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I have several specific questions about this topic. But feel free to answer the question in the title of the post in general also. I also know this topic can get incredibly complicated so I hope that tech input(which I am especially interested in) can be phrased so as to be understandable by non techs.

Some specific question (in no special order):

(1) When a tech uses those little weights to measure downweight does this test included friction(or do they tap the front of the piano near the key being tested to overcome friction or?)?

(2) Is it correct to say that two pianos with the same downweight could feel very different because of the mellowness or brightness of the piano(with soft hammers or with a very mellow piano it would require more force to get a certain volume and hence feel like the downweight is more than the weights measure)?

(3)What does the phrase action geometry mean and how does it affect the feel of the piano?

(4) Where does inertia fit in to the picture?

(5) What exactly is being measured when a tech uses the weights(what is the precise definition of downweight)?

#2. Yes that is correct in my experience. In one recent situation, I was sure that two pianos had different downweights until I "played" them so softly and slowly that the hammers didn't hit the strings. They felt the same, and I realized that I was simply having to play the mellower one with more force to achieve the same volume.

Del can probably answer this as well as anyone. Friction, weight and geometry are all cuplrits in how (weighty) your action feels.

It is sometimes difficult to differentiate between friction and actual weight/mass; and they even overlap to create more confusion. A heavy action with little to now friction, can feel much lighter than a light action with lots of friction (for instance).
Bad geometry creates many problems that are typically compensated by extra weight, which leads down a road of no return as one area weighted now requires another area equivalently weighted (Steinway comes to mind with those 5-6 key weights).

An yes, voicing can "make" a piano feel lighter or heavier, though it really isin't.

In response to #2,
yes, psychoaccoustics play a large part in how you perceive a piano to feel.
But looking at the other things you bring up like action geometry, it's very possible for two pianos with the same downweight to feel very different, not taking into account their individual voice.
We're rebuilding an old Steinway A right now, that was previously rebuilt by a very "reputable" rebuilder. The problem is though, that the rebuilder had no knowledge of action geometry.
After replacing the action with all of the wrong parts, he was adding 4, 5, even 6 extra weights to each key in an effort to move all the mass he had added to the other end of the lever.
Even moving the knuckle a millimeter would've greatly improved the action geometry, and would've changed the weighting scheme. This is what we've ended up doing, and are going through and replacing everything now.
I guess what I'm saying is that in the end, all of these things effect how the piano feels. This Steinway had the required downweight, but thanks to all the extra lead, it required so much force to break inertia and move the key that it played like a truck! Hopefully with some slight (although serious) modifications it will play much more evenly, and much lighter, eventhough the downweight may not have changed that much.

I think most techs hit the keyslip to break inertia and get the key moving. With a lot of mass up front, it can take more weight to get the key moving than it takes to continue through it's travel. Hence the "hit".


I'm sure Del can explain this much better than I can, as he is "Del"ving into the subject every day. I'm sure my knowledge of this is limited compared to his, but I hope the information I gave helped somewhat.

PL,

I'm not a tech but I'll take a stab at some your questions. I find this very interesting stuff.

(1) When a tech uses those little weights to measure downweight does this test included friction(or do they tap the front of the piano near the key being tested to overcome friction or?)?

The weights are used to adjust the downweight. Downweight in a piano action has two components. The main component is inertia caused by the mass of the action parts that are at rest. A much smaller component is frictional resistance. The purpose of tapping is to overcome the frictional resistance of action components that interface during the start of the downstoke. (I read a discussion on the PTG forum a while back about lubricants. If the appropriate action components are lubricated prior to the adjustment of downweight, the frictional resistance is much reduced and thus tapping may not be required. However, at least one tech said this makes the job of regulating the downweight more difficult but did not elaborate. I don't know why this would be so.)

(2) Is it correct to say that two pianos with the same downweight could feel very different because of the mellowness or brightness of the piano(with soft hammers or with a very mellow piano it would require more force to get a certain volume and hence feel like the downweight is more than the weights measure)?

I think Sir Lurksalot is right.

(3)What does the phrase action geometry mean and how does it affect the feel of the piano?

Good question. Don't know. To me "action geometry" is a rather nebulous term that's kind of hard to get a grip on.

(4) Where does inertia fit in to the picture?

Inertia is a property of matter by which it remains at rest or in uniform motion in the same straight line unless acted upon by some external force (according to Webster). Hopefully, this was addressed in #1.

