Bridges continued

[Ron Nossaman]

Hello again Richard,

I still think the bridge would crush as you describe as the strings are pushed up the pins by expansion. The result of either described scenario would be the same type of top damage.

I like the pins heaving up out of the bridge idea. I've de strung more than a few pianos where the pins would probably fall out of the bridge if you turned it over. This could also explain the hammering of the bottom of the skid track I described in my la
st post. I can only see this happening in an environment of very extreme humidity swings, or in an old piano (which this is). I would think it would take a while to get to this point. Good thought.

Ron Nossaman




At 11:40 AM 4/23/97 +0100, you wrote:
>Ron,
>
>Here's some further thoughts about my last post.
>
>The scenario I presented would nicely explain why older pianos have good
>net bearing but little or no front and back bearing. When I measure
>bearing prior to un stringing I use a 3 foot dial indicator gauge. Older
>pianos usually show .005" to .020" of deflection between the feet in
>front and behind the bridge relative to the foot on the center of the
>bridge surface. But when I place the gauge with an outside foot centered
>on the bridge surface the gauge will show little or no deflection. In
>effect I have a bridge with a triangular instead of rectangular cross
>section.
>
>Here's another scenario. Do you suppose bridge pins can heave up out of
>the bridge body due to the same expansion and contraction forces? Just
>as an improperly made building footing can frost heave out of the
>ground, might a bridge pin move up out of the bridge body? If a footing
>is made wider at the top than the bottom it will frost heave no matter
>how deep it is made relative to the frost line due to the expansion and
>contraction of the earth as it freezes and thaws. If were are assuming
>that the pin is looser in the bridge at the top than the bottom would
>this be similar? I'm guessing not because that would also mean that the
>bridge has less grip on the pin at the top and could not pull the pin up
>from the tighter grip at the bottom. But if pins did heave that would
>explain why I can usually tap pins back down into the bridges on older
>pianos.
>
>Richard Anderson
>
> Ron Nossaman