> > How do the 'Lines of Force' differ in an openface block; bushing-less covered > block; covered block with bushings? The force and leverage thing is mostly an issue of how much unsupported pin there is between the bottom of the coil and the highest point of support, be that pinblock top, bushing, or plate contact. This determines the tendency to flagpole, and the psi load on the block. > > Do the 'lines of force' of a bushing-less block change if, over time, the > pins, en masse, begin to contact plate? Would such an occurrence > necessarily be due to poor flange fit, or could either poor top fit or soft > wood be factors? When the highest point of support becomes the plate instead of the pinblock, yes. It changes. For some reason I haven't yet understood, the usual assumption seems to be that the pins touch the plate because of poor flange fit. Look down the back side of these tuning pins, and you can see how the hole in the block has elongated. The lack of pin support near the coil has put a lot of leverage on the pinblock and the wood has simply crushed through the years. This happens with soft bushings too, but slower on average because there is some pin support from the bushing and somewhat lower leverage load on the block as a result. > > How much pressure against what resilience factor (durometer?) would be > required to have an impact on these "lines of force'? At what point does > 'support' begin to alter function? Don't know. The feel of tuning pins with bushings, and those without, all other things being equal, indicate to me that the function is altered immediately upon assembly. > > Would you assume that a new or newly rebuilt instrument without bushings in > which tuning pins already contacting plate is starting out with an acceptable > alteration in its design parameters? Absolutely not. It's starting out with sloppy workmanship. > > What is the intended design purpose of plate bushings? Which are unintended > side effects? > - Dust and beer repellant > - Centering of drilling for tuning pin > - Support against flagpolling / springing > - Alteration of 'lines of force' > - Contribute additional torque to rotation of pin Of these, centering for drilling is the design purpose. The ancillary benefits include flagpoling support, (some) leverage relief to the block, friction buffer between the pin and plate, and giving the technical community something relatively safe and harmless on which to disagree. No additional pin torque resistance is expected, other than the obvious difference in feel between a pin that is riding the plate, and one that is not. That's that friction buffer I mentioned, and I may be the only one out here that is bothered by it. Ignore that one or not, as is indicated. > > How would intended purpose dictate material employed (soft wood, hard wood, > delignit, plate contact) ? The softer the wood, the more necessary to support the pin close to the coil. Harder blocks will tolerate more unsupported pin length because they will take a higher psi load. Plate contact may be all that's keeping the pins in some pianos from rotating forward enough for the strings to pull them right out of the plate. That doesn't make plate contact desirable, but just points out the weakness of the block. > > How do tuning pin bushings contribute or detract from TUNABILITY, as opposed > to tuning STABILITY? To stability, not a bloody whit. I think they improve the feel and control of the process. Opinions vary considerably here. > > To what degree (if any) is the springing / flagpolling tendency a valuable > tuning tool? It is to some degree because you have to spring and torque pins back and forth a little to find out where the segment equilibrium point is across bearing points while tuning. You can't balance string tension against pin spring and back torque if you can't determine aurally where everything is. You do that my moving things and listening - or watching. > > How does the density of the pinblock material used with a bushing-less plate > affect the ability to use springing effectively? Pin fit is a factor. Too tight a fit means you have to torque (and probably spring) the pin quite a ways before it moves in the block. A bushing in these circumstances gives the pin a little more support and takes some of the spring (though not the torque) out of the guessing game. > > What is physically taking place in 'springing'? What is happening to pin, > along how much of its length? to the top of the tuning pin hole or the > bushing? It's bending, but within the plastic deformation limits, so it doesn't stay bent, but springs back straight. It's springing from the hammer socket to the point of firm support in the block. A bushing raises that support point a little, in one direction anyway, making the spring (flagpoling) a bit more manageable. > > What part do characteristics of the tuning pin play in tuning > characteristics? > a) Tolerance to nominal size > b) Type of steel > c) Method of thread formation > d) Finish (blue, nickle, etc) Size makes a difference (yea, yea, I know), in that a 1/0 pin is more flexible and has a smaller pinblock contact area than a 3/0 pin (or whatever). You can feel the difference tuning, though you may not be able to tell why. I don't think you get a choice on the type of steel. Cut threads are the way to go, which is why everyone has gone to them. I don't think finish is a factor unless someone plated over the cut threads and smoothed out those lovely little teeth. I prefer blued pins over plated because I'll never have to wonder if the plating will ever come off, and I like the looks of the blued much better anyway. > > Do small and large ply blocks have different tactile tuning characteristics > if measured at the same static torque? They sure seem to, though I don't have any numbers to support it. Someone posted a set of torque values for a bunch of different blocks pinned with 2/0 pins driven into different hole sizes. Then the values for the same pins three years later. I put them in an Excel spreadsheet for easier comparison and posted it on the Xdrive site. www.xdrive.com user: piano5 password: tech > > Relationship of pin maneuverability to friction ratio of front string bearing > points as a determinant of tunability. What is too little friction? too > much? Too little friction is the Steinway 1098. Too much is the Mason and Hamlin AA, BB, etc. Too high a pin torque makes both nearly impossible to tune. > > Please remember that you will be marked "incorrect' for any questions > unanswered. > David Skolnik I can beat any eraser in the place. Ron N
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