Pointing machine

Quoted text begins.What is this "Rovai's description" you are talking about
End of quote.

Hey, Norman

Rovai describes a number of traditional ways of indirect carving - mapping out
points on the surface of a rock. Each method depends on taking 3 points on a
reference plane, then measuring relative to these points. Simple to do.
Difficult to describe in a book with illustrations. Frustrating to descibe over
a text service!

The simplest version (pp138-140) describes laying a horizontal grid over a
bas-relief original and measuring vertically from this plane. Final finishing is
done 'by eye' after the points are mapped.

Slightly more complex, but using the same principle is the pointing machine -
also known as a 'Skopas' after the famous Greek sculptor - made up from the
'cross' and the 'machinetta'. There is a good illustration on p144. The cross is
made from two pieces of timber nailed together like a reversed 'T' with spikes
projecting from its extremities. The spikes reference original points on the
model, corresponding to similar points on the workpiece.

Attached to the cross is the machinetta, which is a movable contraption made
from clamps and swivels, used to reference a fourth point to the first three
points set by the cross.

Another method of transferring measurement is by using the callipers. Same as
before, three points are set on the original and transcribed to the workpiece.
Rovai describes how he blackens the surface of the work with charcoal and water
(p63) so that white scribed marks show up in contrast. A fourth point is
transcribed from the three set points - that is, three arcs are scratched on the
stone surface above the desired point, and the stone gradually removed until the
arcs almost intersect (p164).

The advantage of using the callipers is that scaling can take place as the
measurements are transferred. I don't think there would be a need for an
assistant on a smaller piece, as only one measurment is transferred at a time.
Perhaps you would need a hand with holding a large set of callipers.

The other method of mapping points is by the direct method, that is, sculpting
by eye, without using a skopas (p178)

The book is available here:
http://www.pietrasantart.com/Rovai/BookIT.htm

Regards,
Simon