Re: stacking variacs

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Scott Hanson" <huil888-at-surfside-dot-net> 

David -

There's a high probability that your binding is being caused by the spacers
not being of identical length. Unless they were cut off using a lathe with a
fixed stop, they will need to be individually measured to make sure they all
match. Because of the large distance across the variac frame, even a small
variation in spacer length can introduce enough of a angle between the two
variac frames, or distort the frames, to cause binding.

You could eliminate the spacers and just use multiple sets of nuts and flat
washers on the all-thread rod to set the spacing and alignment between the
variacs. This would take a little time to get the alignment set, but would
allow adjustment to a perfect no-bind condition for the drive shaft.

Another approach that will accommodate ALL angular misalignments form ALL
sources is to cut the drive shaft in half and place a flexible shaft
coupling between the variacs. The rubber-biscuit type shaft coupling will
easily accommodate the misalignment that is causing your binding, and is
relatively inexpensive. See McMaster-Carr's website for many different types
of shaft couplings.

Regards,
Scott Hanson
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, April 18, 2004 9:39 AM
Subject: stacking variacs


 > 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
 >
 >
 > ---
 > [This E-mail scanned for viruses by Surfside Internet]
 >
 >

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