hammer "throw" on hard blow

[David Nereson]

V T wrote:

>Hi David,
>
>When hammers are bored, it's really important to drill
>the hole so it passes right through the vertical
>center line of the moulding.  (This imaginary line is
>inside the moulding.)  The desired effect is to
>ditribute the mass of the hammer about evenly on both
>sides of the hammer shank.  I often see hammers that
>are not bored very accurately and the heavier the
>hammer, the worse the problem will be.
>
>This too is an approximate solution to the problem. 
>On bass hammers where you might have, say, 15 degrees
>of angle on the hammer relative to the shank, the
>weight on one side of the hammer will be closer to the
>action center than the weight on the other side.  That
>really isn't balanced either.  However, you can see
>that the problem could be quite serious on a heavy
>bass hammer that has been drilled off center, and in
>such a manner that the side that has its mass further
>from the action center is also further from the shank.
>
>In that case, you have an unbalanced mass that is
>about 5" away from the center pin, so that can cause
>quite a distoring force on the bushing and the shank.
>
>Hope that applies to the problem on hand.
>
>Vladan
>
>  
>
 Yes -- I hadn't considered the hammer being bored off-center.  I kept 
checking the hammer-to-string mating, and it seemed OK -- i.e., when 
held against strings by pushing on the butt (not the hammer tail), then 
plucking the strings, none of them "ring" longer than the others.  I 
encounter these "shaking", or wobbling hammers a lot on the Hamilton 
studios, and some Yamaha studios and uprights, especially in the very 
low tenor, where they have a few shanks longer than the rest of the 
tenor section.  But when there's a lot of them, I can't imagine they're 
all bored off-center.  If they are, it's not by much (I haven't miked 
them), but maybe it doesn't take much.
    I checked the pinning very carefully since that was the most likely 
suspect.  I purposely re-pinned the thing very tight (2 swings), and 
clamped the flange in a vise first to check for any wobble or pin 
movement.  I check the feel of the center pin in each bushing 
individually, just feeling for equal resistance when pushing the pin 
in.  The pin is definitely tight in the birdseye.  
    I'll have to check for off-center boring again.  I can see where on 
the angled hammers, more weight could end up on one side of the shank 
than the other, but when straight-bored hammers shake laterally after 
impact, that's what's puzzling. 
    Thanks for the responses.  --David Nereson, RPT