[pianotech] Grand Backcheck Geometry

[Paul McCloud]

Jim:
Check out Bill Spurlock's "Using the Grand Hammer Tail Jig".  In the instructions, there are very specific directions for radius of the tail (the purpose of the jig) and what constitutes the proper relationship with the backcheck.  I think he has these instructions for sale on his website www.spurlocktools.com.  I will not reproduce it here, for obvious reasons.  You will not be disappointed.
Paul McCloud
San Diego

----- Original Message -----
From: jim at grandpianosolutions.com
To: "pianotech" <pianotech at ptg.org>
Sent: Tuesday, February 28, 2012 7:08:22 PM
Subject: [pianotech] Grand Backcheck Geometry

Lets try that with a more focused example.

In determining the radius of the hammer tail for a grand is 2-1/2 -3" .  
WNG uses an even tighter radius, 1.5" I think.   Why?   THe pivot for 
the shank is at the flange, not 1/2 or 3/4  out on  the shank.

This is presumably to deal with the radius described by the backcheck as 
it swings into full key dip, to avoid interference.  So my question 
(more focused-ly) What is the geometrical relationship between those two 
arcs?

Jim Ialeggio


-- 
Jim Ialeggio
jim at grandpianosolutions.com
(978) 425-9026
Shirley, MA