David S wrote: referring to measurements of action ratio Stéphane shows an analysis with mixed types, some touchweight and some geometry. One or the other please! I'm not sure why it should matter if measurements are being taken accurately. To my understanding of the working of levers is that the relationship between distance and force leverages is not idiosyncratic but a fundamental principal of mechanics. As RB has stated, the fact that at 5.5 ratio, 10 mm dip gives 55 mm of hammer travel and that should be plenty when we only need 44.5 doesn't adequately take into account what happens after let-off button contact by the jack tender. Though there may be some efficiency of distance lost by the sliding motion between friction points (namely capstan-wippen heel) that loss of efficiency would not seem to improve the ability of the action to regulate with full specs, rather, it would seem to diminish it. I am still strongly inclined toward setting up actions with great consideration given to determining an action ratio that will give proper regulation specs. If there is a desire to use hammers whose weights fall outside of the boundaries that allow for a good match of weight to leverage, then other solutions, or compromises will have to be considered. For 99% of the actions I do, that seems unnecessary. For that other 1%, assist springs seem to be the most reasonable solution. David Love ----- Original Message ----- From: "Richard Brekne" <Richard.Brekne@grieg.uib.no> To: "Pianotech" <pianotech@ptg.org> Sent: November 03, 2002 9:40 AM Subject: Re: action ratios You see the thing is, that either the ratio is the cause, or its not. Theres not really any inbetween here. Thats why its kind of important to confirm or deny whether a certain level of ratio neccessarilly results in inadequate jack clearance for given parameters. So if we take 10mm dip, 44.5 mm blow, 1.5 mm letoff as a standard, and say alllow for +/- 0.15 mm dip for wiggling room then it should be relatively easy to establish just what level of ratio (on the low end) actually does start causing problems. If you can regulate within these parameters at 5.0 as David Stanwood reports, well then you can. And if you run into a piano that has some difficulty at this low level then perhaps we should be looking at other action relationships to find the source of the problem, instead of just blaming it on the ratio itself. But to be sure... at some point the ratio will be low enough to make the action impossible to regulate for the standard parameters given above. And of course we will have the opposite situation at the other end of the action ratio spectrum. RicB David Love wrote: > Just to clarify my position on this a bit, I haven't yet encountered an > action where low ratios below 5.5 didn't create regulation compromises that > I found undesirable, and there it was pushing it. I hesitate to state a > general law because there may be other factors of which I am not aware. I > was surprised to hear David S. comment that he achieved 10 mm dip 44.5 blow > with an action that measured 5.0. That has given me some pause but doesn't > change my own experience. I have found it difficult to get a consistent > measurement depending on the method used and it is difficult to set up the > action with only a .01 margin of error, so I reserve judgment. For now, > however, I shoot for 5.75, if it drifts down a little bit in my setting the > cap line, for example, I don't lose any sleep over it. > > David Love > -- Richard Brekne RPT, N.P.T.F. UiB, Bergen, Norway mailto:rbrekne@broadpark.no http://home.broadpark.no/~rbrekne/ricmain.html _______________________________________________ pianotech list info: https://www.moypiano.com/resources/#archives
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