Bridge pin angles

[Ric Brekne]

Hi Phil

A couple things might be good to keep in mind whilst all these more 
abstract numbers scenarios are being tossed around.  Bridge pin angle is 
something that has been experiemented with by manufacturers through the 
years.  The present standards are more a result of experience with what 
actually works then a reliance on what in theory should work. And of 
primary concern has been holding a strong contact to the bridge in the 
face of even the strongest levels of play.

One only needs to look at the Capo bar and the classic Steinway forward 
duplex arrangement to see how much action is really going on at 
termination points. The constant battle to keep <<noise>> from  front 
terminations under control shows clearly the need for some kind of a 
clamp condition for the very mild angle the strings are offset at the 
bridge. 

The front edge of the bridge is going to get crushed because of a whole 
varity of factors.  The fact that the string is being yanked up and down 
violently non the least.  I've noticed very clear evidence that strings 
that are played more then others will display deeper grooves over time. 
I've also noted conclusive evidence that strings will dig significantly  
into the bridge cap without the presence of bridge pins, more then some 
might think.

One other thought... since you are interested in the numbers 
perspective.  Amoung the factors exerting a significant force upwards is 
that 1500 psi the bridge cap can take, which I assume increases with 
each tiny micron of compression in the wood.  With that at a maximum, 
the net force needed to break whatever friction levels at the pins is 
quite a bit lower yes ...?  Strings vibrating, soundboard vibrating, 
pins themselves vibrating,  all pretty violently seen from perspective 
of that exact termination point. 

For doubters... find an old beater and shave off about 2 mm of bridge 
cap, and replace with same thickness brass... carefully fitting around 
the front bridge pins to yeild the same termination profile as a new 
wooden cap. Re-string the spot and subject it to some concentrated use 
conditions for a half a year... bang on the string...vary the humidity 
over time.... etc etc.

Cheers
RicB


Phil Ford writes

Thinking some more about bridge notch crushing.  Aside from making the cap 
from some impenetrable substance, one way to reduce bearing stress at the 
notch edge would be to reduce resistance to the upward movement of the 
string.  This could be done by reducing side bearing angle and bridge pin 
angle.  If there was no side offset at all and the pin was straight up and 
down then it could easily slide as the bridge moved and the downbearing 
would be enough to keep it seated on the bridge at all times.  Of course, 
it wouldn't sound too good.  I wonder what lower limits would be?  Has 
anyone experimented with this.  I would think that establishing minimum 
sidebearing angle would be something that some piano company has worked 
on.  Is anyone aware of any numbers?  Bridge pin angle is something that 
seems less obvious as an item of investigation, but perhaps work has been 
done on that too.  Anyone know of anything?

Phil Ford