(5) What exactly is being measured when a tech uses the weights(what is the precise definition of downweight)?

Also answered in #1.


I'd like to piggyback on your questions a little. Downweight is adjusted with action parts at rest. It's a static measurement and adjustment. There is an additional action regulating procedure that addresses action parts in motion. The so-called Stanwood Precision Touch Design procedure can be used to measure and modify the action's touch or feel. I will defer to Keith and other techs that know this procedure to comment further. Stanwood has a website at http://www.stanwoodpiano.com/first.htm where he discusses his procedure.

JP

I think I'll try to go back to sleep. This head cold is killing me.

I have several specific questions about this topic. . . .

(1) When a tech uses those little weights to measure downweight does this test included friction (or do they tap the front of the piano near the key being tested to overcome friction or?)?

The weights do indicate down weight plus friction. A second measure of upweight should also be taken. The combination gives an indication of friction. If, for example, the down weight is 52 grams and the upweight is 32 grams then the friction is one-half of the difference, or 10 grams (i.e., 52 – 32 = 20, 20 / 2 = 10).

A light tap at the front of the keyframe can be used to overcome breakaway friction but should not be used to encourage downward motion. The key should fall smoothly (and slowly) with a given amount of weight.


(2) Is it correct to say that two pianos with the same downweight could feel very different because of the mellowness or brightness of the piano(with soft hammers or with a very mellow piano it would require more force to get a certain volume and hence feel like the downweight is more than the weights measure)?

Yes. Voicing in general can affect how the pianist perceives the action. If it is necessary to work hard to get the dynamics of tone out of a piano it will seem hard to play. It is not so much “mellowness” or “brightness” as it is the overall dynamic of tone from pianissimo through forte that is the issue here.

Volume in and of itself is a vastly overrated component of piano performance. Most pianos are quite adequate to fill an average room with adequate levels of sound power. Indeed, I now go so far as to say that if there is nothing structurally or physically wrong with a piano and it is perceived to not be loud enough there is something seriously wrong with the room or with the pianists hearing. The piano can only be made so bright and loud. There is a point beyond which the piano’s output ceases to be musical and simply becomes noise.


(3)What does the phrase action geometry mean and how does it affect the feel of the piano?

The piano action is simply a system of levers. Each set of levers has a given ratio. Taken overall each action will have a specific overall lever ratio. In general the phrase “action geometry” is a blanket term used to indicate how the various levers fit together and, by extension, how far the hammer moves in response to a given amount of key movement. If, for example, the hammer moves 45 mm in response to a key movement of 9 mm the action geometry is set up for a overall ratio 5:1. If it is set up such that the hammer moves 45 mm in response to a key movement of 10 mm the action geometry is set up for a 4.5:1 overall ratio.

Obviously, with all other factors being identical, the action with an overall ratio of 5:1 will feel heavier — i.e., it will take more force to accelerate the hammer to an equal velocity — than will an action having an overall ratio of 4.5:1. However, the action with the 5:1 overall ratio will also feel quicker and more responsive. It may also be somewhat more demanding to play, requiring more finesse on the part of the pianist.

Historically, actions have been trending toward numerically lower overall ratios. This means that for a given distance of hammer travel the key travel has been getting longer. In part this has been due to the increasingly heavy hammers that are now found on the modern piano. Without the change in action geometry the touch weights would be frightfully high.


(4) Where does inertia fit in to the picture?

Excellent question. There are two ways to cope with the problem of increasingly massive hammers. One is to set up the action geometry such that the overall ratio is (numerically) lower, increasing the key travel and reducing the amount of physical force needed to depress the key, albeit also increasing the amount of key travel. The other is to add lead weights to the front half of the key. Two actions with given hammer weights, one having an overall ratio of 5:0 and the other with an overall ratio of 4.5:1 can be set up such that each will have the same downweight by simply adding more balance leads to the keys of the action having the 5:1 overall ratio. The tradeoff is that key inertia will be much higher. Obviously this will have an effect on how fast the key can be moved. It will also have an effect on how the action feels, particularly as an attempt is made to play fast passages. On the bench the actions may well display equal amounts of downweight but one will be decidedly more difficult to play quickly and, while it will feel quite nice when played softly (i.e., pianissimo) will also feel much heavier when played hard (i.e., fortissimo).


(5) What exactly is being measured when a tech uses the weights (what is the precise definition of downweight)?

It is simply a measure of how much force is required to overcome the friction of an action and then to lift the hammer slowly to the jack letoff position.

