Tuning Pin Size

[Farrell]

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"The larger the size difference between the two portions, the greater =
the risk."

Why would that be? I should think the point at which a pin would shear =
would depend entirely on the metal composition (let's assume this is =
constant), its diameter, and the tightness of the pin/block fit =
(torque). As you make any pin size fit tighter in the block, it will get =
closer to its shear point. As you make any pin smaller in diameter, you =
will move toward a lower shear point. Diameter and torque - I think that =
is all. Why would the diameter contrast between the top and bottom =
portion affect its shear strength? Is there something about the =
machining process?

Or do you mean (by the above quote): 'The smaller the diameter of the =
top portion of the pin, the greater the risk of shearing' (because, of =
course, the smaller diameter pin will have a lower shear strength, and =
will shear at a lower pin torque).

How would the diameter of the bottom portion of the pin affect the shear =
strength? I am assuming that the rebuilder will drill/ream/whatever the =
hole to a proper diameter for the diameter of the pin bottom portion.=20

Terry Farrell =20
  ----- Original Message -----=20
  From: larudee@pacbell.net=20
  To: pianotech@ptg.org=20
  Sent: Saturday, January 26, 2002 5:03 PM
  Subject: Re: Tuning Pin Size


  Good point.  There is a slightly greater danger of this than there =
would be with ordinary pins.  The larger the size difference between the =
two portions, the greater the risk.  However, if the pin is that tight, =
it won't be tunable anyway.  On the other hand, I don't think I would =
advise a 6.75mm. top on a size 5/0 (7.45mm.) base.  I may be =
overcautious, but I wouldn't go over a half millimeter difference in =
diameter (=3D 1/4 mm. radius).  I haven't done the math on the stress =
factors.=20
  Paul=20

  David Love wrote:=20

    Paul: Because of the difference in diameter between the coil portion =
and the block portion, is there any danger of shearing the pin off if =
the pin is too tight in the block? David Love=20
      ----- Original Message -----
      From: larudee@pacbell.net
      To: pianotech@ptg.org
      Sent: January 26, 2002 11:54 AM
      Subject: Re: Tuning Pin Size
       David,=20
      You are right on target.  Comments below.=20

      Paul=20

      David Skolnik wrote:=20

         Paul -=20
        I think you are right.  There has and will be plenty to discuss. =
 I, at least, have already gotten the Feb issue, and also promise to =
read it, but some of my concerns date back to a number of months ago =
when, in response to a particular thread, you first started talking =
about your pin.  One of these concerns is that, as a way of avoiding =
block replacement, they are not viable if, as in many of the pianos I =
see, the original pins are already against the plate, whatever their =
size.
      Yep, there's no way my pins will back the holes off away from the =
plate.  The only good solution there is a new block.=20
        Second, while I understand (I think) the theory regarding torque =
and flex, I suspect that other factors, such as lack of quality control =
of pins, or of the fit between pin and block (whether new or repinned), =
not to mention too much or too little friction between pin and sounding =
length of string, have much effect upon tunability than the diameter =
around which the string coils.
      These are all extremely important, and there is no way that my =
pins are designed to compensate for inadequacies in any of these areas.  =
In fact, one of the cautions I include with the pins is not to =
overtighten them, which is a problem I find with some restrung pianos.  =
My pins do not need to be as tight, because of the reduced torque.  =
Furthermore, the difference between what I call uptorque and downtorque =
(pulling with or against tension) is less with my pins than with other =
oversize pins.  Another point is that the design of my pins frees the =
diameter at the coils to be essentially independent of the diameter in =
the rest of the pin.  Of course there are limitations of strength, but =
otherwise very narrow diameters like 6.75mm. are entirely feasible on a =
base that is as big as you want.  That's the principle that I think =
would be of use to Steinway.  Finally, Klinke, the manufacturer of my =
pins and regular Diamond pins makes just about the most precise ones in =
the business.  I needed that kind of precision for my pins in order to =
get them perfectly coaxial and cylindrical.  Mic them all you want; they =
come out virtually identical.=20
         Remember two things about pin flex...1) It can be a very useful =
tool in fine tuning, and 2) it is affected by tightness in the block.   =
A tight pin with no flex can be as difficult to fine tune as a pin with =
too much flex, whatever its diameter.
      Yes, flex can be useful, and some manufacturers rely on it more =
than others in their design.  I like to minimize it as much as possible =
because it compromises the pin's function as a stable anchor, and I =
prefer to achieve tunability by other means, to the extent possible.=20
         =20
        Now to read your article and find out what you really said..=20
         =20

        David Skolnik=20

        At 11:37 PM 01/25/2002 -0800, you wrote:=20

          Chances are that at this point we get into "but what =
about...," in which case I get to rewrite the whole article on line.  I =
would just as soon wait for the February Journal.  There will probably =
still be plenty to debate, but at least not the stuff I've already =
covered in the article.=20
          Best regards,=20

          Paul


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