>>Richard Brekne wrote: >> >> >Folks >> > >> >I keep being bothered by the differing conventions for measuring the >> >ratio of the hammer shank. . . >> > Now the interesting part of all this comes when you compare the >> >different conventions for finding the ratio by measuring lever arm >> >distances. Remember that whatever method is chosen simply must conform >> >reasonably to the ratio established above. >> >> >Now lets take a look at which convention most closely conforms to the >> >already established ratio... >> > >> >> >Its quite obvious which one of these comes out best. Ron Overs replied: >Yes quite obviously if you are interested in determining the weight ratio >of the hammer assembly only..... > > >I have noticed that when calculating the hammer/key ratio by measuring the >lever lengths you will always get a larger figure than that derived by >weight. Only recently did I realise that this is because the weight of the >hammer head is bearing down on the end of an almost horizontal hammer >shank. Therefore the hammer weight is bearing down on the hammer shank >lever at approximately the distance from the hammer center to the center >of the hammer moulding (of course this will vary somewhat throughout the >hammer stroke). When calculating the hammer leverage ratio using the >(hypotenuse) distance from the hammer center pin the hammer strike point, >we will necessarily get a larger figure since the tip of the hammer will >travel further relative to the key front when compared to the end of the >hammer shank. > >I hope that makes sense. When our piano was exhibited at Reno, David >Stanwood made a calculation of the leverage ratio of the action using his >weighing method. He got a figure of 5.5:1. Now I designed the action for >this piano on CAD to have a ratio of 5.8 (at the strike point). What do you mean by a ratio of 5.8? Hammer strike point moving 5.8mm for 1mm movement of the key? > If you take the 5.8 ratio and multiply it by 130/138, you get 5.46. I > believe this may explain the different figures arrived at via the two > different measurement systems. Where do the 130 and 138 figures come from? Are these actual numbers from your action? On your attached sketch you showed 136 for hammer location. >So if you wish to arrive at a measured-lever-lengths figure for the >hammer/key ratio which agrees reasonably closely to the figures derived by >the Stanwood method, you could substitute the length from the hammer >center pin to the strike point with the length from the hammer center pin >to the center of the hammer moulding. > >Ron O. Another problem is that ratios derived from travel measurements that I have seen are based on traveled lengths. Neither the hammer nor the key are traveling in a straight line so using lengths (such as 45mm of upward hammer movement happens in 8mm of downward key movement and therefore the ratio is 5.6) seems erroneous to me. It make more sense to me to talk about traveled angles or arcs (such as 3 degrees of key movement results in 16.5 degrees of hammer and shank movement and therefore the ratio is 5.5). Perhaps measuring in this way would give better correspondence between travel and weight. Phil F Phillip Ford Piano Service & Restoration 1777 Yosemite Ave - 215 San Francisco, CA 94124
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