Larudee's mystery - Was: Ditch the bushings

[Joseph Garrett]

There are two questions I would like to ask. 1. When and how did the piano
industry/Steel industry decide on the current diameters of tuning pins.
2.Why are "Olde" pianos, such as English "Bird-cage"s and Square Grands,
that have 1/0 or smaller tuning pins, so difficult to tune, that most techs.
refuse them?
Your statement that, "Any pin can be made to hold" makes me curious. I
suppose, if you fill the hole with epoxy or cement or whatever, it would
hold, but would it be utile?
regards,
Joe Garrett
----- Original Message -----
From: <larudee@pacbell.net>
To: <pianotech@ptg.org>
Sent: Thursday, May 17, 2001 8:12 AM
Subject: Re: Larudee's mystery - Was: Ditch the bushings


> 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