Making a Wooden Globe, page 4 of 4
by Marco Aurelio R. Guimaraes
marcoarg@terra.com.br
With the globe set done, it was necessary to support the wood ring horizontally. The four columns were turned on a wood lathe on which I made some modifications in order to improve its performance turning marble. After trying a few unsuccessful approaches, turning marble the way we turn wood appeared to be impossible.
Since the marble I used has several white veins of Calcium Carbonate (Calcite) with different hardness, the result is an oval or cracked piece, or worse, a Greek ruin column completely broken. The solution I found was to make a jig using galvanized pipe and a plain angle grinder that could travel along and parallel to the axis of the piece to be turned, as illustrated below.
The grinder could also be tilted up and down so that the abrasive disk could be controlled, penetrating more or less in the rotating marble piece. I fixed an aluminum bar in the handle housing of the grinder so that the disk could not abrade beyond the right point, by touching a horizontal piece of scrap wood (not shown) that worked as a guide whose shape was identical to the column curve. Since this guide limited the tilting movement, it was easy to maintain the exact shape in all four pieces.
In the library of the Architectural University of my town, I could study the several types of Greek columns. I decided on the Corinthian style whose capital in my opinion is more decorative and detailed than others such as Ionic or Doric.
The Corinthian capitals of the columns were cast in silver according to a model I pre-carved in a special kind of wax (jeweler's carving wax). The bearings, figures and the marks indicating the degrees on the wooden ring, feet, etc. were made in the same way.
By the way, the eight golden feet do not really support the weigh of the entire work (which weighs about 70 pounds). The mass of the whole set is actually supported by a retracted orthogonal base of marble on whose underside was glued a strip of leather. Without affecting the appearance of the set, the metal feet were suspended 1/64 " over the plane of the lower surface in order not to scratch the supporting furniture.
For the columns and the base, I used a Spanish marble, commercially called Emperor Brown here in Brazil. For the mariner's compass, I used different kind of marble and granite in contrasting colors. In its center I inserted a magnetic needle, commercially available, which is the only piece not custom made in the whole work.
The methods for working with the marble and metal components are not fully described in this text since the focus here is woodworking. However, all tools and machines I used are regular, ordinary stuff that may be found in a typical amateur workshop such as mine.
The wood parts received a finish of several layers of an Italian spread polyurethane varnish dried in a painting stove cabin.
A special kind of UVA and UVB ray protectors were also used so that the contrasting wood colors won't easily fade or quickly lose their original nuances.
Finally, to enhance the decorative effect of the piece, I set a diamond stone in the location of the capital of each country. In order to solidly fix the gems in the wood, I used the "English Gem Setting" process that consists of embedding the diamonds in the rim of small silver tubes called "canovon " (about 5/8 " long), which were glued with two-part epoxy in appropriate pre-drilled holes in the wooden globe. That way it would be possible to avoid future problems due to the inevitable expansion and contraction of the wood that might loosen the gem stones from their respective locations.
I have to say that my wife loved the gift, which is now in the living room of our house. Sometimes she uses it to teach Geography to our small grandchildren, so I feel myself happy in knowing that my work could be appreciated not only as a decorative piece but as a useful instructional object as well!
LAST NOTE
Since I am not a professional, my only interest is to share my amateur experience with other woodworkers, hoping that some of the techniques described here may be helpful for their own projects.
Marco can be reached via email at
marcoarg@terra.com.br
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