Bridge Pins & Nega Bearing

[william ballard]

Hi Dale,

On Apr 23, 2006, at 10:43 PM, Erwinspiano at aol.com wrote:
>> Then some tremendous force must be at work, because strings which
>> have crept upwards against slanted pins and side-bearing are a
>> regular part of our day.
>
>   Then this fact would make the whole Wapin bridge idea  untenable  
> as the front pin goes ... straight up toward the ceiling so how far  
> can the string climb a straight pin?

I'm sure if this were the unavoidable consequence of the Wapin pure  
vertical pin, we'd have heard about it in short order. So, no, I  
don't think it's a problem, although what we should be looking for is  
Wapin-bridge rebuilds whose downbearing has gone negative. I doubt  
there are any.

I'm going to have to back-pedal, here. When I made the comment about  
"strings having crept upwards........a regular part of the day", I  
was assuming that the issue hadn't been thoroughly debunked, and that  
climbing strings were something a large group of people swore to.  
("You can't tell me that it wasn't a flying saucer because you  
weren't there.")

I've never been happy with the explanation, well it has to go  
somewhere in all its excitement and it certainly can't go down, so it  
must go up the pin. Pins do jump when you bump them. You know they've  
jumped all they're going to 'cause when you bump them again, they  
don't jump. (This is something I actually see in the wire right by  
the front bridgepin, not something I hear and have to infer a  
location for.)

I've always assumed that they're most likely to wander laterally  
(away from the pin). I assume this because although the force require  
to drive them up 10 mils would be far less than that required to  
drive them over the same amount (adding to the side bearing), the  
friction required to hold them at that added 10 mils of deflection  
would be far less against the bridgepin than against the bridge top.

But that of course is assuming positive downbearing. Negative  
downbearing turns at least one thing on its head: the string's  
incentive to climb up the string. How much more likely, I don't know.  
As I said to Ron, you probably have to put several inches of negative  
crown into the board before the negative string bearing approaches  
anything like the side-bearing. At that point, a purely plumb  
bridgepin would be no help.

> If true down bearing exsists at the front bridge pin then what I  
> find more commonly is wire bends that need straightening rather  
> than tapping strings down on the bridge.

I take care of several heavily used pianos, and their strings all  
need "tapping over to the pin".

> If true down bearing really exists at the front bridge pin applying  
> some 3 to 4 lbs of down pressure per string at this point, how does  
> a string climb angled pins? I don't think they do. JMO

I don't think they do in the positive bearing scenario (said while  
back-pedaling furiously and coughing down crow tart). I don't know  
what they do in the negative bearing scenario. I'm just betting it'll  
be different from what they do in positive bearing.

I hope nobody says anything illuminating til tomorrow. I'm going back  
to my snooze.

Mr. Bill

"I gotta go ta woik...."
     ...........Ian Shoales, Duck's Breath Mystery Theater
+++++++++++++++++++++