Old piano design (was Re: puzzler)

[Clark]

Hi, Stephen,

> For one thing there were no blueprints because they didn't need 
> drawings. For second thing historical thinking about angles always 
> centred on the tan (rise/run) etc. Angles were always though of in
> terms of their tangents, not degress. As for the angle of the 
> bellyrail, this was almost certainly laid out by measuring back a 
> fixed dimension at one end, e.g. one end half-inch further forward 
> than t'other [these inches being not modern English inches, but a
> builder-specific inch unit in many case].


This grand, ca.1836 I looked at in March made an interesting study. The
front of the soundboard is floated on a liner - in this case, at two
angles following a similar curve to the bridge and bentside (other
illustrated examples seem to have the same curve). Wrest plank
perpendicular to cheek and spine, parallel to the tail and its back edge
defining the strike line (!!).

Bent side sawn, results suggest two arcs tangent on the line of their
centers, 2434mm and 608mm radius - very close to 4/1 ratio. Long bridge
essentially has the same shape, which makes a good approximation to an
exponential curve minus strike lengths. The larger arc - definitely
curved - needs for a larger trammel than any flat part of the instrument
accomodates, though - length: 1651/1493mm, width: 1135mm, tail width:
521mm, cheek length: 616mm (bentside run =~ cheek length, bentside rise
= length - cheek). Would they have used marking templates by then?


Clark