Key Leads and Inertia

[John Hartman]

Delwin D. Fandrich wrote:

> Most of the energy lost between the key end and the hammer goes into bending
> the key. At action saturation the front of the key fully bottoms before the
> hammer starts to move. I'm not sure how much key leading contributes to this
> but I shouldn't think it was all that much.
> 
> Del

Del,

Your article on this topic in the Journal brings a new perspective to 
how the action work. It seams like we are hell bent on calibrating 
static balance and action leverage with out putting it into proper 
perspective. Placing a tiny piece of lead it a key to achieve a balance 
of 38g instead of 39g or making sure that all of the knuckles are in a 
line to achieve a particular leverage seems overly picky and unnecessary 
considering the magnitude of issues left unattended. These static 
particulars are only relevant if the piano is played very softly. Once 
the action gets up to speed (accelerated) inertia and compliance become 
far more important.

In order to improve action efficiency I have been installing stiffening 
top plates on actions with longer keys. I have done this on several 
Steinway model Bs with good success. This seems to extend the dynamic 
range while using a relatively soft light hammer (lighter hammers are 
more efficient because they have lower inertia and bend the shank less).

You can test the compliance of a key by measuring how much it bends with 
a known weight pulling down on the front end. Using this method I have 
been able to ascertain which actions need this treatment. The 
accelerated actions with all the leads near the balance rail are 
particularly weak. Short keys are usually stiff enough.

I made the plates from 5mm maple and spruce (spruce in the high treble 
only). New maple key buttons are installed as well. Longer .062" concert 
grand key pins are installed (Pianotek). A new key stop rail needs to be 
fashioned to provide clearance for the fallboard. Along the same lines, 
when I make a new keyboard for the Model D I use maple and spruce for 
the top plates - not soft basswood usually seen here (some don't even 
have top plates).

View the photo on my wed site here:

[link redacted at request of site owner - Jul 25, 2015]


John Hartman RPT

John Hartman Pianos
[link redacted at request of site owner - Jul 25, 2015]
Rebuilding Steinway and Mason & Hamlin
Grand Pianos Since 1979

Piano Technicians Journal
Journal Illustrator/Contributing Editor
[link redacted at request of site owner - Jul 25, 2015]