Key Leads and Inertia

[Delwin D. Fandrich]

----- Original Message -----
[link redacted at request of site owner - Jul 25, 2015]
To: "Pianotech" <pianotech@ptg.org>
Sent: Thursday, May 01, 2003 2:26 PM
Subject: Re: Key Leads and Inertia


> 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, 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


That sounds about right. Feels about right, too. Keeping in mind that keys
vary considerably from one another. Especially those cut by drunken sailors
back in the good old days. I tend to look for the thinnest keys. And the
most bent keys.

Del