In a previous thread on Precision Tools in Woodworking (which got way too long and tangled), the subject of ancient methods of creating a straightedge was mentioned. A fascinating discussion also popped up about how making an accurate straightedge, or even a very flat surface, required not two but three pieces. Here is the ancient way precision straightedges were made, using just two pieces of wood, as I was taught it in Japan. Thoughts and comments are appreciated.
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In Japan they call this tool an “awasej jougi” with “awase” meaning to “join together,” and “jougi” meaning “straightedge”. I made this one for fettling the soles of wooden-bodied planes. Unlike a steel rule, it will not dull or chip a plane’s blade. For obvious reasons, it is useful to notch the reference edge where it would meet a plane’s blade, but I have not done that to this one.
I don’t know where this type of tool originated, but I don’t pretend it was Japan. The ones I have seen in the West were joined with two dowels. Mine is joined with two dovetail pins made of a Japanese variety of closed-grained oak called shiragashi (quercus myrsinifolia). And because hinoki is a bit soft, I have glued bamboo wear strips to its edges. This tool is 26 or 27 years old and has seen a lot of use. The wood is unfinished hinoki. If you decide to make one, I do not recommend using the oaks commonly available in the US for the body: too unstable IMO.
Hinoki, aka Japanese Cypress, is a most excellent wood highly prized in Japan. While not germane, it is interesting to note that scientific investigations have revealed that Hinoki develops its maximum strength around 300 years after the tree is felled. This characteristic is thought to be a major factor in the number of truly old shrines and temples remaining in Japan. Hinoki is pure joy to work with handtools, more than any other wood I know.
Another interesting thing about this piece of wood is that it was once a part of one of the 125 buildings that comprise Ise Shrine in Mie Prefecture in Japan.
http://www.isejingu.or.jp/english/ http://en.wikipedia.org/wiki/Ise_Grand_Shrine
As you may know, some of these buildings are rebuilt every 20 years consistent with Shinto principles of death/renewal. The wood remaining from the dissassembled buildings is called Shingi, （神木）or God’s Wood, and is eagerly sought by the devoted at high prices. I didn’t pay anything for it, though. Here’s the story.
When I was a much younger man with a full head of hair and faith in humankind, I was in a town called Ise Shima near the Grand Ise Shrine. The plan was to see the Shrine (or at least those parts they let the public see) the next morning, but a typhoon passed through during the night. One of the giant trees surrounding the grounds was toppled by the high winds smashing a building to pieces. By the time I arrived early the next morning, the Shrine was closed, and workmen where already busy with chainsaws cutting the boles of trees fallen across the path into segments for removal. Others were cleaning up the debris of the destroyed building. Of course, most of this debris was pieces of shattered hinoki wood, a significant amount of which had been flung outside the grounds by the violent impact and the high winds. While everyone was gawking at the damage, I begged a workman for a piece of the shattered wood from his garbage pile and, with his permission, I wandered off with the biggest piece I could handle and hope to carry back home on the train.
Some people warned me that wood obtained from such a tragedy could only bring bad luck. Later, others accused me of impious behavior for turning God’s Wood into tools and jigs. But I think the wood deserved better than to end its existence in a garbage incinerator in the ignoble company of old newspapers and dried potato peelings. In any case, because of the source of the wood, as well as for sentimental reasons, I tend to treat this tool with unusual respect.
The two dovetail pins ensure the halves lock up very tight. To make the edges straight, the halves are joined, and the edges are shot using a well-tuned plane with the blade at a very fine setting. Because this tool is short at only 400mm long, a dai naoshi plane works well with this hard variety of bamboo. Separating the halves and placing the two edges together reveals major deviations from straight/flat by effectively doubling the error. Finer corrections readily produce a very straight/flat edge. I have never precisely measured the degree of straight/flat this tool is cable of achieving, but it is good enough to tune the sole of a plane. Looking at it last night, it appeared to be few thousandths out of tolerance, probably a result of the bamboo. Perhaps if I had made the tool with the off-edge cut to a curve like Christopher Schwarz recommended recently it would be more stable. It would certainly be more attractive. It's a very utitilitarian, no-nonsense, design.
My tool has one fault that would be easy to correct, but which I have neglected to undertake for sentimental reasons: The bamboo wear strips are too wide and do not let light pass as easily as narrower edges would. If you decide to make one, I suggest you use very stable wood, and saw the two halves from the same piece of wood and located immediately adjacent to each other.
While it would serve, I don’t use this tool as winding sticks. I use two framing squares instead.
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Originally Posted by Stanley Covington
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