If the situation is as you describe it is most likely that the plate was
cracted before he got to the piano and the very little stresses (1/1000 of a
tuning stress) caused the plate to seperate.
Plates are designed with a likely 25% safety factor above the usual 40,000
pounds of strain placed upon the plate when tuned at A=440. If a plate
breaks with far less strain then the plate is faulty.
No other conclusion is even remotedly possible.
Newton J. Hunt
Piano Tuner=Technician
RPT for 32 years
nhunt@jagat.com
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