllers - even specialized ones for motor control,
have a somewhat limitted control range. Many will not control to below
approxemately 5%.
That is not an issue in this application since with a stepdown
isolating transformer in the mix the control range would be quite
narrow anyway.

Yes, specialized controllers will do the job, and do it well - but
last time I priced a 600 watt magnetically rated Lutron it was over
$69, and I've picked up numerous used and surplus Variacs, from 0.5 to
2.5 kva for under $20 each.

Most of the amateur built (in the USA they call then experimental)
plane builders I know who have used hot wire cutters have used
Variacs. Myself, I'm building with ChroMo steel and 6061T6 Al.