Setting bearing: was Component Downbearing Gauge

[Ron Nossaman]

>So this creates an effective multiplier for calculating height of a string
>above the rear string rests at the point when the stretched string just
>touches the front of the bridge.  For 1 degree, multiply the rear string
>length in inches by .018; for 1.5 degrees, by .027; for 1/2 degree by .009;
>etc..

Yes, but the multiplier has always been there, long before the gage. In 
Excel, sin(radians(1))=0.017452, sin(radians(1.5))=0.026177, and 
sin(radians(0.5))=0.008727.


>The other challenge is deciding how much bearing one should have in
>a given section.   This seems to depend on the amount of available crown
>and the relative stiffness of the board.

Or at least it should, as well as the free back scale length. We see plenty 
of examples in the wild with no obvious evidence that any of these factors 
were even briefly considered.


>What is the best way, I've often
>wondered, to calculate the amount of deflection that is likely to occur on
>a given board under so many pounds of downward pressure--we're talking
>about new and old boards.  If you knew that, then it would be easier to
>figure out the amount of bearing.

Yes it would. Loading the board with a few wedges under plate struts is 
probably about the best we can do with both an old board and a new one 
copied from the original. Even so, we only get an indication of how stiff 
the board is at that moment, which is no predictor of how it will be next 
year.


>However, I've also heard several
>perspectives on this, from the goal of achieving a deflection of 1/2 the
>available crown, to flattening the board entirely.  I'd be interested to
>hear comments on this.
>
>David Love

It depends on the board, it's design and general condition, most of which 
we can only guess at when we're deciding what to do. I would however, 
disagree with anyone who says that a "conventional" soundboard that has 
enough bearing on it to push it flat is a viable system. Manufacturers say 
"you can't tell the condition of soundboard crown with the piano strung", 
which I consider to be nonsense. That's precisely when you can tell the 
condition of the crown and load capacity of the soundboard. Techs who don't 
do belly work say "it's the sound that matters, not the crown". Which is 
essentially true except that these folks so very often don't seem to hear 
or consider objectionable, the sounds indicating soundboard problems. Like 
the manufacturers, "it's the sound that counts", but when it sounds lousy 
and the board is concave, then what?

It's always been interesting and frustrating to me that while we all would 
like one or two simple checklist rules that universally apply, it doesn't 
work like that. There dozens, if not hundreds, of decisions either made or 
allowed to happen without notice or consideration that make up the 
cumulative effect. We've discussed a lot, probably most of these things a 
number of times in some detail on the list. It's a big subject for as 
simple as it is, and everything depends on most everything else.  So how 
much bearing should we put in what section of what specific piano? Whatever 
sounds best.

Ron N