The Truth About ABS

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Some consequences of using wood in a piano action are
easier to see.

When critical wooden components (such as the jack) break under repeated high stress, keys simply cease to function. In such cases, the failure of one essential part causes failure of the entire assembly... and the consequence is clearly seen.

But one of the most serious problems associated with the use of wood in a piano action is more difficult to see.

Broken Wooden Jack

The place where the hammer strikes the string is perhaps the most critical point of a piano action. Precise alignment of the hammer is essential, since even the slightest change in hammer position can drastically affect tone and touch.

What maintains proper hammer alignment? A crucial part called the hammer flange. When the hammer flange remains secure and perfectly positioned, the corresponding hammer stays properly aligned.

Hammer and String

Hammer and Flange
But on a typical humid day, any wooden hammer flange will begin to swell. As this occurs, the wood under the action screw expands upward against the screw head and eventually becomes damaged. Later, when humidity subsides, the wooden flange shrinks... leaving a "gap" between the flange and the screw. This gap allows the flange to drift out of position. To make things worse, the gap widens as the flange movement causes the screw to loosen. All of this means severe trouble for the hammer alignment.
Swelling Wood Flange Shrinking

Once alignment is compromised, serious problems occur. Hammers hit strings partially (causing "buzzing sounds") or miss strings entirely, resulting in severe loss of tone. Drifting hammers can rub together, damaging the piano's touch or causing notes to stick. Once repaired, these problems can easily reoccur whenever humid conditions return or when the piano is moved into another environment.

Recognizing that wood could never be truly consistent through changes in climate, Kawai craftsmen came to an important conclusion... it was time for a change.

Misaligned Hammer

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