> One could, in principle, make a plastic jack _exactly_ like, in mass and dimension,
> a wood one, which fitted with raven and boar would be indistinguishable
> from the "real thing."
... but if you for example tap the side of a plastic jack it's going
to make a plastic-y noise - I don't think any amount of engineering
can make plastic mechanical parts *sound* like wood in a situation
where they may be continually making glancing collisions. At least
from what I've read that is the operative difference.
In the piano world (Kawai plastic parts) it is a little different
since the action should be silent in any case - the debate seems to be
over the role of various mechanical properties, eg flexibility.