"Joe Landau" wrote in message
. ..
I have a piece of sheet steel that looks to be tinned, about 8x7", that is
part of a 70 year old box I'm refinishing. It has acquired some stresses,
and won't lie flat, though it will spring into several stable states,
like,
boing!. How can I get it to relax, so I can rebuild the box without
stresses?


I have used a slapping technique to straighten sheet metal. I have a piece
of 1" steel -12" X 24" that lays on my benchtop. I take the offending
sheetmetal and in a slapping motion strike down on the plate. Be carefull
not to hit the edge of the plate for obvious reasons. Light hits seem to
work best and if the plate is free of burrs you shouldn't harm your tinned
sheet.
Steve