Key Friction

[Stéphane Collin]

Hello Ric, Terry.

Ric wrote :


> How do you check for key friction btw.  Not so common over here to take 
> (DW-UW)/2

Well, like you said, I put a clip lead on the backcheck and measure 
(DW-UW)/2. Is there a better technique ?

This way too you can point out regions where friction arises, for example 
when the key moves definately with a certain weight, but doesn't go all way 
down the dip : I check then for small discrepencies of bushing thickness 
inside the mortize, or glue bubbles.  When there are no more problems at the 
bushings, the only place left for friction is the balance, like when there 
are too many and/or too hard paper punchings under the cashemire, or maybe 
fulcrum issues, like when the notching at the balance pin is damaged (or, at 
least so did I think, when the contact line between the key and the balance 
rail is not exactly perpendicular to the balance bushing mortize, like in 
dogleged keys).
I feel that what is desired here is 1° evenness from key to key and 2° least 
possible friction without compromizing the firmness of the key movement. 
Friction at this level only slows down the movement of the key.  But 
pianists often do, at the same time as the vertical movement of the fingers, 
some horizontal movement of the hand, causing, if too much play at the front 
bushing, undesirable noise (like exacerbated when you run your hand quickly 
from left to right over the keys) and worse : loss of energy dissipated in 
this shock, together with the feeling of running a sprint with 45 shoes when 
your size is 42.  Same if the balance bushing is too loose : on a hard blow, 
the key will wobble upward a bit, dispending useless energy.  This is why I 
kind of like the very tight balance holes that you find in older Bechstein 
pianos : the tight hole doesn't cause that much friction (far less than 
thight bushing, where the friction force is amplified by the lever) but even 
on a forte blow, the key remains in contact with the balance rail.  Minimal 
noise, maximal energy transfer, and you can ease the balance bushing until 
just before the moment you can see the backcheck move from left to right 
together with your finger (but opposite) at the front of the key.

What do you think ?

Stéphane Collin.