making two curved marble surfaces meet in a clear line (like OO -- something V-like)

[Don Dougan <dondougan@zzzzzzzz>]

Andrei;

When I do a pair of forms meeting like that I use one of two methods,
which one depending on the depth of the 'joint' between the two curved
surfaces.  Being self-taught as a carver, I don't know how one would
traditionally do it in a carving studio, but my methods do work.
Assuming the stone is marble or softer, I would probably use hand tools.
For harder marbles and stones I might use my 1/2" short-stroke Trow &
Holden pneumatic with the air valve turned down to a purr (just enough
pressure to prevent stalling the hammer).

For relatively shallow intersections I use my flat chisels (high-carbon
steel ground to a fairly thin profile) and cut into the groove -
alternating from either side - in a series of strokes with the chisel
held so the cutting edge is parallel to the groove.  Each series of
strokes is used to remove a layer, with each succeeding layer creating a
sharper (more narrow) V-groove.   The chisel is held more steeply
perpendicular with each succeeding layer, and the final layer of cutting
is done with a very sharp chisel -- I prefer to use a mallet or a dummy
rather than a hammer as the striking tool to finish the cut.  The
specific angle of the chisel to the stone surface changes with each
stroke of the mallet so as to follow the curvature of the intended form.

The alternation of carving from one side and then the opposite is
important, as is the relative thinness of the layer being removed in a
particular series of strokes.  Trying to remove too great a thickness or
trying to do it only from one side doesn't work very well.

If the depth of the joint between the two curved surfaces is relatively
deep and narrow I might use a diamond saw blade to cut the groove first,
followed by chiseling in the same manner as described above.  Obviously
the size of the saw blade (and any compound curving of the two meeting
forms) will limit this method.  After the general shapes are cut I do end
up with a narrow U-shaped groove at the very bottom of the intersection.

To resolve this into a sharp V-groove I usually drag the corner of the
sharp flat chisel through the groove and scrape the U into a V, using as
many strokes as it takes.

To drag, I position myself at one end of the intended groove, and hold
the chisel with both hands while drawing it towards myself.  The normal
cutting edge of the chisel is at about a 30-degree angle from the bottom
of the groove, with the striking head angled towards my face, leaving one
of the narrow sides of the cutting edge of the chisel in the groove and
being drawn towards me.

The scraping cut is very similar to using a scoring tool or plastic draw
knife (NOT a woodworker's drawknife) to score a grooved-line in a piece
of acrylic sheeting prior to snapping the plastic along the line, or (if
you are more familiar with etching techniques in printmaking) like using
the draw tool to cut a zinc or copper printing plate.

After the intersection is scraped to shape I might use a long thin-bladed
knife (like a cheap stainless-steel kitchen knife with a somewhat
flexible blade) to clean the sides of the narrow V-canyon.  This is
accomplished by using a shallow slicing motion to 'shave' off the surface
of the marble or limestone I might be working.  Note: it is a slooowwww
process, but allows more control than with abrasive paper or wheels.

I would be interested in hearing about any other methods anybody might
use . . .

Good carving to you,
Don
http://www.dondougan.com