A full discussion of action geometry and, hence, a discussion of downweight (which is only one small part of the question) is going to be a lot longer than this. A book could easily be written on the subject. If you are really interested in pursuing this subject there have been a number of excellent articles written and published in the Piano Technicians Journal. Reprints are available. It is also a question that has been covered at great length on the “pianotech” list. The archives are open to the public

Del

An additional factor is spring tension. Although it is more of a factor in uprights, the repetition spring in grands adds an additional amount of resistance to playing. The more tension, the greater the resistance. As there is a considerable amount of leeway in the proper adjustment of the tension, this can make two otherwise similar actions feel differently. It also affects speed of repetition.

Also, touchweights are measured with the dampers raised, but the weight or spring tension of the dampers also affect the feel. Many pianists play with too much damper pedal because it is easier to play with the pedal depressed. Also, the point at which the damper lever begins to be lifted is one of the most noticable regulation points in a piano. Unfortunately, it is also one of the most difficult to adjust, especially in uprights.

1] The repetition spring in the grand action does not move until jack letoff. Strong or weak it will have no effect on touch weight until that point and by then it is far too late. If the grand repetition spring is set overly tight there is a strong possibility that the hammer will ‘bobble,’ or ‘double-strike,’ against the string. If it is set too weak the jack may not reset and note may not repeat. But this setting will not — can not — affect touch weight or key resistance until letoff.

The conventional upright action does not have a repetition spring. It does have a hammer return spring, but this is not at all the same thing.

2] This is correct. The damper lever function of the grand can affect touch weight. Just as does the damper spring of the upright action. In both cases the effect of damper pickup is noted primarily at pianissimo playing levels. In the grand action the minimum amount of lead in the damper lever and some moderate spring pressure in the bass section should suffice. In the vertical action adding a bit of mass to the damper levers (especially in the bass section) helps a lot. It makes it possible to back off on the spring pressure significantly while actually improving damper function.

As suggested, the pickup point is difficult to adjust and is an important step that is often left out of the regulation process. As is the setting of the damper up-stop (or back-stop in the vertical) rail to limit damper bounce.

Del

A side discussion to this question is the idea of “individually weighed-off” keysets as touted by some manufactures as a feature of fine piano building. In fact it is a substitute for proper friction control, proper geometry control and proper action regulating.

The idea is that at some point in the action assembly each key is weighed-off to some established key downweight. So, if a particular set of action components (primarily the wippen action center and the hammershank action center) happens to be tight or loose the leads are adjusted accordingly to achieve a uniform key downweight. This means that one key can have more or fewer leads than an adjacent key. An action weighed off this way will often exhibit uneven inertia and, hence, uneven touch response at moderate to fortissimo playing levels.

It also means that if the action stack is located incorrectly or one of the action rails is off just a bit leads can be, and are, adjusted to suit. This means that one keyset may end up with significantly more or fewer leads than another. This is probably alright if you play the piano for some considerable length of time and you know, and are comfortable with, what you are getting. It’s difficult, however, to find out some time after the sale that the action in your piano has so many leads it is causing excessive and unnecessary stress on your fingers and wrists.

A better method is engineer the system to function properly with some predetermined (and minimal, in my opinion) amount of counterbalancing leads and then, if anomalies are discovered, whether with individual keys or across the board, they can be corrected at the source.

Del

Not exactly. The repetition spring comes into play when the repetition lever hits the drop screw. The let-off begins when the jack hits the let-off button. (The let-off ends long after the repetition spring moves.) These are independent of one another. If the let-off is 1/16" and the drop is another 1/4", then definitely the drop is before the let-off, for instance. It is desirable not to have the let-off start at the same time as repetition spring comes into play, because you get too much friction all at once. But yes, normally they will be pretty close.

And it is true that the tension needs to be set within certain limits. Mine are narrower than what you prescribe, since if you only set it strong enough so that the note will repeat regularly, you might as well be playing an upright. So my standard is that upon slow release from the backcheck, the hammer should rise to drop, but not so fast that it bounces when it reaches drop. But even within those limits, there is a fair amount of leeway.

This may have been raised with other terminology and I may be off base, but I don't think anyone has mentioned the amount of key dip. This will affect the touch of the piano as a piano with a small keydip will feel "lighter" than one with a larger keydip. This is true irrespective of whether the downweight is the same


Best,

Steve O.

