Up and down weights

[Jon Page]

At 11:48 PM 10/15/98 -0500, you wrote:
>A while back in the days of yore when the list was young, I had one of 
>those "little discussions" on the then new action metrology of DS. At the 
>time this was all in the patent process, so exact details couldn't be 
>published, and since then I haven't really followed up on the topic, so 
>I'm still commenting based on somewhat superficial knowledge derived 
>mostly herein (or is that herefrom). The gist of that discussion centred 
>around the neglect of consideration of dynamics - and I notice this has 
>come up recently in the form of the moment of inertia discussion. I do 
>understand that the purpose of DS method is not to produce a "correct" 
>methodology that considers everything, but rather one that can give 
>results better than previous methods, in the shop setting. Ok so far.

Dave would like to see all manufacturers specify a hammer weight based
on individual note/s rather than the weight of an entire sheet of felt.
For instance;      A0 = 9.7;  C4 = 7.7;  C6 = 5.7;  C8 = 3.4. 
This is hammer weight and with adding the Strike Weight of the shank
(ave. 1.8 bass) the range for SW comes to 11.5 to 5.2 placing it down
the middle of the 'medium zone'.

Heavier or lighter spec weights could be chosen.

>I would add another point here in the friction topic. There are two kinds
>of friction, static - the force that has to be overcome to allow two
>surfaces to move with respect to each other, and depends on the normal
>force between them - and dynamic, the force that has to be overcome to
>maintain a constant velocity between two surfaces in moving contact, and
>depends on the velocity of one with respect to the other. In real life we
>know it takes a heave-ho to get that freezer moving, then it is easier to
>push it with constant velocity. Static friction is greater than sliding
>friction. In the action stuff static friction is being considered, since
>the key is not moving...balance of up and down weight is just sufficient
>to get the key moving and overcome the static friction. 

When surveying an action, tap the rail lightly to overcome the static friction
and place the appropriate weight to allow a controlled, steady hammer ascent
and descent. This will tell the sliding friction, I presume; and this is
the figure to use.
A heavier weight is needed to actually get the key moving but this will
still produce
a friction factor which will show if there is a need to look further for
relieving friction.

The biggest offenders as far as friction go are key bushings/ balance rail
holes,
knuckles and hammer flange centers.  Wippen flanges as well but they do not
render great changes in friction unless they are critically stiff.


>This friction will
>be increased as DW increases (transferred through the action to the
>contact surfaces where the friction occurs) - a 10% increase in contact
>force will increase static friction between the surface by 10% - and also,
>once the action is in motion, the effective friction will be reduced, but
>it will depend on the velocity of the key. 
>Just a thought.
>Stephen
>

I can see this happening if the DW is increased by a heavier hammer
placing more weight on the lever arms. But there needs to be a significant
amount of weight for friction to be adversely affected. What_is_affected
is the DW as it related to the Strike Ratio. A hammer 1 gram heavier will
increase DW by 5 to 7 gr, depending on the leverage of the action.
This has a more dramatic effect than friction.
If lead is removed from the front of the key, DW increases, Friction stays
the same.

Just another thought.



Jon Page
Harwich Port, Cape Cod, Mass. (jpage@capecod.net)
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