There are several methods of obtaining the smooth rotation of a piece
of metal necessary for engraving on it. Many North West Coast American
Indians use a hard leather pad and hand control to do it. One can install
various chucking devices onto a heavy base as well. A standard machined
engravers ball can cost $500 and more. This version costs less than $30.00.
In the version I came up with described here one uses plumbing parts
from the hardware store and cement to produce the weighted, swivelling
bottom unit. An aluminum tube from an extruded aluminum dealer is set
into a large pipe floor flange and this forms the top rotating part. Pitch
or dopping wax is used to fix the metal in place for engraving. Other
arrangements could easily be used. The top rotating unit slides and rotates
over the bottom unit; a standard steel pipe section threaded into a second
smaller floor flange which has bolts through its screw holes. Nuts on
both sides of the flange hold them in place. The bottom floor flange unit
is then set into a concrete hemisphere made by pouring cement into a stainless
or plastic bowl with a diameter of at least 8 inches or 20 cm. The bottom
unit is embedded into the concrete by gently twisting it into place and
hung so that it sits level and flush on the surface of the concrete until
it sets. Cement provides a smoother surface than concrete. I toss in steel
junk or tire weights for extra weight (when the cement has half filled
the molding bowl). This works as a method for obtaining pitch bowls as
well.
Several top units can be made and work very quickly exchanged by changing
top units-more quickly than with a standard engravers ball. If built correctly
the rotation is as smooth and easy as a five hundred dollar version. This
one should cost about twenty-five or so. The only tricky part is finding
the aluminum tube for the top unit. It has to be of a size that is threadable
so it screws into the top floor flange and yet has an inside diameter
such that it fits smoothly onto the standard steel pipe section jutting
up from the lower floor flange. The aluminum tube if filed down a bit
will self-thread into the iron floor flange. I have made several of these
and they work really well. When in use the concrete hemisphere is rotated
and positioned in a sand bag or a ring of leather or wood. An old leather
or canvas handbag filled with sand is great.
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