On Nov 10, 9:38*am, exray wrote:
Tim Shoppa wrote:

Others tell me this is well-known but I still don't have any
understanding
of why metal would shrink or grow with time.

Tim N3QE

Where there's pot metal involved it certainly swells up. *Thats a
scourge in 1920s sets that use pot metal pulleys, brackets and capacitor
frames. *My understanding is that it is due to reaction/corrosion
between the various metals in the 'pot' mix.

Well, my metallurgy knowledge has always been particularly poor.

With the problem variables I have on the shelf, the issue isn't
necessarily
the spacing between adjacent plates but the cumulative swelling
over a dozen or more spacers.

I have discovered that by disassembling the caps and grinding
every 3rd or 4th spacer down by a smidgen that the result seems
just fine.

This only helps on the capacitors that can be disassembled... but the
pot metal spacer problem seems to be worst in the kind that can be
disassembled.

Some later top-quality air variables I have use something that
is either welding or silver brazing to space/hold the elements on a
solid rod. These do not have the spacing problems. They're pieces
of beauty...!

Tim.