Baldwin accu-hitch pins

[Ron Nossaman]

>Why?  Is it because it's a Baldwin?  Or is it because it's flat? 

Because it's flat, or more accurately too low impedance.



> Or is it because all other pianos have too much bearing?  Or is it
because there is
>some fairy dust that makes them allergic to excess bearing?  Maybe the
>casters need grease.  I want to know.  

Given a 600mm rib, 19mm high and 24mm wide (for example):
72' (21.95M) = 2.05mm crown  (Baldwin)
60' (18.288M) = 2.46mm          (Traditional)
50' (15.24M) = 2.95mm
40' (12.19M) = 3.69mm

The Baldwin rib in this case only has 83% of the crown of the "usual" 60'
radius. Using just the rib, it takes 3.05 pounds to deflect the 60' to the
72' crown height. To deflect these example ribs to 0 crown takes:
72' - 15.2lb
60' - 18.25lb
50' - 21.9lb
40' - 27.4lb

A higher crowned rib will support more load and still remain crowned. In
the area of the board where you might find this rib, at different bearing
angles you would expect to find loads this rib is responsible for to be
similar to this:

1.5° = 60lb
1° = 40lb
0.5° = 20lb  

The panel is under compression too, naturally, and will add stiffness and
crown. How much? Depends on how far you dried it down before assembly, how
thick it is, how dense it is, and how much bearing load is placed on it.
Bearing settings, successful ones anyway, will be determined by rib
dimensions, crown height, panel characteristics, and what you expect to get
out of the finished produce in sound. That's why comparing bearing settings
from one shop to the next isn't too informative.   
 

>What does the vertical hitch pins
>have to do with it?

Nothing.


>Does using vertical hitch pins on a non-Baldwin affect the decision on
>downbearing?

No.

Another caveat about pre-loading old boards by feel. Once you have it
wedged down where it feels solid and stiff, crawl underneath and check the
crown and see if it is already concave under load. The criteria for
replacing the soundboard is, or should be, whether or not it is still
structurally up to the job. 
 
Ron N