[CAUT] left to right or R to L?

[Fred Sturm]

On Nov 12, 2008, at 3:37 PM, Ron Nossaman wrote:

> If your board has any real crown, and you're putting any real  
> bearing on it, this will happen.


My last post (which for some reason was labeled as SPAM?? 59% - I must  
have cooties or something) was somewhat tongue in cheek. On a more  
serious note, my remark about bridge pins hitting struts had a couple  
of scenarios behind it.
	The first was a local rebuilder who believed that "more is better,"  
so for every piano he rebuilt he increased both crown and downbearing.  
He started by "re-crowning" the board: took a sabre saw and cut a kerf  
in the soundboard about 6 inches either side of the bridge. The kerf  
extended about halfway through the ribs. He jacked it up from  
underneath with wedges, inserted hard wood wedges in the rib slots,  
and shimmed the board. "Very successful process": run a string under  
his boards, and you see a gap of as much as 1/4". To increase  
downbearing, he lowered the plate 1/8" or so.
	As a result, he often had the problem of bridge pins touching struts,  
and colleagues tell me he sometimes would have to "jack the board  
down" (wedges or jacks pressing down on the board) to be able to  
restring, and that didn't always work. Sometimes he'd have to remove  
wood from the bridge or file a strut.
	The second scenario is manufacturing. Crown varies by moisture  
content, especially for compression crowned boards. The manufacturer  
(or rebuilder perhaps) takes a lot of care with moisture content in  
gluing on ribs and installing the board. But then attention seems to  
wander. The rim with belly wanders around having things done to it,  
and eventually gets to the guy who "sets the downbearing" by setting  
the plate and planing bridge tops (vertical pinned plates are  
different, but not entirely). Is the factory humidity controlled? Not  
generally. Are the soundboards checked for EMC when downbearing is  
set? Not generally (Here vertical pinned plates become the same as  
other models).
	The point being that often, in many manufacturing or rebuilding  
processes, nobody knows where the soundboard is when downbearing is  
set. Is it dry and flat? Moist and super-crowned? Beats me, says the  
factory worker. I just do my job.
	So it really becomes anyone's guess whether bearing was established  
in a moist or dry period. We get to the stringing department.  
Sometimes they have a piano where the bridgepins are hitting the  
struts. Hmmm, that's funny. Well, we'll just develop a procedure for  
that. And they do.
	IOW, one hand doesn't know what the other is doing, one department  
doesn't communicate with the other, nobody really thinks through  
whether the manufacturing process actually reproduces the design.
	To my mind, bridge pins hitting struts should wake someone up to ask  
a question or two. That's the point I was trying to make. Now it may  
well be that a particular design philosophy would find that scenario  
acceptable, and that's fine by me.

Regards,
Fred Sturm
University of New Mexico
fssturm at unm.edu