Hi All,  I've heard of only one instance where, after the instrument
was strung, the plate cracked in an area other than near the tuning
pins.  And, I had one instance where the plate cracked in the area of
the tuning pins _while_ the instrument was being strung.

In the second case, I took the plate to a professional welder and
he used some sort of special technique for cast iron.  While I don't
know what he did, it did hold.  In this case, I should also say that
I feel I was very fortunate because the plate cracked in the area of
the sub-bass strings, and I had not yet finished stringing the bass
section when the plate cracked.

Looking back, I remember feeling uncomfortable when I installed the
plate because it wasn't resting flat against the frame in the top left
hand corner, and I had to 'force' it down with the plate bolts and
screws.  After the plate was welded, the plate rested much closer to
the frame in the top left corner.  I figured that when it cracked,
the angle of that portion of the plate changed, and the welder just
'connected' to two areas on either side of the crack, essentially
leaving the angular change alone.

In the first case, the technician never did figure out why the plate
cracked, but his story sounds identical to the one told by Aaron
Carlson (MMDigest 07.06.09) in that the sound of the plate cracking
was likened to an explosion.

I only mention all of the above because it seems highly unlikely that
a plate would crack in an area outside of the tuning pins -- say, one or
more of the braces -- unless there was an unusual stress on the plate
when it was installed.  There are likely a number of 'possibilities'
as to why the plate cracked after the job was finished, but as a tuner
I know that it can take two weeks to two months for a piano to settle
after an aggressive pitch change, and stringing a piano is most
definitely an aggressive pitch change (although I never worry about
a plate cracking).

However, looking at the forces at work on the plate, it gets harder to
see how the plate could crack unless something wasn't quite right when
the plate was installed.  There is so much that we don't know about the
situation about which Aaron speaks that it's fairly impossible to come
to any conclusion as to why it cracked.

Questions like:  Was the downbearing checked?  Was the center plate nut
properly adjusted?  Had the cabinet/frame warped or changed in any
fashion while the plate was out of the instrument?  And if the plate
was never removed, were all of the plate screws tightened before
stringing began?

As sad as it is to hear about such situations, it's sadder yet that
we know so little about the conditions leading up to the damage.  For
without that knowledge, we basically end up shaking our collective
heads and saying, "Oh, that's too bad.  I hope it never happens to
a piano that I'm stringing..."

Musically,
John A Tuttle
Player-Care.com