Hail to the mighty patient antares: If one encounters a soft shank, there is no amount of shank thinning, or voicing that will restore the tone. What your instructor at Bosendorffer was doing was testing for a soft shank. In the Baldwin factory we called them "rubber" shanks. Before installing shanks, we would drop the ends of the shanks on a hard table and listen to the sound. The soft shanks would have a dull sound compared to the good shanks. This little test does not take much time, but will save a bundle of time later if the soft shanks are discarded first. Jim Coleman, Sr.
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