The Meaning of Key Length

[Clark]

Hi there,

Terry wrote:

> The only thing I can identify would be that for the same 3/8" (or
> so) dip in the keystroke there would be less rotational motion in the > long key and more of an arc traveled in the short key. The increased 
> arc in the short key would perhaps cause more friction at the capstan > to wippen cushion contact point because there would be more 
> front-to-back movement in the short key compared to the long key 
> because of the increased arc traveled in the short key.

The longer key should have a smaller lateral component, and finer
resolution at the touch plate, but still at the mercy of action design
and execution, I think.

Ed wrote:

> A prime consideration is the weight of the hammers and keys.  The D 
> is a more massive system and will exhibit more inertia than the S. 
> Many think this feels better because it gives more power and control.

The "Accelerated Action" makes an interesting exercise in inertial
layout: distribution of weight is the basis for inertial calculation,
varying with the product of mass and the square of its distance from the
rotational axis. Inertia also affects flexural properties. A couple
factors influence the grain orientation in keys, I think most
substantially cost and convenience, but shearing strength is higher in
flatsawn stuff and shrinkage, for instance at key pin mortises is
minimized, all while lower in tensile strength, i.e. resistance to
flexing. Buttons and shoes certainly help in adding height (and, as Ron
Nossaman points out, they aren't made of Balsa) and so additional
strength at a critical spot. Still, it seems that crowding a bunch of
weights toward here will lessen this advantage somewhat.

Longer keys have advantage in simplifying the keyplank layout, where for
the same offset of touch and strike scales the angular offset is
smaller, lessening short grained doglegs and enabling more efficient
balance pin location. But the weight of the action assembly at least is
the same, and more often greater at the capstan (or whatever), affecting
inertia, and flex by that square of the distance from balance (anyways,
normal offsets can be compensated with proper grain selection, but check
the means required by the 75mm keyblocks in D-S keyboards).


Del Fandrich wrote a fine article on this subject a couple years ago.


Clark