[pianotech] Grand Backcheck Geometry

[Ron Nossaman]

> So that sounds like the specifications are empirical not something
> you can easily predict on paper.

Actually, it seems to be pretty dependably predictable unless you change 
something radically.


>So that brings up the second
> question:
>
> The 72degcheck face


(how'd you do that degree sign)

Like this °. <G> It's alt 248 on this list, and won't work at all on the 
new, devolved "system".


, 2-1/2"-3" rad
> tail, back check head height 1mm below tail at letoff, 1" min
> tail...are these specs that work on "standard" 17"-19" length
> keysonly  (call it 8-1/2"-9-1/2" back lever)?  What about a shorter
> back lever, with its smaller radius at the backcheck? ALthough "D's"
> go the other way and have longer  key lengths than 17-19, so maybe
> that shouldn't change things that much?

While there are an infinite number of things I haven't actually tried, I 
don't see how it will make any difference. It's still not a matter of 
intersecting arcs. By the time checking occurs, the key had 
theoretically (yea, I know, but resist it) quit moving. A long key that 
has quit moving is very similar to a short key that has quit moving in 
that the back check is positioned where it belongs (if adjusted within 
the already established criteria) in relation to the hammer assembly 
when the hammer tail hits it. It doesn't matter where it's been or how 
it got there. Where it's at at the point of check is where it's at.
Ron N