Action Geometry

Jon Page jonpage@mediaone.net
Tue, 06 Jun 2000 12:57:36 -0400


At 08:49 AM 06/06/2000 -0700, you wrote:
><snip>
>lower the hammers to proper blow distance, and then set the let
>off, (the hammers where now blocking after resetting the jacks).

The hammers were blocking because you increased the action spread
thus causing the contact point to be further out on the lever arm 
(repetition lever)
which increases the arc.

A place to start when determining action spread is to set it up so that the 
jack
is 90 degrees to the shank when aligned properly to the knuckle at rest 
position.
Also keeping in mind the line between the bottom of the b/r hole and wippen 
center,
the wip cushion/capstan contact point falls on this line when the hammer is
halfway to the string.

>At this point there was insufficient dip so that let off on most
>of the keys was barely possible only when pressing them down
>hard.  I proceeded to take the stack off and and add to the
>balance rail to increase dip, (there were not enough front rail
>punchings to remove to establish proper dip).  While I was at it, <snip>
>
>Rob Goodale, RPT


Before raising key height, make certain the sharps will retain a minimum of 
1/4"
depth onto the front rail pin. Less than that and the end of the pin will 
be digging
into the bushing during play.

Regards,

Jon Page,   piano technician
Harwich Port, Cape Cod, Mass.
mailto:jonpage@mediaone.net
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