You are, of course, at least partly correct -- I must take issue with a couple of your points. The repetition spring initially comes into to play when the repetition lever contacts the 'drop' (more properly, the repetition stop screw). Exactly where these points occur can vary, I suppose, with the person doing the regulating. Still, there are general standards. For most, including myself, both events should occur simultaneously. That is, the jack tender contacts the letoff button and the repetition lever contacts the stop screw at precisely the same instant. (Hence, my admittedly simplistic comment above — for us the two points are identical.)

The friction you mention is not a factor during normal playing conditions. For two reasons. First, the only friction point of any real consequence is that between the tip of the jack and the knuckle and that remains the same regardless of where the repetition stop screw is set. The friction between the end of the repetition lever and the stop screw is so slight as to be of no practical consequence. To be sure , there is a slight increase in touch weight felt at the end of the key as the repetition lever contacts the stop screw, but even this is hardly felt at anything above the most subtle pianissimo levels. Second, during anything resembling normal playing conditions the velocity of the action components is such that their momentum completely overwhelms their breakaway friction.

A precise and predictable touch at letoff is a factor, however, particularly at pianissimo levels. And most pianists find dealing with one precise ‘bump’ at letoff to be both more predictable and more controllable than trying to cope with two separate events. Most action regulators consider setting the two events together to be particularly important if the action is going to be precisely controllable at pianissimo levels.

In general jack letoff should occur as close to the strings as possible (particularly in a grand) without blocking. Precisely how close this can be is a function of the action design and the compliance of the various felts and leathers involved. Usually it is between 1.0 and 1.5 mm. (For those not metrically literate, 1/16” is approximately 1.5 mm.) This setting has much to do with how softly the piano can be played with consistency and reliability. In other words, it establishes the lower limits of reliable performance. At letoff the hammer goes into free-flight and its velocity must be high enough to carry it from letoff to the strings with enough energy to create meaningful sound. The closer the actual letoff point is to the strings the slower this minimum velocity can be.

The limits I indicated earlier for the setting of the repetition spring are just that, limits. They were not intended to indicate regulating standards. So called ‘hammer drop’ is a phenomenon that occurs only during regulation. Or a keying sequence so slow as to not give the hammer enough velocity to bounce off the strings with enough force to drive it into check. The function of the stop screw, then, is to prevent the repetition lever (and its associated spring) from driving the hammer back up against the strings as the jack resets in preparation for the next cycle. Obviously, if the spring is set on the tight side the stop screw must be set some lower than will be necessary if the spring is set on the light side. Generally, however, a balance can be found at which both the jack letoff and the repetition stop screw can be set properly and the hammer will neither double-strike or fail to repeat. This is usually a point at which, when released from check, the hammer slowly and smoothly rises until the repetition lever contacts the stop screw with no discernable bounce as the repetition lever stops.

If for some reason you don’t want to set the jack letoff point and the repetition lever-to-stop screw point to occur simultaneously there are still guidelines that must be followed. The adjustment of this screw must be such that the hammer is reliably stopped before string contact. In a relatively low friction action (and one that is properly designed) the setting of the repetition spring can be on the light side and the setting of the stop screw can be relatively high. With a stiff action (i.e., higher friction) the repetition spring is generally set a bit stronger and the stop screw might be set a bit lower. Still, it is generally accepted that the stop screw should be set as high as practical. It is generally accepted that this should be no more than double the jack letoff distance. That is, if jack letoff is set to occur with the hammer 1.5 mm from the strings the hammer will drop back a total of 3 mm from the string. Or about 1/8”. It would be a rare action that would either need or benefit from a drop back distance of ¼”. The only one that comes to mind is the Baldwin Pratt-Win action of the Juarez days.

Del

Not necessarily. Key travel is a function of the overall action ratio. The hammer must go from rest to a point approximately 1.0 to 1.5 mm shy of the strings. Rounded off this distance is usually about 45 mm. As mentioned in my earlier post on this subject the distance the key must travel to achieve this hammer travel is determined by the overall action ratio. See my earlier example.

Once the key has cycled through most of its travel the action will reach the jack letoff point. The key must then travel just a bit further to ensure that the tip of the jack will fully clear the knuckle as the hammer goes into check. This distance is called aftertouch and is typically about 1.5 mm. Depending on the action style and design (and its age or condition) you can sometimes get by with a bit less.

