That makes sense. Thank you. Stéphane. ----- Original Message ----- From: "David C. Stanwood" <Stanwood@tiac.net> To: "Pianotech" <pianotech@ptg.org> Sent: Saturday, November 02, 2002 9:13 PM Subject: Re: action ratios | He Stéphane, | | The reason I can imagine is that the force vectors are not perfectly | aligned with the force of gravity. I'm probably not saying this right. | Think of it this way,...when the hammer starts out, it's not parallel to | gravity for instance..... If all the levers centered around a horizontal | line, maybe it would be closer. The extreme is the Upright, just doesn't | work there because the parts are aligned vertically. | | David | | | | At 08:32 PM 11/2/02 +0100, you wrote: | >Hi David. | > | >I plan to do a more in depth study of your metrology. Maybe I sould not | dare to jump into this discussion before that. But isn't there a certain | analogy between ratios given by geometry, and ratios given by weight | comparing ? If difference exists, could you explain that ? | > | >Best regards, | > | >Stéphane Collin. | > | > | > | >----- Original Message ----- | >From: "David C. Stanwood" <Stanwood@tiac.net> | >To: <pianotech@ptg.org> | >Sent: Saturday, November 02, 2002 3:51 PM | >Subject: Re: action ratios | > | > | >| Dear Stéphane & Friends, | >| | >| I see some confusion in the discussion about what ratio is. This is my | >| view: When we talk about touchweight we refer to weight ratios and in this | >| regards we refer to strike weight ratio which is the amount of weight, at | >| the front of the key, that it takes to balance a gram of weight at the | >| hammer. When we talk about geometry we refer to distance ratios which is | >| the distance the hammer moves for a given unit of distance at the front of | >| the key. Stéphane shows an analysis with mixed types, some touchweight | >| and some geometry. One or the other please! | >| | >| The discussion that we have been having is about strike weight ratios | >| unless said otherwise. The calculation | >| of strike weight ratio is found by determining the Top Action Balance | >| Weight which is front weight plus balance weight. It's the total upward | >| force at the front of the key from the hammer/shank & wipppen. From this | >| we subtract the Wippen Balance Weight which is the Wippen Radius Weight | >| times the Key Weight Ratio. The result is the Strike Balance Weight or the | >| upward force at the front of the key resulting from the weight of just the | >| hammer/shank. Divide this by the strikewt and we have the strike weight | >| ratio. | >| | >| I would like to offer a more direct way of determining strike weight | >| ratio... a "Short Cut". It also might help some to understand conceptually | >| what it is.... | >| | >| Short cut method for determining Strike Weight Ratio: | >| | >| 1. Make sure the key bushings are free and lubricated with try Teflon | powder | >| (generally recommended whether or not your taking this measure) | >| | >| 2. Make a platform jig that may be mounted on the back of the key for | >| holding temporary weights: | >| | >| http://www.stanwoodpiano.com/ratioshortpic.jpg | >| | >| 3. Flip up the hammer and put key leads on the platform at the back of the | >| key: | >| | >| http://www.stanwoodpiano.com/ratioshort.jpg | >| | >| 4. Put key lead weights on the platform jig and arrange them so the | >| key/wippen are zero balanced. The key is zero balanced when you throw the | >| key down so it bounces back to center and when you throw the key up it | >| bounces down to center in a like motion. If the motions are different then | >| move the weights until the motion is the same in either direction. You can | >| also use a gram gauge and move the key up and down at the front. When the | >| scale readings are the same in either direction the key is zero balanced. | >| If the key has no keyleads in it then you can probably use a small keylead | >| at the front end of the key without using the platform. | >| | >| 5. Flip the hammer/shank down and leave the temporary weights on the back | >| of the key. The weight at the front of the key is solely from the hammer | >| and shank as the key and wippen have been zeroed out of the equation. | >| | >| 6. Measure Up/Down and calculate the Strike Balance Weight (D+U)/2. | >| | >| 7. Divide the Strike Balance Weight by the Strike Weight to find the Strike | >| Weight Ratio. | >| | >| Measure at least six samples to calculate an average level of SBW. I | >| recommend notes 16,17,40,41,64,65 to get a sampling across the most played | >| parts of the keyboard. | >| | >| Hope this helps... | >| | >| David C. Stanwood | >| | >| | >| | >| >> 5 mm dip gives an average 25.5 mm hammer rise (linear, not | >| >> angular, but anyway I couldn't achieve a precision | >| >> measuring so this matters). I assume this is a 5.1 ratio action. | >| >> | >| >> Sorry for WW and FW, but this piano is in very last stage | >| >> of rebuilding, and waiting for customers, so I'm not about | >| >> to pull the stack out of it now. | >| >> | >| >> But I measured KR through length between balance point and | >| >> front key, just above the front pin (243 mm) and length | >| >> between balance point and whippen center for the rocker leg | >| >> (no capstan on older Bechstein) (140 mm). This should give | >| >> us a KR of 140/243 = 0.576 | >| >> | >| >> Here are the other measurements | >| >> | >| >> note DW UW SW | >| >> C-3 60 40 8.4 | >| >> C-2 60 39 8.4 | >| >> C-1 63 47 8.9 | >| >> C0 62 39 8.3 | >| >> C1 57 36 7.3 | >| >> C2 56 35 6.5 | >| >> C3 56 32 5.8 | >| >> | >| >> What do you think ? | >| >> | >| >> Greetings, and much respect. | >| >> | >| >> Stéphane Collin. | >| | >| | >| | >| | >| _______________________________________________ | >| pianotech list info: https://www.moypiano.com/resources/#archives | >| | > | >_______________________________________________ | >pianotech list info: https://www.moypiano.com/resources/#archives | > | _______________________________________________ | pianotech list info: https://www.moypiano.com/resources/#archives |
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