[pianotech] Bobbling hammers and jack spring pressure?

Jurgen Goering pianoforte at pianofortesupply.com
Thu Jan 22 10:10:27 PST 2009


Gregor,
you have had a lot of good advice and things to look for.   I would 
like to add two more things, although I do not think they are humidity 
related:

You say the player senses increased resistance deep near the bottom of 
the key dip.

1) Front rail punchings:  One thing could be that the front rail 
punchings are thing and spongy.  When  testing  for after touch, a 
technician will often press the key right down to the bottom so it is 
resting solidly on the front rail punching.  When  player is playing 
moderately, a front rail punching which is not firm enough will give 
the player resistance up to and over 1 mm before the key is really 
bottomed out.  Result: the hammer bobbles.  As a test for this you can 
remove one front rail punching and set key using only cardboard 
punchings.   Set dip to the specs and see if the hammer still bobbles.  
If it does, the front rail punchings are not firm enough.

2) Balance pin holes in the bottom of the key:  if the thickness of the 
wood at the bottom of the key at eh balance pin hole exceeds 3 or 4 mm, 
  the player will encounter resistance near the bottom of the keystroke. 
  Test for this by removing the action and the FR punching on one key 
and slowly depress the key to feel for resistance at 10 mm dip - there 
should be none.  If there is, use a balance hole reamer (JD would 
correctly  say counter-bore) and remove material from the inside of the 
balance pin hole from the top


Jurgen Goering
Piano Forte Supply
(250) 754-2440
info at pianofortesupply.com
http://www.pianofortesupply.com

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