David, I am not sure I understand your point. That would mean that having the piano on a slanted floor could change it's touch weight enough ? I guess not much. I'd better look for differences in aggravation of friction and mismatch betweenn levers at contact point, that are not seen in geometry (static) while appears as a result when measuring DW UW. But I guess you are not talking of earth gravity there as a composante of mass, but the gravity as a reaction of move (not sure to express it well of course). Best regards. Isaac OLEG > -----Message d'origine----- > De : pianotech-bounces@ptg.org > [mailto:pianotech-bounces@ptg.org]De la > part de David C. Stanwood > Envoyé : samedi 2 novembre 2002 21:14 > À : Pianotech > Objet : 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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