Downbearing Error - solution

[David Love]

John:

Installing a plate float system is definitely a nice thing to have for
tweaking bearing after the fact.  Precalculating the bridge height
(trigonometry does come in handy sometimes) from a straight string stretched
between the termination points forward and aft also helps as does installing
vertical hitches which can also be adjusted.  Calculating the soundboard
deflection (easier on a rib crowned and supported board) also gives more
data with which to ensure the bearing comes out close and helps to prevent
these kind of mishaps.  Of course, they are usually represent modifications
to the original which provides a psychological challenge to some--but not
all!   

David Love
davidlovepianos at comcast.net 
www.davidlovepianos.com

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of John Formsma
Sent: Tuesday, November 20, 2007 2:33 PM
To: Pianotech List
Subject: Re: Downbearing Error - solution

On Nov 20, 2007 3:55 PM, Richard Brekne <ricb at pianostemmer.no> wrote:
> Hi folks
>
> After a restless night thinking about the prospect of recapping I
> remeasured my string offset angles today and calculated out that I have
> about 2.5 degrees in the high treble and just over 1 degree in the
> bass.  Not quite as bad as I had thought after all.... but still too
> much.  As it turns out I can get down to just over 1.3 in the top and
> close to 0 in the bass by taking a piece of 5 mm thick hardwood (the
> sticks they send with shanks from Renner as it turns out) and form them
> to match the contour of the plate just in front of the hitch pins.
> Fashioning a string rest with some thin felt brings up the back length
> to levels that I can easily live with.

Ron Nossaman would be a better commentator on this.  But when I was in
his shop, he showed how he sets the plate level.  Pretty nifty.  I
think it's been on the list before, and maybe even a Journal article
by Del some time back.

You can reset the level by turning up a nut on a threaded rod type
thing - even at tension. (Forgot exactly what it's called.)  It's what
I'll do when I get around to rebuilding.
-- 
JF