Key Leads and Inertia

[John Hartman]

Ron Nossaman wrote:

> Del,
> You knew this was coming, so I won't make you wait any longer. Do you 
> have any rough rule of thumb go - no go diagnostic criteria for deciding 
> when keys are too flexible during teardown?
> 
> Ron N


Ron, I hope you don't mind if I weigh in on this. I use a 1000g weight 
applied to the end of the key (naturals). If the weight bends the key - 
measured with a dial indicator - more than 1mm I consider it to be a 
problem, ideally is should be under 0.75mm. The key is removed from the 
key frame and placed on a work bench. The key is supported under the 
balance rail hole and under the capstan. A clamp is place to hold the 
key down near the capstan. The weight dangles from a cord off the 
playing end with an indicator close by it. The weight is slowly lowered 
and a reading is taken. Average several reading to find the key flex.

I derived the 1mm using data in Pfeiffer's book "The Piano Hammer". 
Using the force applied to the key during load play I came up with a 
figure that would bend the key 10mm. This along with personal experience 
led to my rule - no more flex than 1mm at 1000g.

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]