Yamaha Spring Tension

[Frank Emerson]

I had a new vertical action that was double striking the strings on a very
light blow.  The problem turned out to be a combination of too much
aftertouch, and too weak hammer return springs (of the type with the cord
loops).  You cannot rely on the angle of the spring to be a gage of its
strength.  Overly compressing the spring to disengage the loop can rob the
spring of half of its strength.

I prefer to measure the springs strength at the hook of the spring, itself,
rather than at the flange.  40 grams measured at the spring is roughly
equivalent to 20 grams measured at the flange.  It's somewhat analogous to
measuring lengths with a scale marked in 1/32" increments vs 1/16"
intervals.  Besides, it rules out the friction in the flange center,
insignificant though that may be.

In the above case, the springs measured at the spring hook measured about
20 grams, while replacement hammer butts for the same piano measured about
40 grams.  Reducing the aftertouch and bending the springs to return about
40 grams of tension resolved the problem.  

Frank Emerson


> [Original Message]
> From: Jon Page <jonpage at comcast.net>
> To: <pianotech at ptg.org>
> Date: 6/28/2007 7:26:55 AM
> Subject: Yamaha Spring Tension
>
> I'm replacing the cords on a Yamaha vertical. What should be the
> spring tension as measured with a Correx gage on the flange?
>
> Nothing surfaced in the archives.
> -- 
>
> Regards,
>
> Jon Page
>