[pianotech] problem in mating hammers to strings

[David Nereson]

    I feel to see if all the strings are in the same plane.  I 
don't like the idea of the bubble level because if the floor 
isn't perfectly level and the plate isn't perfectly level, or if 
the holes in the agraffe aren't perfectly level, you're getting 
a false indication.
    But regardless, when viewing the hammer line at the strike 
point, it should appear as a straight line, so that's how I 
filed them.  I then held hammers against the strings, plucking 
the strings, and still found indications that the hammers had 
high areas, or that a right string was low, and again, almost 
all in the low tenor, and all on the right side of the hammer. 
So I used the plexiglass paddle with a thin (3/16") strip of 
sandpaper glued to it, as demonstrated by either Andre Oorebeek 
or Ben Gac, I believe, to file down the hammer in the area that 
damps the strings that don't ring when plucked.
    This results in hammers that have a "step" in the strike 
point surface, but using the end of a steel rule and a bright 
light, I did not observe any low ("unlevel") strings in the 
corresponding unisons.  I still wonder if the pressure of 
holding an angle-bored hammer against the unison causes the 
shank to flex or the hammer to lean.
    --David Nereson, RPT