Hi all,  I have been next to one when it broke.  It was a German
upright and it broke shortly after it was tuned.  It made a nasty
noise.  It broke in the curved part of the frame where the mid-treble
strings are located.  The curve at the bottom broke in two and some
of the pins that hold the strings flew out as the crack went through
these.  We had done nothing to this piano except to tune it.

We took the frame out and it was lucky because the area around the
tuning pins was open, with the frame going around it.  We left the
strings on the tuning pins, unhooked them at the bottom and taped
them into bundles to allow them to pass through the frame.

I had the frame welded and the guy heated it with an oxy-acetylene
torch and then used an arc welder with cast iron rod to weld it back
together.  I didn't trust it and neither did he, but that was all we
had available. I had two 8 mm steel plates made in the same shape as
that curve and these were drilled and bolted onto the existing frame
from the front and behind.  It worked and that piano was fine and we
never had a problem with it again.

Some of this is just plain poor casting and the German pianos seemed
more prone to it because they had thinner frames that the American
pianos.  I have seen dozens of German pianos with cracks in the frame,
mostly around the sides and in the treble section.  None of them ever
broke and they stayed in tune as well as any other piano.

Kind regards,
Bernt Damm
Sydney