Downbearing

[Farrell]

Hello Listies. I am refurbishing two very small, very cheep grand pianos.
Soundboards have been shimmed. Both have good crown (1/4" or so). Bridges
will be repinned (pins set in epoxy) but not re-capped. Plates are out of
both pianos. I will be able to adjust the height of both plates a bit. Both
pianos have treble bridges that are highest (most downbearing) on the two
ends and lowest (least downbearing) near the center (high tenor/lower
treble). My plan is to determine an ideal amount of downbearing in the
various sections and shave off a little bit of bridge top to achieve those.
I have some good info on downbearing for new soundboard, but I do not have
good info for old soundboards. I think (maybe) in general downbearing on an
old unstrung soundboard should be about half to two-third that of a new
soundboard.

Reblitz suggests 1/32" on the bass bridge and 1/16" to 3/32" on the treble
bridge, tenor to treble. He measures downbearing at the forward termination
though (agraffe, capo, etc.). I have been taught to measure at the
termination point behind the bridge. That seems like a very small amount
measured way at the other end of the string. What does anyone else use for
guidelines in a situation like this?

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