More off the wall stuff

[Richard Brekne]

Hi Ron.

My problem with the method you give below Ron is that it doesnt correspond to the
hammer shank ratio taken by weight measurements... and it should.

There is more then one way of measuring the ratio of a lever to be sure, but
regardless of the method the result simply has to be the same... or you have an
arguement with Archimedes and his law of levers. I dont find that measureing down
to the knuckle/jack contact and up to the hammer center top both from the flange
center pin does that.

The weight measurement of R and whatever results from measuring the distance
between fulcrum, force, and lifting points has to be the same because d1 * W1 =
d2 * W2.

I find that measureing along the shank yeilds the same result on average as the
Stanwood method of finding ratio yeilds. Both as the hammer shank ratio isolated
from the rest of the action, and as a part of the whole. This lack of consistancy
with the weight ratio, along with the differeing ratios for bass and treble
hammers, leads me to believe that it is better to measure along the shank...ie
centerpin to hammer moulding center / centerpin to knuckle core center.

Cheers!

RicB


Overs Pianos wrote:

> By the way Richard, a couple of weeks ago when I wasn't paying
> attention, you mentioned some difficulties you were having using the
> hammer/key ratio formula we use. Your comment about the bass hammers
> verses the treble hammers is correct however. The ratio for the bass
> hammers will be a little higher than the treble sections (all other
> things being equal), since the greater boring distance of the bass
> hammers will result in a longer diagonal length from the hammer
> centre to the hammer strike point. However, you will find that most
> modern action installations in which the hammer core is set 130 mm
> from the centre pin will typically have between 138 to 140 to the
> striking point of the treble hammers. I tend to use this a standard
> when calculating the hammer/key ratio. You mentioned in your post
> about the hammer shank ratio being around 7.6:1 if you are measuring
> a 130 mm shank with a 17 mm roller slot. However, the important two
> hammer lever measurements will be the diagonal length from the hammer
> centre to the hammer strike point and the diagonal length to the
> roller jack contact point. If you look at these figures you will get
> typically around 138 to the strike point, and around 20 to 22 mm to
> the roller contact point. This will result in a ratio for these two
> length of around 7.0. At the end of this process, no matter which way
> you measure the ratio, we are all primarily interested in how many mm
> the hammer strike point moves for each mm of key dip. An examination
> of blow distance and dip alone will tell us nothing, since the let
> off and after touch consumes key dip for its execution.
>
> Ron O.
> --

--
Richard Brekne
RPT, N.P.T.F.
UiB, Bergen, Norway
mailto:rbrekne@broadpark.no
http://home.broadpark.no/~rbrekne/ricmain.html