Reblitz says the top end of the jack should sit .003 below the rep. lever "so the lever--not the jack--supports the hammer knuckle."

But I think I've read elsewhere that the jack should just touch or kiss the buckskin of the knuckle, thus actually making contact with it.

Is the proper adjustment a disputed issue? Or is Reblitz right and I was just imagining I read a different approach?

The jack should just be ever so slightly below the top of the rep lever. I have never heard anyone suggest differently.

that relates to the spring strenght, the knucke rest on both at rest - too much play is not excellent, too little either.

Greetings,
I think Reblitz was written for the more basic approach, but fine regulation for me depends on the hammer's weight being held by both jack and repetition lever. Since there are different spring strengths and frictions, it is of little use to give a dimension for the rep height. I set them so that I can feel the leather of the knuckle when I move the tender.
Regards,

Ed speaks, I think, to the difference of opinion that I'm referring to.

Some techs seem to me to think in terms of there being--under ideal conditions--the slightest gap between the jack and the knuckle in the resting position (.003 is a small gap). Thus, the hammer at rest is supported SOLELY by the repetition lever.

Other techs (like Ed?) seem to suggest that it is acceptable (even preferable under ideal conditions?) for BOTH the jack AND the repetition lever to be supporting the hammer at rest.

I happen to have adjusted my piano in accordance with the LATTER approach, because I don't like the thought of any superfluous loss of action. Also, it is arguable that a "palpable hit" (to cite the Bard), even if only from a distance of 003.", could result over time in greater wear-and-tear on the buckskin.

What Ed said, and I make sure the jack returns all the way under the knuckle.

How do you check that the gaps between the knuckle and jack and the repetition lever are both .000? As Ed and Bob say, or otherwise?

if you want the hammerline to stay

As long as everything resets instantly and as part of a final round of refinement, it is possible to have a little bit of drop when the tender is pressed. We used to call this "winking the jacks" in both UK and USA.

I make sure the jack slides back under the knuckle at rest. If your working with old knuckles, they will be worn and the surface that the jack touches my protrude further into the "window" then design. You must have hammer raise first off though.

For me, winking the jacks is the only way of getting a stable hammer line and accurate set off (let off).

It can be done with the action in place before final refinement of the hammer line.

Of course I'm talking about an action with all the parts in fine condition. With old parts, do the best you can, knowing all the parameters.

At Steinway they call it "rolling the flys" You are looking for contact, with minimal friction so the jack returns all the way under the knuckle under it's own power. If you have to manually push the jack back under the knuckle, to get it to rest position, the rep lever is too low. Usually in this case excessive wink can be seen, and excessive friction on the jack heel on pressing it will be felt.

Adjusting springs, hammer line, or jack rest position may change this setting - or it may not.....


That's why a fine regulation is more than one pass.

.

.......,,until the adjustments are so small, they make no difference elsewhere.

In fact, Bob's description is consistent with what I've been doing (very time-consuming and back-breaking): 1. Pull the action; 2. Starting at A8, with the hammer at rest--here is the key step--gently nudge the jack lever (that's what I call it) moving the jack out from underneath the knuckle, and then SLOWLY release it. Does it return all the way back to its home position under the knuckle, just barely, with no extra space between the jack and the knuckle?

That's my "refined" test, and I add the following caviats:

1. I say release the jack SLOWLY, because often the jack will easily slip back under the knuckle if you let it "spring" back on its own. That wouldn't be the proper test, as far as I can determine.

2. The jack will return under the knuckle after a hammer strike even where the jack clearly sits ABOVE the repetition lever at rest. So that's not the test. So, again, I return to I what I'll awkwardly call the "move the jack lever out and then SLOWLY LET IT RETURN ON ITS OWN BACK UNDER THE KNUCKLE test" to do a fine adjustment.

Picky and time-consuming, and probably not practical on many instruments, but certainly seems to work as a kind of "fine" adjustment.

Any drawbacks (other than time) to this approach?

The tender, not the rep. lever?

Reblitz suggests to aim for a little drop if the rep. lever is pressed. I.e. the fact that the hammer winks with the rep. lever, indicates than the rep. lever actually bears the (bulk of the) hammer's weight.

