Grand action power train: key (input arm keytop to balance hole, effort arm balance hole to capstan surface) engages whippen (input arm heel to center, effort arm center to jack tip) engages hammer (input arm knuckle to center, effort arm center to hammer crown)

Hammer weights and travel parameters get amplified or de-emphasized depending on the geometry between keytop and hammer crown. Generally, weight reduction at the key equals loss of hammer rise, and each of the three main levers contributes to this as a give and take. Their relative impact varies, of course, so we benefit by having a well-observed hierarchy in mind as we decide what to try. Shifting hammer position a millimeter on the shank, for instance, makes far less difference than shifting knuckle position the same distance, but it may make a critical difference to the tone of the high treble when faced with keyframe positioning inflexibility. The fixed and movable aspects of each action generate their own spectrum of possibilities and somewhere in that mix lies best improvement.

In my experience, the process of trial and error helps solve this puzzle. Even applying sophisticated math requires the trial of implementing its solution. The alternative is to accept the current condition, inheriting its errors and limiting the benefits we can provide. The hazard of the trial may be an error, but the error teaches us. One way or another, we must brave both to excel at this work.

Lately, I have met some extreme variations on the theme. A 110-year-old Weber with failing parts. A 100-year-old Baldwin with replacement parts that were not fitting. And now a 100-plus-year-old Welte with a bit of each. Starting spreads in these actions ranged from 109mm to 115mm, with my choices of replacement parts favoring 112mm. I would argue that since the gradual forces of gravity and wear have altered the proportions of most actions by the time we get to regulate them, and since available parts and materials often don’t match, tweaking geometry has become an important skill to develop.

Let’s take a look at the levers, starting with key on keyframe. We all share the playground memory of a see-saw, fulcrum in the middle, heavier person at one end, lighter person in the air at the other. If the see-saw allows, the heavier person can move toward the fulcrum and/or the lighter person move away from it to achieve a balance. As they ride the now-balanced see-saw, the heavier person, being closer to the fulcrum, will move less distance and at a slower speed than the lighter person. In a piano key, a certain gram weight added at the front (downweight), say 50 grams, can depress the key through dip and lift all that rides on the capstan at the other end. And the loaded capstan, if all but 20 grams (upweight) is removed from the front, may lift it back up. The balance weight, that is the weight at the front of the key that will balance the capstan plus its load, will be halfway between the downweight and the upweight. In this case, 35 grams at the front should balance the key with neither end touching down.

Front of key to fulcrum vs fulcrum to capstan will be about 2:1, suggesting that the front of the key will lift twice the weight half as far. All three levers in our sample note will together lift approximately 10g (hammer) 44mm (blow distance) with 50g (downweight) traveling 10mm (dip). Rounding out for factors too complex to elaborate on here, about five times the hammer’s weight at the key moves its hammer about five times the distance of key travel for a leverage of about 5:1.

Fingers are the engine of this machine and they have a limited range, particularly when resetting and repeating rapidly. But they have plenty of power with added arm weight and a powerful chi stream, so they need an action that converts their modest range of motion from one direction to another and amplifies it sufficiently to accelerate little hammer masses to move strings, bridges, and soundboard from ppp to fff. The whippen and shank together multiply distance by about 10 and the key divides it by 2.

The input arm of the whippen is a little shorter than its effort arm but there have been actions with no whippen, just a direct connection by jack. The whippen’s main role, then, is not as a multiplier or divider but rather as an interruptible connection to improve repetition. Still, it plays a part in the weight and distance balancing. If the knuckle is moved out the shank (lengthening the hammer’s input arm relative to its effort arm) the jack will launch the hammer with more leverage (the hammer will feel lighter) but with less reach (it will need deeper dip and/or a shorter blow distance). If the whippen center is not moved, the jack, regulated to the new knuckle position, will make a shorter effort arm for the whippen (center to jack tip) relative to its input arm (heel to center), making the hammer feel even lighter. Knuckle moving is a double whammy and therefore needs to be employed judiciously. And the benefits to weight (and, by extension, benefits to weighoff compensation) should be carefully considered relative to the cost of blow distance and/or dip.

Changes to jack position not only affect overall whippen leverage, but also affect the jack’s angle of address to the knuckle. Ideally, the surface of the jack should be tangential to the surface of the knuckle at rest (back of jack aligned with back of knuckle core). The transfer of power is weakened, and friction increased, if this alignment has an angle. Also, in this part of the puzzle, aftertouch is reduced as the knuckle moves out the shank and in the other direction, space in the repetition window for the jack to clear after letoff is reduced. The jack must not jam on the stop felt of the window but must just clear the knuckle in aftertouch, so knuckle diameter needs to be considered. Some best-designed heyday actions had 9mm knuckles that reached 10mm from the underside of the shank. A 10mm knuckle has the same reach but a greater diameter to clear and a 9mm knuckle has the same clearance but changes elevations a little. Available replacement parts create this dance of considerations to which the best clarity comes only through sampling.

In modern parts, we can choose whippen heel height and placement. By using heels that are 2mm taller for the sharps, the different geometry between naturals and sharps is mitigated (the half-travel intersection with the line between balance hole and whippen center is about 2mm lower for the sharps). In an action, capstans and hammer and whippen centers line up note-to-note, but balance and front keypins do not. This leverage discrepancy between sharps and naturals will also show up in a staggering of backchecks when fully regulated. The travel of the sharp backcheck being along a smaller circle than the natural backcheck, it travels more toward the player, requiring it to start slightly further back to catch its tail at the same height as the natural.

An important constraint in the optimization game is sharp height. 12.7mm (.5”) should not be exceeded and the sharps must not “bury” in the naturals at full dip. Additionally, natural dip should not exceed 10.5mm (.420”) or blow be much less than 44mm (1.75”). And aftertouch should be comfortable. And there needs to be enough front keypin in the front bushings and enough balance keypin sticking out of the balance bushings. And keys must not show a gap above the keyslip or touch the fallboard. And drop screws must not scrape pinblock or stretcher. And backchecking should be closer to 12.5mm than 16mm (.5” than .625”).

Really, all’s fair in the push and pull, but exceeding these constraints risks transgressing user expectations, whether aesthetic, mechanical, or musical. Also, prudence would recommend imitating original playability characteristics such as same downweights throughout for an action setup that way. When original style parts are not available, we enter the push and pull, like it or not, and should aim for the acceptable zone between these constraints. The customer with specific needs or desires should be brought into the decision-making process, but it can be helpful to make the tradeoffs clear. Everything has a cost, in tradeoff, in labor, in price. Even at any price, some things are not possible. Period. We should withdraw as early as possible if expectations demanded are simply not obtainable.

Mostly, though, the poorly playing grand action offers us opportunities to exceed expectations, be well paid, and enjoy our work.

Next time: Playing with Proportions 

  • Part 1 "Why Weigh Off" 
  • Part 2 "My Strategy" 
  • Part 3 "Method and Style"
  • Part 3a "Regulation Strategy Review" 
  • Part 4 "Pragmatics"
  • Part 5 "Trials and Errors"

    1 comment

    John Keane

    Chris, Your clarity and eloquence in these articles make them a joy to read! Please consider allowing their "powerful chi stream” to be published in the PTG Journal so your knowledge and wisdom can reach a wider and ever-grateful audience! John W. Keane Prior Lake, MN 🙏🎹🦆

    John Keane

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