The sash in the bedroom is really old and needs replacing.
Unfortunately I don't have a spare £800 on me, so it's going to get
refurbished instead. I've done this before so I know how to remove the
beading and get the windows out to works on. The problem is, the frame
has changed shape as a result of a century of settlement and is now a
bit wider at the top than the bottom. This makes the upper pane a poor
fit.

Can anyone think of a way I could build up the frame so it fits a bit
better? I thought about trying to create a very thin wedge and glueing
it in place, but it can't work out how to make one. Or maybe there's
some kind of springy steel product I could get?

Cheers,

John