Overs Pianos wrote: > Paul and other commentators, > > >Wouldn't torque from string tension be strictly a matter of the > >distance of the > >string from the axis of the pin (radius) and the amount of tension? > >It's basically > >the same thing as torque from a tuning wrench (sic!) on a smaller > >scale. The same > >force results in more torque when applied to a wrench with a longer > >handle than > >with a shorter one. > > Absolutely, but the friction surface is larger also with the larger > pin, which makes it therefore just as capable of withstand the higher > resultant torque loading. Yes, but higher friction is not a desirable thing. We are accustomed to measuring torque by the amount of force it takes to cause the pin to turn counterclockwise in the block, i.e. in the direction of string tension. However, that is not torque. It is torque minus friction. What about the force necessary to turn it in the opposite direction? It is like measuring keyweight by looking only at the upweight. You need to add friction to upweight or subtract it from downweight to get keyweight. Increased friction lowers the upweight and increases the downweight. Increased friction caused by increased surface contact does, as you say, make an oversize pin just as capable of withstanding the higher torque. However, it also increases the amount of force necessary to turn the pin clockwise in the block. Imagine a pin two inches wide, for example, strung at tension. If the friction holds the pin at 70 in./lb. (the force necessary to move it counterclockwise), imagine the force it would take to turn it clockwise. You would need two hands on the wrench and a team to hold the piano! > >Similarly, the string doesn't have as much leverage on a > >smaller pin > > Do you mean here that it cannot generate the same torque forces due > to the smaller leverage radius? Exactly. > >The part that counts is the radius at the point of string contact. > > Sure, but its the relative holding power of the friction between the > pin and the block, and its torque resistance as compared to the > actual torque developed by the string tension with a given size pin, > which will determine the pin holding ability. Absolutely, but pin holding ability is not the issue. Any pin can be made to hold. The questions are improved tunability and stability. I don't think you or anyone else is claiming that pin diameter is irrelevant. After all, there are reasons that manufacturers use size 1/0 or 2/0 and never larger. These reasons are not mysterious and we have been discussing them on this thread. What I'm saying is that we have more design options when we separate the diameter in the top portion of the pin from the bottom (below the coils). It also means that when we use oversize pins to fit enlarged holes, we don't necessarily have to make them oversize in the part that doesn't fit in the holes. Paul Larudee
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