evaluating sdbd. crown & bridge downbearings in a new piano

[Brian Trout]

Hi Ron,

Gee, I hope I'm not sticking my nose into a place it doesn't belong, but I
had a thought as to how you might determine if a board was rib crowned.

If you look at the grain of most ribs, it'll be pretty straight.  If the rib
was machine crowned, I would think you would see 'end grain' popping up
along the length of the rib on the side that was glued to the soundboard.
(Assuming that the board is out and the rib is off.)  Not real easy to see,
but I think it could be done.  Also, you could likely see some of the grain
lines on the side of the rib.  That would also likely give a clue or two.
Using the back of the rib (the side fartherest from the glue joint) could be
deceiving, since not all of them were the same.  Some used ribs of the same
thickness from end to end, and some used ribs that were machined on the top
and flat on the bottom.

But you probably already thought of all of this stuff long ago... :-)

Have a good day,

Brian Trout
Quarryville, PA
btrout@desupernet.net

----- Original Message -----
From: Ron Nossaman <nossaman@SOUTHWIND.NET>
To: <pianotech@ptg.org>
Sent: Tuesday, September 28, 1999 9:07 AM
Subject: Re: evaluating sdbd. crown & bridge downbearings in a new piano


> >The only way to tell for sure (that I know) is to examine the old ribs
after
> >the old soundboard is removed.  Measuring ribs in place may give some
clues,
> >but would probably not be conclusive.
> >
> >Frank Weston
>
>
>
> Well, now I am confused. I thought you had another shop do soundboard work
> for you, or am I mistaken? I'm still wondering how you verified that none
of
> those old Knabes had crowned ribs. Do you get the old board back with the
> piano when it returns from the rebuilder? Even with the old board at hand,
> what sort of evidence do you typically look for to determine what crowning
> system was used? Since any type of rib that has been subjected to bending
> forces of any kind for 50+ years will take a set, what do you look for
that
> will conclusively tell you what the original top profile of the rib was?
> Please explain. This hasn't come up before, and I would really like to
know
> how it's done.
>
>  Ron N
>
>