Jim, I like your last sentence, it is useless to voice an action out of regulation, and it happen that voicing is hiding some hardness of tone due to regulation.
Control on the hammer/tone is all the pianist want (and hammer energy is fragile, even if plenty of reserve is availeable for some time) THe same happens after hammer shaping, the tone is bright and too bright, but it is generally not necessary to needle much as long as the tone is long and pianissimo controllable.
About what we see of the jcak with the shank up, We see first sometime a different rest position, because the pressure from the knuckle push (more or less depending of geometry and indeed the cushion resiliency) the jack on its cushion (at rest)
Just for that the move of the jack toward front is a little delayed
Then we also see the amount of play (a paper thickness) left between the lever and the jack.
Then, when the action is played normally at the beginning of the stroke, the rolling pressure coming from the knuckle push the jack on the cushion (again, depending of the lining, the pressure will be more or less strong)
But those components must be even from note to note, so it is a good tip for the ones that have not learned the specialized touch necessary to feel the clear bump of the jack. It also allow to detect inconsistencies (most often drop screw left too screwed)
If we leave the jack a little back, the letoff/drop regulation is easier to feel because we feel a "strong" wedging effect when the jack (under the pressure of the knuckle) is stopped by the letoff dowel . even when the jack line perfectly at rest this occur if the hammers are heavy enough.
I suspect that when the jack is left at the middle of the knuckle at rest, when the note is played it goes back enough to be nearer the edge of the core than we suspect (if not we would have more cheating jacks)
The action is faster then, as the jack go toward the keyboard easily, there is also less pressure on the cushion, as if the jack floated, but what makes the tone change is due to the half mm we gain on the 31-32 mm leverage from top of the jack to hammer center (my guess) The shank is accelerated faster, possibly (also) because there is less lost of motion in direction of the jack cushion.
This is really only for some actions, but can help a too "heavy-grounded" tone .
ABout jack lining, the result is different and more precise if the job is done from the back of the action, the paralleled vision is not comfortable nor easy to obtain when looking from the keyboard side (plus I like to have my arm resting on the hammer rail quietly for the drop regulation, tactile feedback is exacerbated, a mirror is necessary to look at the letoff and drop then.
Edited by Olek (03/07/13 10:44 AM)