bridges/seating

[John W. McKone]

Hi Ron,

My apologies for misinterpreting your question.  I understand now what =
your asking, and I have tried a very un-scientific, but possibly =
enlightening experiment this evening.

I am currently doing some work on my personal piano in my shop. I =
rebuilt this piano (a Bradbury 5'6" reproducer grand) about six years =
ago, and it happened to be my first bridge recapping job. Because of =
this some of the bridge pin placement is, well, pretty embarasingly =
wacky.  A few pins are placed in such a way that there is very little, =
if any side bearing. The rest of the job is fine: good downbearing, nice =
tight well angled bridge pins etc. I took some strings off and checked =
bridge pins and found no *visible* notching in them.

I got to thinking that this would be a great situation to test if side =
bearing played a major role keeping the strings off the bridge.

Here's what I did: With the piano up to pitch, I simply pulled up on the =
speaking lenght side  of a couple of strings until they lifted off the =
bridge, then let go and watched what happened. The strings that had no =
side bearing went right back down to the bridge.  The strings that had =
decent side bearing stayed up! I did several in the sixth octave of the =
piano (this is where the misplaced pins are) and the strings rode up =
above the bridge anywhere from 10 to 15 thousandths according to my =
feeler gauge.

This little test, while not very controlled, would seem to point to side =
bearing, and its attendant friction as one of the major contributing =
factors in keeping those suckers up in the air.

Comments anyone?

John McKone, RPT
St. Louis Park, Minnesota
(612) 280-8375

-----------------------------------------------
>From   : Ron Nossaman <nossaman@southwind.net>
Sent   : 04/11/97
To     : pianotech@byu.edu
Subject: Re: bridges/seating

At 08:58 PM 4/10/97 -0600, you wrote:
>Ron,
>
>If you're asking why the string can creep up against the pressure of =
downbearing and friction, you need look no further than the impact of =
the hammer (on a grand anyway) Especially on a hard use piano.
>
>John  McKone, RPT
>St. Louis Park, Minnesota
>(612) 280-8375
>


Nope, nope, not at all. It's quite obvious that a string can be knocked =
up hill against tension, friction, or anything else you care to name. =
You can here it happening if you work at it. It's quite clear to me how =
a string GETS up a bridge pin. I'm saying that it's not possible for it =
to STAY up off the bridge, AT REST, against tension and side/down =
bearing and pin angle, unless there is something physically wrong with =
the bridge pin. What else would hold it up there magically???? David =
Copperfield plating? There has to be a real reason for an observable =
physical phenomenon. I get enough mysticism and "have faith, trust me" =
metaphysics from Government. Demonstrations can illustrate that it's =
possible (I'm still working on that one), but I don't think anyone can =
realistically champion a fix without a clear understanding of what's =
broke. Let's talk "mechanism". I'm willing to accept the notion that =
this happens only in the context of a rational explanation as to WHY it =
is possible.  Wouldn't you like to know too?


 Ron Nossaman