On Thu, 21 Jun 2018 18:38:38 -0400, Keith Nuttle wrote:

On 6/21/2018 5:51 PM, wrote:
What about attaching the stretcher to a solid sheet of plywood ?
then re-framing to hide everything ? To save ruining the canvas ?
John T.

That may work. IF the plywood were thick enough. A piece of plywood
40X30 would add weight; frame + stretcher + plywood. Thinking: I wonder
how thick the plywood would have to be to be strong enough to pull the
bend out of the stretcher.

To pull *all* of the bend out *at once*, probably pretty thick. What if
you try to pull the bend out gradually, over a period of maybe a month?

A welded steel frame might work even better, and possibly weigh less than
plywood, depending on the thickness of the steel.

Where do you live?