boring hammers

[erwinspiano at aol.com]

 Dear Stephane
  If you realize how much a millimeter difference can Make then be sure you bed the key frame first. Often the key frame is jacked up several mm's
  Ask me how I know.
  Dale





Hi beloved list.
I'm preparing to do another hammer change on an old piano, and I wanted to
pdate my (poor limited) knowledge about good hammer bore practice.
p till now, I decided bore length from difference between strings height
nd center pin height in each section.  I was surprised to see how far you
an go off by doing those measurements, and how much one millimeter does
ount here. So I was happy to read about this wonderful shortcut which is to
ry in each section a dry fit of a hammer with known bore length, and see if
t is perpendicular to string at contact time (really clever).  This gave me
lso opportunity to ascertain that certainly in the treble, the string
eight can differ by one or even two millimeters depending on where
recisely you measure it.  Of course it should be at strike line, but again,
ow do you do that accurately ?
ow, I have a few questions.  How do you set up your boring jig in order to
ake sure that the hammer molding is perpendicular to the shank (that is, if
ou aim for that) ?  The molding doesn't seem to have any parallel sides,
nd is asymmetrical of shape.  Also, for those tenor and bass hammers who
re bore with an angle, how do you calculate where the bit enters the
olding, in order for it to come out at the back approximately in the middle
f the molding (that is if you aim for that) ?
o you really adapt bore length at every section, or do you allow say one
illimeter offset in uniformity's sake ?
 read John D comment about the hammer shank length being fixed by design
nd so tweaking the hammer rake in order to get the perpendicular to string
it (if I got that right, John). In the ballpark that we play, is this
eally preferable to tweaking the hammer shank length and maintaining the 90
 rake ?
 also experience problems in doing a dry fit : if it is tight enough, it is
o difficult to move the hammer into its right position, while if it is easy
o move the hammer, it won't stay in its right position after the first hit.
as someone found a solution for this dilemma ?  I have considered gluing
he hammer simply like if it was to stay there, and then ungluing the usual
ay.  But maybe there is another less demanding trick ?
ll advise welcome, of course.  I'm mad about learning.
Best regards.
Stéphane Collin.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: https://www.moypiano.com/ptg/pianotech.php/attachments/20080424/0bf92c3a/attachment.html