overcentering justified?

[David Love]

Check the line magic line between the bottom of the key at the balance rail
and the whippen flange center pin.  If, at the key half way depressed, the
top of the capstan is on or close to the line, then I wouldn't mess with
the stack--especially because you already have clearance problems over the
rest cushion.  Try this:  put a small level on one of the unisons running
parallel to the strings.  Attach a small level (2" type) to the shank with
tape.  Raise the shank with a string hook until the bubble is at the same
position as the level on the string.  Since you have a hammer on the shank
of known bore distance (it should be less than 2" for this test), measure
the difference between the string and the top of the hammer when both
levels are equal.  Add the difference to the existing bore dimension and
that is the point at which the hammer will be 90 degrees to the strings
with the shank parallel to the string plane.    If the bore must be
shortened in order to get the proper blow distance and to get it to
regulate properly, then I wouldn't have a problem with that.  You can
adjust the rake in the following manner.  Bore the hammers to the dimension
you think you need for proper regulation.  Set a let-off rack to the string
height for that section using the end hammers as guides.  Dry fit the
hammer to a shank.  Raise the hammer to the string height gauge and while
looking from the side adjust the rake so that the hammer is at 90 degrees
to the let-off rack.   When you are sure you can get the angle you want,
apply glue (hot hide would be best here as it sets quickly) and adjust the
hammer for rake using the let-off rack as a guide.  Do this for the hammers
on the end of each section and then use a jig to align shoulders as normal.
If you are worried about the angle of inclination of the strings toward the
bridge, you can measure by placing a level on the keybed and one on the
strings to compare.  Use a protractor to see what number of degrees
difference there is by comparing bubble positions.   If the strings are
running uphill and you want to be exact about strike angle, adjust the rake
by the same number of degrees difference that you measured between the
keybed and the strings.  I can't say I would go this far with it.  I would
be content to rake the hammers so that they are at 90 degrees to the
keybed.  The angle of the strings upward toward the bridge is not likely to
be 3 degrees.  More likely it will be at most 1 - 1.5 degrees in the upper
treble and less as you go down the scale.  Who knows, if the board has
collapsed the strings might even be running down hill to the bridge.  And
that's assuming that the bearing is divided equally between front and back
which, of course, it rarely is.  And then, it depends on what the
definition of is, is.  Okay, that's enough...  

David Love
davidlovepianos@earthlink.net