Grand Regulation In Detail - Setting The Hammer Blow - part 12

We left off talking about the two factors that create the striking point for a hammer. Assuming that the hammer glue joint is 90 degrees on the shank, which it must be, these two factors are: 1) The distance from the hammershank centre pin to the centre of the hammer molding, and 2) The position of the hole in the hammer molding, more commonly called the hammer bore distance. In measuring factor number one, the measurement is always taken from the centre of the centre pin, to eliminate any error because of larger centre pins.

Looking at the diagram, this distance for factor number one is labeled (L). In this particular instance, (L) = 5 1/8“, which is a common measurement. (L) determines the type of arc that the hammer will take on its upward movement towards the string. The distance that the hammer travels in this arc is labeled (S). (S) is correctly termed the hammer travel distance. Note that this is different from (6) the hammer blow distance. These two words should not be used interchangeably.

As the hammer is moved in or out on the shank, this distance (S) changes. Minute alterations of (L) by the technician as he glues on a set of new hammers is acceptable in order to achieve the correct striking point. However, keep in mind that the piano was designed with a specific distance for (S). The work that the knuckle does in raising the hammer is in a ratio which is dependent upon (L) and the placement of the knuckle. The closer that these two placements are to what was designed, the better the action will perform.

Of greater importance than factor no1 is factor no2, the hammer bore distance. I regularly find good make grand pianos where the bore distance is wrong from the factory! When manufacturer installs the hammers, he should measure the distance (A) on the diagram. This is the distance between the bottom of the string and the centre of the centre pin on the hammershank. Unfortunately, many pianos are manufactured without regard to this measurement. (A) does fluctuate a little from what the piano was designed to be, mostly because of differences in the thicknesses of the plate castings. Sometimes the string height varies because of improperly installed agraffes, or in the case of a rebuilt piano, the string heights will vary because the plate was lowered in order to achieve proper downbearings.

When rebuilding, always wait until the new strings are installed before sending off for new hammers. Never buy stock hammers. Insist that the hammers be bored to match the piano. Either send to the hammer duplicator the measurements for (A) for each section of the action, or else bore your own. Anyone who has regulated many actions will have noticed that the string heights vary not only between similar pianos of the same make and model, but will also vary between the different sections of one instrument. Ever wonder why the hammer rest rail never fits the bass hammershanks like it does the tenor? One cause can be improper hammer boring. Why? Most grands are made with the hammers bored at a stock distance, to supposedly fit all of the pianos made of that model(s). No interest is paid to what (A) is, or whether (A) is the same for each given section of the action.

Why is this so important? 

 

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