Now, assume that an action having a relatively light hammer set. The hammer for A-49 (A = 440 Hz.) might weigh 7.5 grams. Let us further assume this action has an overall ratio of 5.6:1 and is properly balance for a downweight of 52 grams. When properly regulated this action will have an overall key travel of approximately 9.5 mm, approximately 8.0 mm of this travel will actually power the hammer and 1.5 mm will be aftertouch. Now, if that 7.5 gram hammer is replaced with one weighing in at 9.25 grams (yes, my example comes from a real-world situation) the change in key downweight will be approximately 9.8 grams. (9.25 – 7.5 = 1.75 and 1.75 x 5.6 = 9.8) This, added to our original 52 grams will give us a new downweight of 61.2 grams. This is going to be one heavy action even though its key travel is still relatively short.

And, adding leads to balance out the downweight is not going help much. Pianissimo levels will be ok, but the added inertial is going to make forte levels difficult and slow.

If, however, the same 9.25 gram hammer is used on an action having an overall ratio of 4.74 it is going to feel considerably lighter. The hammer will be under control for approximately 9.5 mm out of a total key travel of 11.0 mm and the action is going to feel, while not exactly crisp and precise, certainly lighter and more easily played than the first example. At least until you start trying to hammer out something really fast and find it awkward to make your fingers move that far that fast for any extended period of time.

On balance the most responsive actions will have a relatively light hammer coupled with a relatively moderate key travel. I am told, however, that these actions are a bit more demanding of the player in terms of control and finesse. Hence, perhaps, the modern trend toward increasingly massive hammers coupled with the requisite longer key travel. Some piano makers are now specifying keydip measures of up to 11.0 mm. And they are doing so with quite straight faces and utter sincerity — though I don’t know how they achieve this.

Del

Del,

I have spent time (with my mentor) discussing and testing difference in feel vs. let-off. Granted that all actions can differ in their functionability; having let-off that close (1mm - 1.5mm) can be felt actually blocking in mechanism at pp levels.
This is especially noticeable in the high treble where little mass is available. What I now do is regulate let-off to 2mm or so, and then play the note a few times at app-ppp level to "feel" the action movement and adjust accordingly. If your let-off is too close, when playing slowly and softly you will feel a resitance and obvious loosening as the jack fights the nuckle.
Does this make sense?

I have not found this to be the case. At least not with new Renner or Tokiwa action parts on properly set up stacks. I can see how it might be with worn but still serviceable used components, though. Or are you finding this with new actions?

In our shop a rebuilt action (which always means new hammers, hammershanks and wippens along with new letoff punchings, backchecks, etc.) goes through two rough bench regulations and alignments. It then goes into the piano and under the pounder. (This is an in-house designed and built machine that rolls up to the keyset and plays each key with a medium-hard blow at a rate of two times a second.) The first time around the action is played-in for three hours. Following this the action is removed to the bench and is fine regulated after which it goes back to the pounder for another hour. Jack letoff, keydip and aftertouch are checked and adjusted in the piano as needed and it receives one more fine regulation alternating between the bench and the piano. It is then fitted to the piano where all regulation specs are checked and adjusted as needed. We have not had any blocking under any conditions with jack letoff set between 1.0 and 1.5 mm (depending on the action).

But now you have me curious. As soon as I have some time to spare I’ll play around with my model actions and see if I can get them to duplicate what you are describing. The only idea that comes to mind just now is that there may be something in the jack-to-knuckle alignment that might be causing the hammershank to bounce a bit during letoff. Interesting.

Del

*grin* uh oh, guess who's not going to sleep tonight

The testing of this "feel" instance has been primarly on new Renner actions from Sauter - Schimmel and on up. Again, it is much easier to feel at the pp-ppp levels, on a slow strike in the high treble.
Let me know what you find.

Although I find some of the above posts interesting, I am hoping to get some more input(in layman's terms!) about the questions in my original post. Most of the recent posts are so technical that IMHO only an experienced technician can comprehend them. I realize that threads often get off track, but in my original post I asked for simple explanations. Thank you!

Pianoloverus,

You are in the 1000 post club and have been here a long time. A great deal of it has been spent raising many interesting, post provoking, questions for the forum. I hope you are satisfied with the answers to 1),2), and 5), as they seem to have been taken care of, IMO. I hope I can take a stab at what may be stumping you with the others.

3) Action Geometry - Very difficult to get passed fundamental mechanics if you can not visualize the piano parts described in this thread. I think its safe to say that anybody who has not seen an action model, taken an action out, or seen a regulation done, hasn't been following along too well. You have to learn it to understand it.

