Seamless Cuts (Four of Five)
13 March 2008
One of the hardest things to do in woodworking is to join two pieces of wood together without a glue line. The glue line is just that, a line of glue made visible because of a gap between the two pieces of wood. It’s because saw cuts often produce tiny ridges that tend to keep joined wood open just a hair, a hairline crack that often is not visible when the piece is dry-fitted.
Just edge-jointing two pieces of wood can be a long dance with glue lines until one either learns how to use a sharp wood plane or gets a saw blade capable of cutting wood smoothly enough to eliminate the ridges that may not have been visible while the wood was dry-fitted, but that jump out as soon as varnish is applied to the finished product. So imagine, if you will, the problems associated with joining together thousands of tiny bits of wood into a single seamless whole. And it has to be done, because not doing so produces an outline around each and every piece of wood used in the marquetry, a glue line.
The saw blades used in marquetry are very sharp and very fine—often not much more than a thin wire with saw teeth!—so the problem is not ridges formed by a ragged cut, but rather, the gap between pieces of wood. Part “A” must butt to part “B” exactly. If either part is cut too large or too small, however slight that difference in size may be, the result will be a glue line. And simply stacking up veneer and cutting everything at once isn’t going to “cut it” (sorry!) because unless proper methods are used, there will be a gap produced by the saw kerf, which is the gap produced by any saw going through wood, because where the saw was has been turned to sawdust.
To solve this problem devotees of this type of marquetry routinely draw their designs with lines that are about a tenth of a millimeter wide. The design is subsequently transferred to the veneers they will use in their finished designs, and they then use a method whereby they saw away the “outside” half of the line for all the “inside” pieces of the design and saw away the “inside” half of the line for all the “outside” pieces, those used in the background of the piece.
The virtue of this method is that it completely eliminates the saw kerf (and the glue line), but in order to work, it is absolutely essential that the saw blade cuts absolutely straight up and down. And not just an occasional cut. Every cut. All day long. So, how the heck are we going to do that?
NEXT: “The Marquetry Donkey” PREVIOUS: “A Thousand Parts”
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