Adjusting Hammer Drop & Up Stop Screw, Part 2

[Delwin D Fandrich]

Dave Sanderson

Dave,

> Does your post then confirm the legitimacy of inspecting the jack
> in the window relationship as a secondary marker based on the
> primary result of 1.5 to 2 mm of hammer drop as a test?  

If I understand you question correctly…
The fore-and-aft position of the jack in the repetition lever window has
no affect on the function of the screw formerly known as the drop screw,
although—all other things being exactly equal—it will have some affect
on the point of the action cycle at which the jack tail contacts the
jack let-off button. If the position of the jack is fairly far
forward—relative to the front of the piano—the jack tail will contact
the let-off button somewhat late and vice versa. It will not affect the
point of actual jack let-off. However, the relationship of the tip of
the jack to the hammershank knuckle is a whole other topic.

Hammer drop after let-off is the indication we look for confirming that
the end of the repetition lever has been blocked and is no longer
pressing against the hammershank knuckle. As long as the hammer drops
after let-off, the hammer will not be blocked against the string when
the front of the key bottoms out against the front rail key punching.
Assuming, of course, that the amount of hammer drop is adequate.

The 1.5 to 2.0 mm I mentioned is simply a guide to make sure that the
amount of hammer drop is adequate. This dimension should not be chiseled
into concrete. It may well be slightly different in different action
designs. But, it should be close to this distance in all of them.

The total rotation angle of the jack (i.e., how far forward the tip of
the jack travels from its rest position after its tail contacts the
let-off button) is a function of such things as the key and wippen lever
arm ratios, the total key dip distance, the starting position of the
jack, the point of jack let-off, etc. But none of that matters to the
repetition lever stop screw. Its function is independent from the
position, the motion, or the function of the jack. The two only got
linked when someone determined that the two events should happen
simultaneously in the action cycle. If they do, that’s great,
serendipity happens. But if they do not, the deciding criteria must be
hammer-to-string clearance. In other words, the action will work
properly and the pianist will be happy if the repetition lever contacts
the repetition lever stop screw slightly—and in the sequence of normal
piano action event timing, this will be very slightly—early and the
hammer does not bounce against the string. If, however, you have
concentrated on getting the two events to coincide at precisely the same
instant and the hammer bounces against the vibrating string, you’re
going to have a call back.

(Yes, I know that the backcheck is supposed to hold the hammer out of
the way. But we all know this doesn’t always happen. Especially at
pianissimo.)


> Once this marker is properly ascertained, i.e. the proper location in
> the upward and forward movement of the jack for rep lever up stop
> to occur, I'm proposing that it is a very good, quick and accurate
> indicator of where the other up stop screws should be adjusted.

If you’re looking for a quick method of adjusting this screw, at least
in the early stages of action regulation, you can try this:
1)  Be certain there is jack let-off
2)  Be certain the keys are precisely leveled (both naturals and sharps,
please!)
3)  Be certain key dip is at least roughly regulated (again, both
naturals and sharps)
4)  Be certain the repetition lever screws are strong enough to lift the
hammers
5)  Now, while holding down four or five keys with the fingers of one
hand (my left hand, since I’m right handed) adjust the repetition lever
stop screw so that there is a 1.5 mm space between the hammer and the
string target. (I’ve never figured out how to adjust these screws in the
piano. All of my screwdrivers are too long. I guess I need some new
ones.)
This will get you a quick and dirty repetition lever stop screw
adjustment. You’ll have to fine tune it later, of course.

I should add that the hammer drop distance and key aftertouch are
directly related. If the key has lots of aftertouch, it will also need a
lot of hammer drop. If the aftertouch is a bit shallow, you can get by
with a bit less hammer drop.

A suggestion. What little I know about action geometry I learned by
studying action models and thinking. (When I came into this trade all of
this stuff was considered to be trade secrets—assuming, of course, that
anyone actually understood any of it. You never knew, since few would
ever talk about it. It was all a mystery.) Take a grand action model and
play with the relationship between the repetition lever stop screw
setting and key dip. And jack let-off, for that matter.


> (Thinking of it as a similar marker, like the setting of the back checks on an
> upright, how we get the end ones to adjusted properly and then bring
> the others into like spec using a straight edge.)

Since you mentioned vertical action backchecks, I’ll give you something
to think about late at night while you’re trying to sleep:  Why is it
possible (theoretically, at least) to set a consistent hammer backcheck
distance AND have the backchecks in a uniform line in a vertical action
but impossible in an otherwise correctly designed, adjusted and
regulated grand action? Well, it was your own fault, you brought it up.

ddf