First you should know that no hammer comes from the factory with a tail
shaped the way it will stay once it is in use in the piano.  It does
not matter what the shape of the tail is when you get it.  You are
going to shape it to best catch the backcheck without a bump.  By bump
I mean the feel at your finger when the hammer tail contacts the
backcheck.

Many hammer replacements are not shaped when they are put on.  These are
put on either by amateurs or by a technician who is not a pianist and
who does not realize why pianists then say that grand plays like a
tractor.  Or it was done by a piano company that is saving the money it
costs for a technician to do it right.  A trained pianist will play a
measure or two and know that the action feels clunky.  These are terms
I have heard from pianists who do not know what causes it.

You must understand that the hump on the tail that comes from the maker
must not stay.  When that hump hits the backcheck, 1) it gouges holes
in the backcheck over a couple of years, and 2) it causes an impact that
is felt by the pianist as a clunk.

There is also a similar feel when the damper stop rail is not far enough
down.  In that case the key-back goes up on a mezzoforte or forte note,
and the damper keeps going, hits the stop rail, and then drops back
down to hit the damper-lift felt on the tail of the key.  This is also
interpreted as a clunk by the pianist.  Dampers should have their stop
rail screwed down tight in a position such that, when you hold any key
down, you cannot pull the damper up more than just a hair.  Also, the
stop rail must be high enough that pushing the key all the way down
does not press the damper lever up into the damper stop felt.

Anyway, the hammer tail is shaped before I install the hammers, because
taking out each flange screw and shaping once installed is more work.
Keep an upright shank next to the set of hammers and the belt sander.
I use a small, one-inch belt sander.  With the shank in the hole, the
hammer tail is thinned down on the sides until the tip is only about
1/4" wide.  The sides should be parallel with the shank sides.  The
back or surface of the tail that contacts the backcheck is then sanded
down perpendicularly square to the shank and its hole.  Then the tail
is sanded to the smooth arch form felt to tip.  It is not the cutesy
curl found on some, but a slight arch.  This is the shape found on the
original expensive brands of piano.  To get the shape right, I hold the
flange steady and move the hammer against the sanding belt in the same
arc it makes in the piano.

I will try to take some photos of this process and post them in the next
few days.  I may have some already, if I can find them on my disk.

The idea is to have the hammer come down from hitting the string, and
slide down the backcheck leather to a smooth stop.  With a sharp curve
or the hump from the factory, you will get the tail impacting the
leather, with a resulting bump felt by the pianist's fingertip.  My
method has the tail mirroring the shape of the backcheck and slowing
to a stop -- which is not felt at the key.

If you want to know more about my technique for regulating grand
actions to satisfy all sorts of concert pianists, get a copy of the
book by Danny Boone on grand regulation and voicing.  But be prepared.
I had a long-time technician read it, and his comment was, "I did not
realize there was so damned much to regulating a grand piano."  He has
been a technician for around 50 years, and he still learned a lot.  I
learned my technique from Danny Boone back in the 70's, before he wrote
the book.

You must remember that our reproducing pianos are being played by the
world's finest concert pianists.  If the piano is not in the same
condition as the piano in a concert hall, we will not get the musicality
that is actually in the rolls.

By the way, I would never use anything but Renner Blue hammers for a
piano from the American piano era like your Ampico.  While Abel makes
good hammers, they have tended toward the thin sound when I have used
them.

D.L. Bullock,
St. Louis, MO
http://www.thepianoworld.com