Hammer Shank Ratio

[Richard Brekne]

Phillip Ford wrote:

> The point that I was trying to make is that if you are talking about a weight, or force, balance then it probably makes sense to talk about the points where forces are applied:  The hammer/shank CG and the knuckle contact point.  If you are talking about movement, or distances, then it probably makes more sense to talk about the points where you care about the movement: the hammer strike point and the knuckle contact point.  These are different sets of points so the 'ratios' that you derive in the two cases
> will be different.  Just because something is a lever doesn't mean that the leverage ratio is going to be the same at every point along the lever. You pick different points on the lever and you get different numbers.

I think it goes without saying that if you measure different points you will get different arm lengths and essentially a different lever. I have made that exact point several times now. But changing the force vector alone at either the input or output point will not alter the levers leverage. It just will change the net force either applied to the lever, or to the thing being leveraged. A force vector is a seperate, independent component.

Of course if you want to look at any one of an infinite amount of discrete points through the key stroke, you will find a different effective leverage for the entire system for each point. . But we dont do that.., and if we were to... then it applies just as much for distance and speed relationships as it does weight. Just as we are interested in how much total movement at the hammer results from the amount of key movement through the key stroke, we are interested in how much weight, and how much speed.

The point is that the factors that influence the effective ratio of the system are the exact same for both speed, weight, and distance anyway you look at it. This is true for any given discrete point through the keystroke, and it is true for the keystroke seen as a whole.  So if we are going to get all hung up in analysing force vectors at this or that point, then we need to do that for all three perspectives. And none of that is necessary.

What is needed is a common language for describing the overall action ratio... "overall" meaning the net effect of all discrete points. We seem to have no trouble conceptualizing this if its distance we are talking about... but in reality its exactly the same thing for distance, as it is for speed, as it is for weight.

So it just remains to find a convention of measureing the distances of the arms of the levers that corresponds to this  SW ratio.

Let me turn this all around a sec....Using the formula Ron Overs gives. I could calculate the amount of weight needed at the key to balance 10 grams placed on the tip of the hammer. Now of course I could choose to do that for any given point through the keystroke, and of course that would vary... but the overall action ratio is not just any one of these points... it is the net effect of all of them.


Now on to a point of order.. more or less removed from the discussion above.

>
> The position of the jack relative to the hammer shank has no bearing on the direction of the force being applied at the jack contact point, just as the angle of the hammer head and hammer shank have no bearing on the direction of travel of the hammer strike point.

It certainly does. It is in the end the jack that exerts force on the knuckle, and the angle formed between the jack top and the hammer shank line is the critical one. That the jack remains stable for most of the key stroke relative to the whippen center line (and is perpendicular to that line)  allows you to disregard the jack and look only at the whippen center line... because that means the jack top is on that line. But this changes the minute you hit the jack tender, or better said.. the second you change the angle of the jack relative to the whippen center line.



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