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 >
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