Grand Regulation In Detail - Part 6

Section III. Alignments

29) Align jack to knuckle core

In order for the power to be transmitted from the whippen to the hammershank efficiently, the jack must be properly aligned under the knuckle. 

Looking at the action sideways, the rear of the jack (the surface towards the hammer) should line up perfectly with the rear of the knuckle core. Normally, this alignment is easy to see. The knuckle should be glued on perpendicular to the shank, and if the hammer is new and was bored correctly, the shank should be perpendicular to the jack. Sighting along the rear of the jack, it should be easy to tell when the jack is in line with the knuckle core.

However, if the shank is not perpendicular to the jack this alignment is hard to see. Two things can cause this:

A. The hammer has worn resulting in the capstan being turned up to keep the blow distance close enough. The shank then becomes more than 90 degrees from the rear of the jack. In such cases, imagine a line drawn from the rear of the knuckle core down to the point on the knuckle leather where the jack would touch it. Then line up the rear of the jack to this point.

B. The other reason, which is fairly common, is that the hammer hole was not placed correctly in the molding. This results in the top of the hammer, either, being too high, or too low in relation to a line drawn down the middle of the hammershank.

Boring the hammer wrong of course results in the shank not being perpendicular to the jack as in cause A. If this angle of the shank to the jack becomes too great, then either the hammer has worn excessively so that it should be replaced, or if the hammers are new, then the hole in the molding should be plugged and rebored.

Why was the hammer bored incorrectly? Have you ever noticed when regulating the hammer-blow distance, that when the tops of the hammers are adjusted so they all are, say, 1 3/4” from the strings at rest, that the hammers in each section vary as to their heights measured from the keybed to the top of the hammers?

We should expect the bass hammers to be higher since the bass strings are higher so they can cross over the tenor strings. But notice that if the agraffes are not the same height as the capo d’astro, the hammers will also vary in their heights between these sections.

If the original or duplicate hammers were not bored taking into account these different string heights, then the hammershanks will not be perpendicular to the jacks with the hammers at rest.

We will discuss this problem further in a later post on hammers, but let me add here that some pianos have a different string height for each section!

An easy way to align all of the jacks is to align the end hammers in each section, and then by using a straightedge or a thread, align the jacks in the respective sections to the end samples.

Note that some manufacturers mark a line on top of the balanciers. This line serves as a guide only when  ...

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