Function of the rim

[Cy Shuster]

I don't know, and I don't understand the rationale.  My understanding is
that the typical angle is 3 degrees back, away from the hitch pin.

If a tuning pin were a foot long, and only had the bottom 2" in the pinblock
(and the string was attached at the top of the pin, way up in the air), I
can see where a truly vertical pin would perhaps lever the pinblock
backwards towards the keys (at least, the bottom layers of the pinblock).

My best guess (having never driven a pin, just measuring my piano) is that a
pin is about 2" long, and is in the block about an inch.  The strings on
mine are about 1/4" above the (bushed) plate.  So, let's see, the part of
the pin above the string doesn't really count, so we have a lever 1/4" long
(the part in the air that can move sideways...easily, anyway...), with the
fulcrum being the top of the pinblock (way oversimplified: I'm sticking my
neck out here with this expert crowd, so be gentle!).

Angling the pin back 3 degrees means there's now some forward (towards the
hitchpin) component to the force vector, as applied to the top of the block.
If it were 90 degrees back, it would be 100% horizontal resistance, so this
gives it 3/90ths more horizontal resistance.

Assuming the pin doesn't flex that much, I guess there's not as much
difference in resistance to the string tension, as there is a difference in
how the part of the pin in the block puts pressure on the block.  Does this
analysis make sense?

And by "plate flange angle", I assume they mean the "v" in the plate that
opens towards the hitch pins, that the block mates to?

--Cy Shuster--
Rochester, MN

----- Original Message ----- 
From: "Avery Todd" <avery@ev1.net>
To: "Pianotech" <pianotech@ptg.org>
Sent: Monday, September 01, 2003 3:58 PM
Subject: Re: Function of the rim


> Cy,
>
> And your answer is????????? Mine would be 'B'. Of course, that's probably
> wrong. :-)
>
> Avery
>
> At 01:43 PM 09/01/03 -0500, you wrote:
> >Charles raises a good point: it specifically mentions the outer, not
inner,
> >rim.  Do they function differently?  The outer rim contacts the lid while
> >the inner rim doesn't...  And, David, certainly it has an acoustic
function,
> >but certainly not by resonating...
> >
> >Here's another head-scratcher.  I didn't find any other clinkers.
> >
> >75) The tuning pin hole is drilled at a slight angle to the pinblock
> >primarily in order to
> >
> >                 A. create an orderly row of pins
> >
> >                 B. resist the pull of the string under tension
> >
> >                 C. create a better lock of the pinblock to plate flange
> >angle
> >
> >                 D. satisfy tradition
> >
> >
> >
> >In their answer key, the right answer
>
>is.........................................................................
.
> >............................................................. C
> >
> >
> >
> >--Cy Shuster--
> >
> >Rochester, MN
> >
> >
> >----- Original Message -----
> >From: "David M. Porritt" <dm.porritt@verizon.net>
> >To: <pianotech@ptg.org>
> >Sent: Monday, September 01, 2003 12:16 PM
> >Subject: Re: Function of the rim
> >
> >
> > > Cy:
> > >
> > > If the written test is supposed to be given to see if someone is
> > > qualified to take the other tests, that's not an appropriate question
> > > in my mind.  There are too many "correct" answers there.  I
> > > personally think it has a cosmetic function, it does add mass to the
> > > rim to provide an acoustic function, it obviously does give a place
> > > for the top to rest.  Provide a support for soundboard crown seems to
> > > be the most incorrect of all the answers to me.
> > >
> > > Are there any other obvious clinkers in that test?
> > >
> >
> >
> >_______________________________________________
> >pianotech list info: https://www.moypiano.com/resources/#archives
>
>
> _______________________________________________
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>