Hammer Boring Angle

[Jon Ralinovsky]

List,
I've been thinking about upright hammer bore distances, and how there 
doesn't seem to be a set formula the same way that there is for 
grands (string height - hammer flange center pin height). 
Admittedly, I haven't spent any time with The Wippen and Key, so I 
don't know everything that's already been published.

However, based on the information below from Roger Jolly and some 
help from my dad, it sounds as if one could determine bore distance 
based on the existing rake, hammer center line to centerpin distance 
('hammer hanging distance'?), and string to shank center line 
distance (string to center pin distance added to the offset of 
centerpin and shank).  With this information, one can use simple 
trigonometry to determine bore distance.  The formula I have is: 
string to shank CL + hammer hanging distance * cos(rake angle).  For 
a treble hammer in one of the Hamilton uprights here, the formula 
would be
   2.25" + 5.0625" * cos (88º)
= 2.25 + 5.0625 * .0349
= 2.25 + .1767
= 2.42

This ends up being pretty close to the 2.5" that the hammers were 
bored at; I suppose that I can forgive the .080" difference between 
theory and reality.

Any feedback on this?

Respectfully,
Jon

>Hi Terry,
>               For max efficiency the hammer needs to strike the string at
>90 degrees.  The regulation parameters will help determine blow distance,
>Typically 1 3/4" to 1 and 7/8"  range.   Since the flange centre, is
>forward of the hammer shank line/ radius when the hammer is in contact with
>the string,  some rake is needed to maintain the 90 degrees of string to
>molding centre at contact.
>Same principal as over and under centering on a grand.
>Depending on turning radius, the length of shank and butt above centre,
>will determine rake.. eg.   Lots of rake on compressed console actions.  2
>to 3 degrees on the average upright.
>The bore distance,  combined with blow distance, will determine the
>relationship of the butt to the jack.  Too long a bore, you will have to
>set the back rail to the rear to obtain blow distance, and you can end up
>with problems with the jack returning and getting under the butt
>
>The jack contact point on the butt must be very close to horizontal.   This
>is not carved in stone because some actions have considerable toe.  (
>bottom of action is mounted in towards the plate.)   
>Now this leads into all the goodies associated with the key sticks.   OMG
>fudge factors creeping in all over the place.
>
>I have been working on a complete vertical series for the Journal, but have
>only completed the first 40 pages.
>
>  Now to cut a long story short duplicate what is there, unless some thing
>is obviously wrong.   <G>
>
>Just some random thoughts.
>
>Roger
>

-- 
Jon Ralinovsky
Piano Technician
Department of Music
Miami University
513/529-6548