DerbyDad03 wrote:
On Thursday, June 21, 2018 at 9:00:28 PM UTC-4, Sonny wrote:
On Thursday, June 21, 2018 at 7:07:04 PM UTC-5, wrote:
On Thu, 21 Jun 2018 16:21:17 -0700 (PDT), DerbyDad03
wrote:

On Thursday, June 21, 2018 at 1:19:06 PM UTC-4, wrote:
50 years ago my wife painted a picture on stretched canvas over a
commercial art stretcher. The stretcher is 40X30". The stretcher is
made of "thin" 1X2" The original frame did not add any structural
support to the stretcher.

Over the last 50 years it has developed a bend in the plane of the
diagonal between the corners. ie this meant that one corner was about
3" from the wall when the other three corners were touching the wall
snip
But seriously...

Command strips in each corner. Assuming it doesn't take too much force
to flatten it by hand, I'd bet that Command Strips would hold it flat
against the wall. Those things are pretty strong.

https://www.target.com/p/3m-command-...t/-/A-13713731

I can attest that they can hold up significant weight. I used them to hang a
3'x4' 20lb porcelain chalkbard because the office lease prohibited nailing
into the walls. (Back then I took the lease terms too seriously.)

I glued a wooden strip along the aluminum frame on each side to affix the
command strips. 6 years later it's still hanging, but much like the OP's
issue the chalkboard is bending out of plane. The command strips detached
from the wood along the upper-right corner. That happened after only a
couple of years. It's still hanging there, though. I keep expecting to walk
into the room one morning to see a huge mess.

Point being, the command strips seem less effective at holding something
firm against the wall that wants to pull away.