KS 15: Strike Sampling

KS 15: Strike Sampling

Strike is the three-dimensional target and principal index of grand regulating. It is the first line on the piano designer's drawing board. The keybed is a distance from it, the bridges, agraffes and capo bar, the hammer centers, wippen centers, capstans, key pins, and keys. For the regulator, hammerline, letoff, drop, key level, key dip, backchecking, and aftertouch all relate to strike. And, of course, correct placement of strike in our bench setup critically impacts how work will fit in the piano.

What are the three dimensions of strike? Crown of hammer meets unison strings an up-and-down distance from the keybed and keyframe, keys, and topstack must fit and work properly in that space. The forward-and-back distance, adjusted by the cheekblocks, must clear hammers a way between bellyrail, pinblock, and plate to the best place on the strings for tone. And side-to-side distances relate hammer spacing to string spacing. Each of these will be unique to its piano, like an extended finger print of dimensions in space, strung in a line, the strike line, that is likely not straight from any of the three perspectives. The up and down varies with plate crown, overstrung scale design, and relations to belly shape. The forward and back is constrained by hammer bore and hang distances, how worn the hammers are, and where the cheekblocks place them. And side to side, the planes of unison strings may twist from agraffe/capo to bridge, and their layout takes spacing breaks for structures of topstack, bridges, and plate. 

Dynamically, strike is the meeting place of hammer crown and strings the way a clap is a meeting place for left hand and right hand. Their fit or lack of fit affects tone. In the case of hammer and strings, that fit extends back into the action and on into bridge and belly. As we know, a careful mating of hammer and strings improves tone. Lift wire to accomplish this (as opposed to removing hammer felt) to retain the greater simplicity and natural tonal advantages of hammer set integrity.

As a preliminary, modestly lift all wire near agraffe/capo. A light pull easily brings any underlifted strings into the stable zone, better for tuning and better for tone. Strings that are already in the zone will not change. This process reduces curved-steel spring affect and prevents a red herring extra low string from becoming a regulating sample.

Traditionally, a string height tool measures from keybed to strings, providing information for hammer boring or work involving plate removal and restringing. Factories may setup jigs to strike with this information, but piano technicians have largely left strike out of their regulating setup, at least for work on the bench. We sample letoff with the action. Set sample hammers for correct blow distance. And determine a key dip, implemented with a dip block on compressible punchings. Once we validate dip with that block on the bench, we then set up a letoff rack to the samples, set letoff and drop with that, and regulate hammerline to their samples. All of this is prone to error (and worse, accumulated error), partly due to indirect referencing. Letoff, drop, and hammerline happen purposeful distances from strike, not from letoff or each other.

So instead of sampling letoff with the action, sample strike. Remove all front punchings from each sample for extra aftertouch to raise hammer to strings. Feeling where the hammer just kisses the strings and "letting it off" there would be a way to measure strike, but that feeling is complicated by friction, jack-to-knuckle and jack tender-to-letoff button. This method requires too much discretion and interpretation. Adding a weight at the front of the key makes it matter of fact. A WNG Dip Tool is perfect for this: It's heavy enough and self-positions at the front of the key for the same effect in piano or on bench. Let it block hammer against strings and then turn the letoff button until the hammer just lets off. Once bedding is accurately in place on the bench, this method in reverse (blocking hammers with rack and adjusting it to just "let them off") will precisely locate strike. 

Employ a 200 gram weight for flexible strings (generally, note B3) to counter any displacement error from weight-induced hammer pressure (see lead photo).

And do not file hammers before sampling as their wearmarks represent a useful template of string/hammer placement at strike. The wearmarks do present a hazard, however. The straight edges we set up with on the bench can't reach into their "valleys", so move the action slightly right (i.e., place wearmarks between strings) to sample from the "hills" . 

 Next week: Fixing Action Position on the Bench

(Index of all articles in this series)


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