string seating - was bridge caps

[Richard Brekne]

Ron Nossaman wrote:

> >I have no doubt that the bridge is moving, what I questioned was whether
> >this was
> >the reason (or how much of the reason) for the string indentations. As I
> >said, with
> >positive down bearing it would seem to me the same indentations would come
> >about
> >anyways. Grin...
>
> The difference between static downbearing and bridge swelling bridge
> grooving should be pretty dramatic. Downbearing at 1° and 160lb is a little
> over 9 lbs. The resistance to the string being pushed up the bridge pins
> has to (not should be, but HAS to) be considerably more. Where are all
> those engineers that abandoned all that expensive training to take up piano
> thumping? Someone please come up with the math for this one. I'd really
> like to know how to compute this.

Hmm well its an interesting problem anyways.. I would like to know the math on
this as well, just how much of a factor bridgepins that "stay put" (vertically) in
the face of a swelling bridge contribute to the indentation at the edges of the
bridge visa vi other contributing factors.

But regardless of how the indentation is created... the rest of what you have been
saying makes perfect sense. If the indentation is below the string bearing angle
(can I call it that ? grin) then seating strings down into that indentation
accomplishes really nothing...

>
> >I suppose you wouldnt mind explaining the significance of
> >1470 psi
> >here...
>
> Fiber stress proportional compression limit for hard maple... what else?
>

Kinda figured it was something like that... but didnt want to take anything for
granted...:)

> > If you get a chance you might describe your experiment a bit for us.
>
> I had the chance, and have already posted it for Paul when we were talking
> about pin height above the bridge surface. Weren't you paying attention?

Missed it... sorry... would like to read it so I will try and find it in the
archives.

> But I don't see how tapping between the pin rows can do anything at all
> unless the strings are driven into the bridge until the groove underneath
> is nearly flat from notch to notch. Again, that's my point.

Well there's the kicker aint it.. I dont understand exactly why this need comes
about either... but there it is. For whatever reasons, sometimes the string looses
solid contact with the bridge yet the scenario you describe is not present. Now if
you can prove that this is in error....Actually I suppose we could all help to put
some facts on the table... wouldnt be so difficult to make some rough downbearing
and other relevant measurements to establish whether or not strings can be seated
at all without the conditions Ron describes being present....or what ?

>
>
> >I wasnt really challanging it... just didnt quite get your meaning. Still
> >unclear
> >as to how this in itself can cause a false beat, if thats what you were
> saying.
>
> Yea, challenging wasn't exactly what I meant.. questioning. The cause of
> the beat would be that the string is touching the top of the bridge to
> within "X" distance of the bridge pin, but not *at* the pin. On the
> vertical axis of string excursion, the termination is past the bridge pin
> and farther in on the cap. On the horizontal axis, the termination is the
> bridge pin, but if the pin isn't tight in the top of the bridge, it will
> flagpole. The poor effective termination from the flagpoling causes the
> beat as the termination moves left and right with pin flex. The termination
> at the bridge top not being at the pin makes this horizontal movement
> possible.

Grin... well why didnt you say so in the first place... lol. yes I see this. It
perhaps would also cause a false beat at the fundemental... (two effective string
lengths) ?

>
>
> >What would happen I wonder if you took oversized bridgepins, and notched them
> >purposely to hold the string in place vertically....grin..
>
> That might actually work very well.

>
> Ron N

--
Richard Brekne
RPT, N.P.T.F.
Bergen, Norway
mailto:rbrekne@broadpark.no