Shanks parallel to strings- off list

[Phillip Ford]

>
>Hi Phil

Dean,
The post is labeled off-list, but it came to me over the list, so I'm 
responding here.  Nothing too shocking here I think, and I thought 
there might be something in here of interest to the list.

>
>If the bat is mounted rigidly, then it doesn't matter where the ball hits
>it. Any point on the bat will give equal rebound. I think the problem here
>is one of perception: you seem to be primarily considering the effects of
>the speeding ball coming to the bat. But we have two things to consider: the
>energy the ball adds and the energy the bat adds. For the energy the ball
>adds, you are quite right: it doesn't matter where on the bat it hits. Every
>spot will give the same rebound.  But for the energy the bat adds, the ball
>needs to hit at the spot where the greatest force from the bat will
>transfer. There is only a limited amount of energy, and if some goes into
>your hands (the reaction force), that takes away from what is available to
>the ball. The center of percussion is the spot where all of the energy of
>the rotating mass is focused.
>
>In our situation the strings are not speeding towards the hammer assembly. A
>better baseball analogy for us might be T Ball: the ball is stationary and
>the bat is the only thing in motion. Does that help you see why the center
>of percussion is the best place to hit it?

Not yet.  It's unclear in this analogy, to my mind, whether the 
hammer is playing the role of bat or ball.  The thing I wonder is 
whether moving the CP to the hammer will cause more energy to be 
transferred to the string, as you say, or cause the hammer to rebound 
more vigorously, which would seem to result in less energy being 
transferred to the string.

>
>I've appreciated your observations and questions. They motivated me to do a
>little more research. It would be interesting to do some testing by adding a
>little mass past the hammer to try to bring the CP right to the hammer.

I agree.  In the bass this probably wouldn't cause a problem.  In the 
treble we might create a problem by creating a very heavy strike 
weight.  I suppose it would be an easy calculation to figure out the 
increase in SW at the top to bring the CP to the hammer.  Maybe I'll 
do that later.

>  My
>calculations in the other post used the 11 gm bass hammer, which gave a cp
>pretty close to the hammer. Obviously, in the light treble hammers the
>Moment of Inertia of the shank assy will play a more significant role, which
>will move the CP closer to the pivot.
>
>Bill Spurlock recommends in his hammer hanging pamphlet to thin the treble
>shanks to remove mass, saying that will eliminate some of the "woody" sound
>that the you get in the extreme treble. I wonder if the woody sound is a
>result of the cp moving away from the hammer closer to the pivot. The
>resulting higher reaction force could be vibrating the shank assembly
>generating the noise. Thinning the shanks would move the cp back closer to
>the hammer.

An interesting observation.  Could be.

>
>Somebody needs to do some experimenting with adding weight past the hammer.
>
>I realize now the number I came up with for the cp is the same as the answer
>you got, but I was confused (I get that way easily) as you didn't tell us
>anything about how to get the moment of inertia.

I didn't want to bore everyone.  I figured those few people who were 
interested in doing the math could do it themselves if they wanted to 
check my figures.

Phil Ford

>  So I incorrectly assumed
>you didn't use it. Mea culpa.
>
>Blessings,
>
>Dean