Down-Bearing for Old Board

[Farrell]

Thanks Ron. You kinda reiterated what Brian Trout had said to me. But now
after hearing the same thing (or variations thereof) from several different
sources, I think all this is congealing in my mind. I think I can fiddle
about with it, look at existing crown, and feel comfortable with where I am
going (or at least know where the TOO MUCH and TOO LITTLE endpoints are).
I'm glad you replied. Thanks. Now I can go about the task at hand. Scary to
think, isn't it!  ;-)

Have you ever read Reblitz on this stuff. WONDERFUL resource, BUT! The
method presented for setting bearing is to look at the downbearing at the
agraffe/capo bar. I tried that. Wooooooooaaaaaaaa. Bad news. Downbearing at
the backscale is the prime area to look it think, but also to keep in mind
the angle of the bridge top (make sure the little rascal is in the same
plane as the average string plane, such that there is a little front bearing
and the back bearing.

The list. What a resourse! Thanks folks. I look good with help from you'all!
:-)

Terry Farrell
Piano Tuning & Service
Tampa, Florida
mfarrel2@tampabay.rr.com

----- Original Message -----
From: "Ron Nossaman" <RNossaman@KSCABLE.com>
To: <pianotech@ptg.org>
Sent: Friday, February 02, 2001 7:45 PM
Subject: Re: Down-Bearing for Old Board


> Hi Terry,
> I've just put an exceptionally lumpy ugly week to bed (I hope), and have
> about a nickle's worth of life left - so I figured I'd just as well spend
> it here.
>
> Generally, I'll load an old board less than a new one, especially a
> compression crowned one. If you had all this crown after drying the board
> down to shim, it almost has to be rib crowned, and you can probably get
> away with a little heavier bearing load. Dale's description of pre loading
> with wedges is a good guestimation method. I'd also suggest crawling
> underneath with your Kansas Straightedge (string) and checking how much of
> the available crown there is (everywhere you can reach, rather than just
at
> the longest rib) before and after the pre loading. When you've determined
> that you have enough crown after pre load that the string bearing you will
> set won't push the board concave, you're there - or at least not past
> "there". Note here that ending up with what you might consider "perfect"
> bearing angles over a reverse crowned board is a counterproductive
> approach. Also, be aware that bearing works with angles, not projected
> string height at the back scale termination point, so you have to factor
in
> your backscale length when you're playing with the string and measuring
> plate or aliquot height. The absolutely wonderful thing about doing this
> stuff is that if you don't set more bearing than the crown can
accommodate,
> it's pretty hard to screw it up. The bearing pressure changes quickly as
> the angle changes, so as a strung piano is pulled to pitch, the board
> deflects and offers more resistance as the bearing angle decreases and
> produces less downbearing force. The forces will balance in the middle at
a
> point pretty close to where you intended when you set the thing up, even
if
> your guestimation was a little rougher than you had hoped. The silly thing
> will meet you half way and try it's best to not let you mess it up, which
> is probably the only reason most of us were able to piece any sort of
> workable bearing setting procedure together in the first place.
>
> An alternate method is to weight the bridges, measure deflection, add more
> weight, measure deflection, and determine the deflection response curves
of
> different sections of the board. Then, from the string scale, compute
> optimal finish string bearing in each section that will leave the board in
> whatever state of deflection you decide you want (balancing bearing load
> against deflection curve), and calculate the bridge/plate/aliquot heights
> accordingly, averaging as necessary to accommodate the different backscale
> lengths.
>
> Whatever works best for you.
>
>
> Ron N
>