[pianotech] butt plates

[David Nereson]

     Not sure what you're talking about.  Butt plate screws are accessible
from the back of the action, in between the damper levers, not the front.  The
screws that hold wooden flanges or Billings flanges to the action rail are
the (butt) flange screws, not butt plate screws.
     Butt plates are found in two types of upright actions:
     1) old upright actions that have brass rails fastened to the main
action rail -- see bottom of page 134 in the Schaff catalog.  These brass
rails have tabs, or tongues that stick up vertically, with a groove in them
for the center pin.  A butt plate (approximately 1/8" x 1/2",  or 4 x 12
mm) clamps the center pin to the tab by means of the butt plate screw,
which is quite small -- about 2 or 3 mm in diameter by maybe 10 mm long --
much much smaller than the wood screws for wooden flanges.  Also, it's a
machine screw (not tapered like a wood screw).  You need a long narrow
screwdriver to access these.  A small screwdriver with a 1/8" wide blade
and a shank not much thicker will work, but the so-called Kimball
screwdriver in the Schaff catalog, page 40, #4106, is better.  The brass
rail is threaded and the screw goes in from the rear (damper side),
although there are some oddball actions where the butt plate is threaded.
     There are also screws that hold the brass rail to the action rail.
These would have to be extremely loose to cause any malfunction in the
action.  To tighten these, yes, you usually have to  push the jacks to the
side.  They'll usually yield enough, but be careful -- you could break a
wippen flange if you push them too far.

     2) some (usually) Asian uprights (Yamaha) that have Schwander-type
butts, where the hammer return springs are part of the butt assembly and
are retained by a loop of thread fastened to the butt flange.  Some of
these have "standard" wooden flanges with a full circular birdseye, and
some have only a semicircular birdseye with a butt plate.  Again, you
tighten the butt plate screws from the back, between the damper levers.
This type of butt also has a flange screw that holds the flange to the main
action rail.  The flange screws can be tight, but if the butt plate screws
are not, the hammer can still be wobbly and the center pin can "wander," or
work its way out of position.

    For "regular" flange screws on wooden or Billings flanges, you use an
action screwdriver -- Schaff # 34 or 35, page 41.  You nudge the jack aside
with the tool and the lip or edge or notch or inset or whatever it's
called, helps hold the jack out of the way.  There used to be one available
where the rear notch was flared, rather than a right-angle notch, which
prevented snagging  the jack when removing the screwdriver, but I don't see
it in the catalog.  You could modify #35 by filing down the sharp corners
on the "back edge" of the blade.
    With either type of butt plate, if the screw or plate is missing, the
entire hammer assembly will be about ready to fall off and so wobbly it
won't function.  Yes, there's a little nub on the brass rail that helps
(not much) position the butt plate in place.  You also need a butt plate
inserter, Schaff #128, page 53, for holding the butt plate in place while
you get the screw started.  This is done before you position the butt onto
the tab of the brass rail.  You have to feel the center pin "snap" or
"click" into the groove on the tab, before you tighten the screw.
      Hope all this helps.  Still not sure exactly what problem you're
having, unless it's an oddball action with some screw/butt plate
arrangement I've never seen.
     ---David Nereson, RPT
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