stacking variacs

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Original poster: DRIEBEN-at-midsouth.rr-dot-com 

Hi all,

I recently obtained another 1156 style variac to series with my
5000 watt rated Luxtrol. They have identical 1156/1256 type Power-
stat frames so they match right up for placement of a common shaft.
The problem that I'm having is when I try to tighten the nuts on
the ends of the all-thread rods that are holding them together, the
shaft starts getting in a bind to the point that I can hardly turn
the control wheel/knob. I've ran across this problem in the past
but it seemed that I was usually able to overcome the binding by
being sure to tighten all 8 of the nuts as equally as possible.
This dosen't seem to work this time though and I've had to just
leave the nuts only finger tight to be able to operate the control
knob. I am using (4) spacers of 2" long pieces of steel tube placed
over the all-thread between each variac and since I had to cut them
out, maybe they aren't precisely the same length. Maybe that's
what's causing the binding? Any ideas?

David Rieben