Grand backchecks

[David Love]

Longer backchecks are not the answer.  The tail checks on only a small area
of the backcheck.  A taller check won't make any difference if the
backcheck height and angle are already correct.  Look to see that the tail
is radiused properly.  If the leading edge of the tail is contacting the
backcheck first, then either the angle is backcheck angle is to acute or
the tail is not properly radiused, or both.  When in check the lower 1/4"
of the tail should be in contact with the check.  If only the very tip is,
then you will have to increase the tail arc with either a hammer shank
clamp and a disk or mini belt sender, or by removing each hammer or your
method of choice.  The radius should be not more than 2 1/2" and the
backcheck angle of inclination should be about 20 degrees off vertical.  
At let off, the bottom of the tail should be 1/16" above the top of the
backcheck at a line drawn parallel to the keybed.  Be sure that the tails
are slightly roughed (80 grit paper is enough, checkering files are
overkill, IMO), and, of course, the leather must be in good condition with
not little ledges cut into it.    

David Love
davidlovepianos@earthlink.net


----- Original Message ----- 
From: Tom Driscoll 
To: pianotech@ptg.org
Sent: 7/29/2003 8:49:53 PM 
Subject: Grand backchecks


List,
            I performed some regulation on an older Baldwin L today. This
action was rebuilt with all new action parts two years ago by another tech.
and needed routine regulation to put things back in order. 
            The problem is with the checking. On a light blow the hammers
are bouncing off the top of the backchecks. The rep .lever springs are
adjusted correctly, key dip, blow, and after touch are all fine. Hammer
tails are well prepped also. Changing the backcheck angle helped somewhat,
but the symptom persists. The backchecks are 1 ¼ “ long and I’m thinking
that a longer backcheck is necessary.
            I see in the pianotech catalog an “old” Steinway backcheck
listed.
            Advice appreciated.
            Tom Driscoll