About the only way to break a good piano plate is to shock it hard
enough to bend it while the strings are still on it. They are otherwise
almost impossible to bust. But defective piano plates are another
I had a plate break one time, right across the widest portion of
the lower treble web. Of all places, it should not have broken there.
The reason it broke was because the plate was defective. Sometimes in
the casting, stress lines are created, due to wide temperature
gradients, or even a movement and jar against the mold while it's
cooling. A powerful clap of thunder at just the right time might also
conceivably cause it.
Curing piano plates outdoors was extra insurance for this at one time.
Let a plate sit outside and rust awhile, and much of that built-in
stress can be distributed a little -- enough that the plate will be
better protected against its own stress. The problem is mainly due to
the complex design of piano plates. If it was a manhole cover, than
that's a different story.
I would think that a customer would have no recourse, unless he could
prove that the technician broke the plate from bad handling or by
accident. If this happens, I suggest a rebuilder understand the
customer's problem, too, and go the extra mile to make it good for him,
but not to provide him with a new piano. That customer, after all, is
taking a chance like this when he decides to have his piano rebuilt.
The chances are almost nil. Most rebuilders have never had it happen
at all, and when a crack is noticed, it's usually in the pin pan, which
doesn't contribute to stringing strength anyway, so it won't be
tensioned when the strings go back on.
Just as a precaution though, any cracks a rebuilder may notice in a
plate should be reported first, before any more work is done.
Regarding my one broken piano plate, I brought the plate to a fine
welder in three pieces: two very large sections and one segment. He
brazed it back together, and promised it would be three times stronger
than originally. It worked wonderfully, and the piano is still being
I asked about cast iron rod. He said simply, "It doesn't work. Here's
how you do it."
He was right.