Your approach, rxd, would almost suggest to me that the jack is supporting more of the hammer's weight than the rep. lever is? Or are you aiming for an equal distribution of weight between the two, i.e. the hammer drops slightly, if either of the levers is pressed?

You got it. This is an instance where written specs are merely an indication of proper regulation. The specs emerge after the fact as a
best-attempt description of a properly regulated action -- rather than being a pre-defined standard. What is important is the actual function -- rather than whether a particular measurement is rigidly adhered to ( and how can you really measure it, anyway?).

The specs go completely out the window in real-world instances like the two sides of the rep window not being level with each other. Then you may wind up with the jack at exactly level with the lower side.

Greetings,
There cannot be any lost motion between the jack and knuckle, if you want, as Isaac said, maximum consistency in the hammerline. It is also necessary if you want maximum durability from the knuckles, and maximum sensitivity at the key. If there is lost motion, the jack will be moving when it hits the knuckle, and it will flatten them faster.
I like the feel at pianissimo when the jack and balancier( rep) both support the hammer. It reduces the sliding friction as the jack releases, making escapement more transparent. I use tight (7 grams) pinning on the balanciers, and a spring rate that will smoothly lift the hammer as fast as possible without being able to feel it in the key. This allows drop to be set at the same distance as let-off, reducing to a minimum the amount of effort at escapement.
One other thing that might bear mentioning is noise. It is common that there be some noise on older actions when the key is released and the action falls back into rest mode. This is usually due to the knuckle/jack contact. I believe, after seeing the slo-mo films, that when the key is quickly released from check, the spring, operating against the mass of the hammer via the knuckle/shank, pushes the whippen down, causing the key to rise faster than it would through gravity alone. The jack will begin to reset during this "fall" of the whippen and the hammer does not rise before this happens. If the jack is in contact with the knuckle throughout this event, it will not hit the stop as hard as if it is totally unimpeded. There is a reason for the graphite on the distal side of the jack, as it is expected to "ride" the proximal side of the knuckle as the action resets.
Regards,

Yes, the graphite ... against the buckskin... and my secondary issue/question: is the use of a thin (microscopic) application of "micro-fine" teflon powder to the jack/knuckle always a good idea? Could it interfere with the friction or "grabbyness" of the jack against the knuckle?

Teflon treatment is beneficial for movement of mechanics at this friction point. The measurement .003 is the thickness of a paper match package.

The measurement is suspect as previously stated for several reasons the primary one being if the knuckle is soft the buckskin will sink into the rep lever and protrude through the mortise affecting jack travel.

This is where the Teflon soup idea I got from Jerry Groot comes into play. Mixing the Teflon up with some isopropyl will shrink the buckskin slightly and improve knuckle properties at rest and in motion.

The Reblitz .003 is a good starting point but as has been stated, winking will tell you if the jack is resetting.
We cannot omit repetition spring tension or checking height from this adjustment.
You can set the rep lever .003 above the jack but if the spring is too weak, the jack will not seat properly when winked. So the rep lever and jack share in supporting the knuckle.
Also as already stated, the nature of the knuckle will make a difference. The material it is made of, how much wear it has, if it has teflon burnished into it, or, if it is buckskin - the direction of the knap can make a subtle difference.
How about the alignment of the knuckle to the whippen - did either change position?
Then you need to play the note - if it repeats like a machine gun and does not double strike on PPP you got it right.
We are assuming that there is proper friction on all related center pins.

ANother unsusspected reason for Teflon/talcum powder on the KNUCKLE, is to protect the leather from contamination coming from the graphited jack and leather.

it keep the nap clean and not "icing" as it is the case when graphite goes on the leather. Then there is a loss of tactile return under the fingers. That one is yet difficult enough to adjust and keep even, when the knuckles are graphited the touch allows an "all or nothing" touch (supposedly to lighten the touch, in the end it even make squeaks sometime)

I do like to use teflon powder on the knuckle, but only after the rep lever height is set. I prefer to feel the jack and knuckle relationship with a dry, un lubed knuckle.