Bridge Pins & Nega Bearing, was Re: Why do we need crown?

[william ballard]

We have to examine the effects of negative string bearing carefully.  
Agreed that yes, bearing and crown are independent conditions,  
sometime coincident and sometimes not.

And also, as the board and strings are combining to form a balanced  
pair of opposing springs, neither of them particularly care who's on  
top. With positive crown and positive downbearing, the board will  
resist being pushed down by the strings and the strings will resist  
being pushed up by the board. With negative crown and negative  
bearing, the board will resist being pushed up towards flat and the  
strings will resist being pulled down away from flat.

In either case you get a pair of balanced opposing springs. But that  
is a separate matter from whether the bridge pins prefer positive or  
negative bearing (which as we know can happen regardless of whether  
the crown is above or below flat).

With positive bearing on the bridge, this force doesn't stress the  
pins much at all. The bearing force simply side-steps the strings and  
presss down on the bridge. (Side bearing is another matter but not a  
part of this discussion on the effects of baring on the bridge pins.)  
However when any bridge pin drilled an an angle (and that's most of  
them) finds the bearing  turned from positive to negative, it will  
now find it prying upwards on the pins in a menacing fashion.

Positive bearing strings will stay seated just as well with positive  
crown as with negative crown. It's negative bearing strings which  
won't stay seated and which apply their force to destroy the pinning.  
That's regardless of positive or negative crown.

On Apr 23, 2006, at 4:02 PM, Erwinspiano at aol.com wrote:
> Not so  with the reverse crowned board.  I have worked on my share  
> of intentional reverse crowners & although the board is under a  
> positive downbearing load the pins do not have any more trouble  
> staying seated than the conventional system. The board is under  
> tension but in my expereince with less adverse affects than the  
> boards built ....the other way
>
>>  Then too... in the grand it seems like we have trouble enough as  
>> it is
>> keeping strings seated to the bridge. Downbearing or no... with the
>> panel countercurved as it were it would seem to me that the strings
>> would find it even easier to become unseated.
>> Cheers
>> RicB

Mr. Bill