Wow! What a discussion. I count myself privileged to peer awestruck into this area of expertise. Many Thanks. Steven Hopp Midland, TX. From: gravagnegang at att.net To: pianotech at ptg.org Date: Tue, 16 Mar 2010 21:51:24 -0700 Subject: Re: [pianotech] Action inertia FW versus SW -----Original Message----- From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of David Love Sent: Tuesday, March 16, 2010 4:59 PM To: pianotech at ptg.org Subject: Re: [pianotech] Action inertia FW versus SW David Love writes: The AR is in the low 5’s measured using my dip/blow tool measuring device. The action regulates with quite deep key dip, around 11 mm, such that I have actually shortened the blow and shallowed the dip by 1 mm to see if what he was responding negatively to wasn’t getting buried down in the keys. While it did help it wasn’t the complete answer. Nick writes: Yes, clues to the problem. 11 mm dip is too much for most of us. My limit is 10.7 mm, and that with a blow distance as close to spec as possible, maybe a couple of mms short at the most, and I consider that a compromise. SWs are I think what would be called Medium High note #1 about 12 grams and note 88 around 5.5 grams. Not that high actually, especially considering the low leverage. Agreed, not that high. Doesn’t fit the “high inertia” profile at all points. BW is around 35 grams--pretty light though his complaint is about sense of too much weight, ironically. Friction from my samples is around 10 or 11 grams in the bass and around 8 or 9 in the treble—a fairly narrow spread. Friction seems low --- a classic indication of fly-away actions. Assuming DW to be 50 (a kind of all around useful standard) and UWs to be 20 (another sort of standard) friction would be 15 grams. When the centers are more or less correct, and hammer weights and strike weights are reasonable, this “standard setup” of 50 – 20 – 15 usually does not elicit a complaint unless there are other issues. FW's appear to be relatively low based on number and placement of leads. This concerns me. Where are these leads, and how many. I like the 3 – 2 – 1 – “none” scenario. When possible, 3 leads in the bass; yielding to 2 somewhere in the mid to late tenor; then to 2 in the mid to late treble; finally to 1 and none in the mid to late high treble. Other things being equal, complaints as to high inertia are indeed rare. BTW, high inertia complaints, as we deduce from our customers (and from our own senses) and seem founded due to the presence of several leads (and these close to the key front) have less to do with the initial stroke as they do to the key and action system reversing itself quickly and repeatedly up and down. Still, presumably the leads imply the existence of heavy hammers along with higher static and dynamic friction to overcome. After a long discussion with the pianist today I think inertia is not really the problem. My present theory is that the problem is a fly-away action. By that I mean that the keys seem to fall away from the fingers too quickly. Leads and low AR will cause this effect. Once the stroke is initiated the action accelerates with not enough control and the pianist gets a feeling of being disconnected from the keys. The pianist feels that he loses control and a sense of weight through the stroke. Also, because this fly-away issue controlling pianissimo playing is difficult and must be done with the utmost caution in arm weight (I can tell this myself as a player). Quite so. Again, extra leads, low AR and low friction, when these all conspire will cause the precise effect being outlined here. Yet there is a sense of resistance that he doesn’t like especially in very rapid passage work. Right: “especially in very rapid passage work”. The dynamically changing and reversing system resistance is one thing, but extra leads in a key rising up to meet the next stroke will have to be overcome with an uncomfortable force. It will feel like resistance. Though it is difficult to know exactly what is going on my current thinking is that because of the fly away tendency there is a natural inclination to be very light with the touch even in rapid passage work instinctively in order to avoid the fly away sensation. Good guess, although I wonder about the ‘resistance’. Does your player agree that s/he has to “pull” his punches in order to control things? What is the repetition spring strength like? If too strong, especially in a fly-away action, the resistance met when the jack and rep lever start to escape is quite rude. In another post, David I. suggested “friction is low...I would consider repinning hammer flanges…. (better) control will be noticeable...” This attempt at a very light touch makes it difficult to initiate the stroke sometimes due in part, perhaps, to the highish SW numbers. Sounds as though you are focusing on the “highish” SW numbers. Perhaps they are borderline, but just over the edge of acceptability for this action. High or “highish” SWs and hammers, coupled with low friction and a too-low AR can be a control-killer. I am leaning toward an explanation that the action ratio is too low and that for this pianist he might be better served with a higher leverage by virtue of a shorter knuckle hanging and lower strike weights keeping the FWs relatively low and the BW the same. Agreed, though