for you pros.....

["John VanCamp" <jvcstnwrks@zzzzzzzzzzzzz>]

Robin... Most any banker made of heavy timber will support this
kind of weight.  My work tables are mostly built of doubled
2x4's for legs (4x4 nominal) boxed framed at the top and about
2/3's the way down with 2x4's, x braced on all four sides and
capped with 3/4 inch plywood.  Have been known to work pieces
weighing in excess of 2000lbs on this type of table with no
concern of collapsing.   I feel from your inquiry, you are more
concerned with the piece remaining upright while you are
hammering on it.  This is a legitiment concern. and one that I
have had to deal with several times.  Most recently working a
piece of leuders ls that was roughly 16 inches x 28 inches x 6.5
feet long into a vertical abstract.   Since a piece of this
nature will most likely be pinned to a base, My solution has
been to pin the rough block to either what will become the base,
or a scrap block large enough to pin the working piece to.  The
entire rig can be blocked up to a comfortable working height by
any of several methods of cribbing  (simon and bob have
mentioned a few).  Problem with a tall piece is that when one
area is at a comfortable height, other areas are not.  There are
hydrolic lift tables that can help one work around this, but
they are heavy , and awkward to move, so my solution is to
position the stone, and then move to it rather than keep moving
the stone to me.  The above mentioned piece was placed on a base
 from the same stone ledge, so the bottom of my sculpture was
about 16 inches off of the ground. and I was down on my knees or
sitting on the ground when working the lower part. while the top
was over 7 feet off of the ground, and I was working on
scaffolding.  There are times as an architectural carver that I
have had to work stone already set in the wall, and that often
presents some difficulties in positioning oneself to the stone,
but a way can always be figured out.
Good luck
John VanCamp / JVC Stoneworks