[Ref. Larry Schuette, in 100214 MMDigest]

Larry,  The regulation on well-worn pianos changes over time due to
wear of the hammers and compression of the many felt pads.  Here is
a typical pattern:

 - The key dip increases due to compression of the front rail
punchings (with key depressed), and compression of the back-rail cloth
(key at rest).

- The let-off distance decreases due to compression of the let-off
button felt.

- The blow distance increases due to wear of the hammers and
compression of the hammer rest-rail cloth.

- The checking distance decreases due to increased key dip.  ["Checking
distance" refers to the distance from the hammer crown to the strings
when the hammer is "in check".]

Some of these wear issues may have been addressed by technicians who
serviced the piano in the past, but often the technicians make only one
or two adjustments.

An example would be when the technician reshapes the hammers to remove
string grooves, followed by touching up the let-off.  Occasionally
the technician will also touch up the lost motion.  But over time,
the other dimensions will change as described above, resulting in a
regulation which is far from the factory intent.  A rough analogy would
be to tune up an automobile engine but replace only half of the worn-out
spark plugs.

There are six principal components of regulation on an upright: key
dip, let-off distance, lost motion, hammer blow distance, aftertouch,
checking distance, and damper timing.

- Let-off can be set to 1/8 inch without regard to the other
components.

- Dip, blow, and aftertouch are tied together by the action ratio
(the effective levers of the key, wippen, and hammer assembly); these
three must be determined experimentally as actions differ somewhat in
the controlling dimensions.  Typical (starting) values would be:

  dip: 10.0-10.5 mm;
  blow: 45-48 mm;
  aftertouch: the jack clears hammer butt by 1 mm with key fully
  depressed and hammer checked 15 mm from strings.

The dampers should be timed so they begin to pick up at 1/2 blow;
earlier timing makes for touch that is heavier than necessary (for the
manually-played instrument), while later timing makes legato playing
difficult or impossible.

To set up the action properly requires going through _all_ of the
steps of regulation -- leaving nothing out!  An excellent step-by-step
procedure is described in Art Reblitz' book, "Piano Servicing, Tuning,
& Rebuilding".

John Rhodes, RPT
Vancouver, Washington