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I hope by now you have received your August 2010 issue of Popular Woodworking Magazine. If not, purchase a copy here, or run to the nearest bookstore to indulge.
When you do open the magazine, make sure to read Toshio Odate’s article about Magobei’s Dining Table. The story behind the table is fascinating, but the meat of the article is, of course, how the table is built. The joinery is masterful , strong, well-designed, perfectly executed.
Do yourself a favor though; don’t turn to the pages if you’re short on time. It’s so easy to get lost studying the joinery that you’ll surely be late for whatever it is you have to do. I spent more than a few days examining the joinery to try to discover every aspect of the table. And I spent additional days working up the SketchUp drawings (click here to download your copy). Even after studying the project that much, I still missed a joinery detail along the way. My apologies to Toshio.
Above is a portion of the table as depicted in the model. Look closely at the intersection of the legs to the beam. The joinery, as you see it, is tremendous. For most woodworkers, twin tenons would be sufficient. But Toshio pushes beyond ordinary. The addition of the two outer, non-shouldered tenons adds to the structural integrity of the joint. If your inside tenons are not a snug fit, those non-shouldered tenons increase the rigidity of the table for front-to-back movement. 
Next, take a look at how the joint should have been shown. Toshio, interested in having the table stand for more than 300 years, fits the top portion of the leg into the bottom edge of the beam. That 1/2″ of material increases support and takes a portion of the stress off the non-shouldered tenons. With both techniques to reinforce the joint, I’m willing to bet this table will be seen and studied by woodworkers after the year 2300 , if man survives.
Looking for more on Japanese furniture? Click here for a quick article about interpreting select pieces. For a more in-depth study of Japanese joinery, you may be interested in this book, click here. Of course, you cannot achieve precision joinery without sharp chisels and accurate workmanship. Pick up a copy of David Charlesworth’s DVD on Chisel Techniques.
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I keep looking at that joint and I keep wondering whether it really will show up in 300 years.
If you cut across the beam through the area where the mortises are, you will see that perhaps as much as 80 percent of the effective cross section of the beam is gone. I just have this gut feeling that this puts a huge amount of load on the 20 percent of the beam that remains there.
I know that the tenons fill that void in quite admirably, but any stresses on the leg lateral to the beam are going to put huge stresses on the 20 percent of the long fibers remaining, particularly since the stresses are going to be amplified by the length of the leg and the extreme mass of the table top itself.
I would have made the leg with only one major tenon instead of two.