Ditch the tuning pin bushings - One ? at a time

[Richard Brekne]

David Skolnik wrote:

> The 'Lines of Force'  issue with the tuning pin bushing vs. non-bushing is
> whether the pull of
> the strings on the block in the direction of the plate flange is reversed
> by the pivotal function of the bushings.  Is there agreement on this question?
>
> David Skolnik

Not entirely me thinks. I have yet to hear a completely satisfactory explanation
to all this "how the pivot point affects the pull on the block" affair. To begin
with, it would seem to me that more then anything else, the block will want to
tilt 90 degrees so that the upper face is on a right angle with the plane of the
strings. The plate keeps it from doing so... but the force in that directon is
still there, and it would be there with or without pin bushings. The pin bushings
/ fulcrum thingy just defines the origion of the arc the block would rotate on if
it was allowed to do so. Where a good pin block fit to flange is important then is
to provide as much resitance to this rotation as possible. A good fitting for the
face of the pinblock is important in for the same reason, especially front side of
the tuning pins. If these two areas are well fit to the plate, then together with
the screws holding the back of the pinblock to the plate (those plate screws
directly behind the tuning pins), then the block isnt going to move much at all. I
will grant that all those tuning pins getting support by the bushings in some
sense functions similiar to 230 or so mini plate flanges...but I fail to see how
this provides any critical benifit over an open face system.

I did a little experiement a while back with a block I was removeing. Just prior
to completly taking it out I put on a few strings, and tightenened them up. Only
the back plate bolts were left in and those were loose enough to give a 2-3 mm
play. The front end of the block face immediatlly jamed up against the plate, the
top leading edge of the flange end of the block was slightly tilted down and
jammed into the flange, and the screws got pulled down tight to the plate. I dont
think that block would moved much had I had all the tension on the piano really.

No I agree with the idea that the primaray "benifit" of pin bushings is to support
the pin itself... something you could just as easily accomplish with an open face
block ... as long as the coil to support distance is short enough.
--
Richard Brekne
RPT, N.P.T.F.
Bergen, Norway
mailto:rbrekne@broadpark.no