David Love wrote: "In response to your post (below) ... I'd be interested to know which different methods yielded which results." 1) The 5.9 AR yield was obtained by measuring the levers longitudinally; i.e., no angles at all. For example, key levers are measured parallel, or horizontal, to the key stick. Ditto on whip and hammer shank -- no angles, everything longitudinal (more or less). This is a bit simplistic, but is usually the way the concept of levers is taught in introductory college courses. 2) RE the 5.7 --- measured on angles. The front key lever, per Pfeiffer, is measured UNDER the key to the center of balance hole; the rear key lever is taken from the balance to the top of the capstan (profile). Ditto with the whip and shank --- all angles (see attachment). This method is what is usually taught in action classes, with the at-times difference that the front key lever is taken from the TOP of the front key, and then angles down to the balance hole. NOTE: the short shank input lever at the knuckle is taken as an AVERAGE, which is implied in the attached drawing and penciled in as "1/2 depressed". In the case of the YC action an average shank value of 18.4 mm was used. This is the method I mostly use, tho' I compare with the other two, particularly the longitudinal method above. 3) RE the 4.6 --- measured exactly the same as the 5.7 with the exception that the shank input lever is taken from the shank center pin to the point of contact of the jack-top-to-knuckle at REST --- no half stroke and no averaging of this lever. Some techs measure this way; to me it is unrealistically low. Now, I compared these three ARs with actual hammer rise to key dip and the best "reading" I came up with was about 5.5 to 1 (hard to be precise). This is all a bit crazy as the difference between this "measured" 5.5 and even the highest calculated AR of 5.9 is only 0.40; meaning that at the key end the relative dip parameter relating to 0.40 "AR" is as small as 0.07 mm dip (0.003"). Said another way, push hard enough on the key end to take up the 0.003" dip, and the AR works out to 5.68, which compares favorably to item #2 above. RE the SBR stuff --- thanks. I will consider it. Nick's post: >I recently evaluated a Young Chang action by physically > measuring the lever arms using three different methods, resulting in > three different ARs of 5.9, 5.7 and 4.6. The AR that mostly agrees to > the actual measurement (a bit tricky to do) of dip and subsequent hammer rise is the 5.7 AR. Nick Gravagne, RPT Piano Technicians Guild Member Society Manufacturing Engineers Voice Mail 928-476-4143 -------------- next part -------------- A non-text attachment was scrubbed... Name: Action Ratio.pdf Type: application/pdf Size: 108098 bytes Desc: not available URL: <http://ptg.org/pipermail/pianotech.php/attachments/20100118/b623f26d/attachment-0001.pdf>
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