4) Inertia isn't a "laymen's" term. Its that property of mass which causes it to resist change in direction, or movement from rest.

I think there may be some knowlege competition going on and that isn't helping. I haven't done what Manitou, or I am sure others, has done with regard to what it is that can be changed to effect the perception of a heavy/light action. From my limited experience, however, I'd say downweight is way overrated as the culprit to a "heavy" action. The spinet my wife grew up playing has 65DW's all over the place and feels very light. There is no mass to those keys, however, and they get out of their own way quite easily (low/no Inertia).

Generally speaking, I doubt that most of the mid-tier to high-end pianos deviate much with regard to final DW's. Its the mass in the keys that is where I'd say exists the variation. The laymen can press one key down and lift the one next to it and sometimes see 3, or 4, lead plugs as an explanation to why things may feel heavy. That's crude, I know, but you are probably not going to get an answer when you ask what the Front Weight is, or be able to take the key out and put it on a scale.

Downweight numbers get batted around all the time because they are easy to quote, fall over a tight range of values (48-52, 46-50, 48-54, etc) and constitute a nice average value that says something. Frontweights, OTOH, don't. They mean so much, buy my saying I have 35 gram FW's is practically meaningless. On another key I've got less than 5gr. You can't average those numbers and say much. Even in professional circles there doesn't seem to be a tidy way of distilling how much inertia there is in an action (how heavy it might feel).

FW is only an indicator within a system, but a good one, as far as I can tell. It usually gets quoted in these curves that techs throw around for all 88 notes, saying its high, or upper-middle, etc. Only in a few instances have I seen techs quote one number from the curve as where the FW begins. The assumption is that they then follow the same familiar curve all they way down in keyweight as they get up to note 88. Its safe to say the vast majority of grands are going to have keys that start out in the bass weighing 25-40 grams, and that's incidentally where my quote comes from. Steinway's "accelerated" actions were notoriously toward the high side. I'd guess Bosendorfer's would come in toward the low end. Both probably have 46-54DW's, give or take.

Pianoloverus, I sincerely feel there is a limit to how much you will understand this stuff while driving for laymen's terms. The path of least resistance may be to shuffle off that laymen's coil and bone up.

Chris

Del (on issues with very close let-off)

I experimented a little on a YC yesterday that had let-off so close it nearly touched strings (Which is apparently said to be ok by some).

On a soft and relatively slow blow it appears the top lever of the rep/lever will push the nuckle enough that hammer can strike string having still not gone into let-off, after hammer has struck string jack blocks against nuckle and this can be felt in your fingers as it must push past strong reistance.

I have three model actions in my office: an old Steinway with Teflon bushings, a current generic Renner and a prototype Langer action that never made it into production (too bad, that, it's a good action design).

The only way I can duplicate the described performance on any of them is to set the jack a bit far back (toward the backcheck) under the knuckle. When I do this there is a brief range through which the hammer can bounce off the target (i.e., the string) and return before the jack fully clears the knuckle. If the speed of the motion is just right the hammershank knuckle can still contact the back corner of the jack before the jack has tripped far enough to provide adequate clearance. The hammershank knuclke then bounces off the back corner of the jack with just enough force to drive the hammer back into contact with the target.

It is difficult to duplicate this effect on the old Steinway action but it can be done. The tip of the jack in this action is about 4.5 mm thick and the back edge is nicely rounded over to an (approximately) 2 mm radius. The Renner action was easy. The tip of the jack on this action is about 5.5 mm thick and the back edge is barely rounded over at all — I’d call it a “broken” edge, no more. There is quite a broad range of fore-and-aft jack adjustment through which I could get the hammer to double-strike nicely off the target. I can not duplicate the phenomena at all with the Langer prototype action no matter where I set the jack. The jack in this action is tapered down to just 4.0 mm thick and the back edge is rounded to an (approximately) 1.5 mm radius.

Now, this is hardly an exhaustive survey or analysis. But, if I were to be hired to research the problem and find a solution I would start by looking at the thickness of the jack and the contour of its back edge.

Lacking the ability to design and install new jacks in a given action the work-around solution would seem to be to set the jack just slightly forward of the normally accepted alignment with the back edge of the wood tenon. Yes, it is a critical setting but, once made, it is quite stable.

The next time I regulate a grand action in the piano I'll pay more attention to this phenomena and see what happens. As I said earlier, I typically set jack letoff at 1.0 to 1.5 mm from the string and I don't have the problem indicated. I'm curious as to why others do.

Del