personally I would not be too locked into the BW; you may have to fudge. But, the knuckle is one concern; the other big one is the key ratio. Is it higher than 2 to 1 (as measured horizontally)? Of course, with an existing action it’s difficult to test this without spending a lot of money. My current suggestion, then, is to hang two octaves of hammers with 16 mm knuckle shanks (I have some old Steinway hammers on shanks taken from some action rebuilds in the shop) with modified strike weights (lower) that will offset the change in ratio and leave the BW the same. Not too hard to calculate this and do a prior set up on the parts. Then I can just swap two octaves and he can test it out. Always best to experiment, prove the point, when at all possible. But why is the friction low? Are the hammer centers too loose? Key bushings? Whip centers? If so, this would be the very first thing I would try. Tightening these up will increase the touch weight, but at least some sense of control might make an appearance. Still, a change from a 17 mm knuckle to a 16 will (more or less) raise the AR by a half point, (say 5.1 to 5.6) increase DW (FW) by a few points along with friction at the profiles by a point or more. In order to offset or accommodate this, hammer weights across the spectrum would have to be reduced by something like 0.50 to 0.75 grams compared to what they are now. All of this will change the tone. Of course, dip will return to normal parameters. I like your idea, but centers may be too loose for control. Also, it may be that the hammer weights do not require reducing, but that only the AR needs to be raised. It seems as though the pianist needs to feel those keys better beneath the finger tips. The higher AR will do this. But I worry about those leads. The lower SWs will reduce the power slightly … Not necessarily; what is lost in SW (heavier hammer) is sometimes made up for with a faster accelerating hammer head, for a given touch force at the key end. Impact force at the string may not be noticeably affected; still, heavier SWs usually match up better with heavier bellies and higher tensions. It takes a big rock to move a big rock. Generally, I see a trend in a lot of action rebuilding which I think has potential problems and that is forcing the action leverage down very low in order to get the most facile, low inertia performance. I don’t know about this trend, but I imagine you see more of this “out there” than I do. If by low ARs you mean 5 and low 5s, then yes, potential problems. Usually, however, in order to reduce the AR from, say, 5.9 or 6 + all the way down to 5.1 the required key dip (as your point out) will almost certainly be too long. Unless a new keyboard / keyframe and balance point is properly worked out, an existing frame will not allow for such a drastic change. While this undoubtedly appeals to some pianists it can also create problems and not only with regulation (increased key dip), but I’m also wondering if the sense of fly away isn’t also related to an AR which is too low. Unquestionably, but for different reasons than low friction which is the usual culprit. It would make sense in terms of shortening the shank radius and the faster rate of change through the stroke (time to review my calculus). By this I think you mean, “shortening the shank radius (thereby causing a) faster rate of change through the stroke.” A faster rate of change through the stroke implies a higher AR, faster hammer speed and more impact power for a given hammer weight. David Love www.davidlovepianos.com From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of Nick Gravagne Sent: Tuesday, March 16, 2010 1:54 PM To: pianotech at ptg.org Subject: Re: [pianotech] Action inertia FW versus SW This is an intriguing problem, David. Can you offer any more data? For example, how high are the strike weights? The hammer weights (more or less)? How low is the DW and how high is UW (more or less). You say friction is not a problem, any data? Why do you deduce from the pianist that inertia may be the problem? You say, “The only area that can be responsible for the added inertia are the higher strike weights.” Most likely true, but the whole package needs to be considered as (judging from your history on this list) you already know. How low is the action ratio now? Are you able to supply measurements along with method of measuring? Should the overall AR be low for this action, relatively heavy hammers and (possibly) hammer friction centers just on the verge of being too loose will cause the action to feel uncontrollable, and repetition might suffer. The sense being, that once the key is struck, control of the hammer becomes a guessing game, especially for rapid playing. Can we assume that the action spread, elevations and hammer bore are not in question, or at least not likely seriously so? May we have more? Nick Gravagne, RPT Piano Technicians Guild Member Society Manufacturing Engineers Voice Mail 928-476-4143 _________________________________________________________________ Hotmail: Trusted email with Microsoft’s powerful SPAM protection. http://clk.atdmt.com/GBL/go/210850552/direct/01/ -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech.php/attachments/20100318/01e940c0/attachment-0001.htm>
This PTG archive page provided courtesy of Moy Piano Service, LLC