The izutsu-tsunagi pattern is an abstraction of the Japanese well curb, the parallel crossed supporting structure around a well. This pattern seemed like the next logical pattern to learn after asanoha. In fact, its a good bit easier and faster than asanoha. Today is the last day I’ll be spending at my Grandfathers house-sitting, so I didn’t want to put this pattern in a frame for lack of time.
I made a small square jigumi from 5/16″ kumiko using a pair of dividers to create the even interval between pieces.
The smaller squares that form the pattern within the jigumi were thinner 1/4″ kumiko material. It would be a real pain in the butt to try to make the lap cuts with the kumiko already cut to length for each square. With four pieces stacked together I marked four groups, one for each square, and cut the lap joinery before sawing them to length.
With the small squares glued together all that’s left is the diagonal locking pieces. There’s a bit of a challenge in getting each opposing key to be equal lengths. I suppose you could use a stop on your 45 degree trimming jig and slowly bring two pieces in to length through trial and error. In essence, some fitting is necessary, but a bit of math gets you closer from the start.
The small izutsu square was sized such that it formed three even intervals within the internal space of the square jigumi. So, knowing the interval between the izutsu kumiko, its a simple matter to calculate the length of the diagonal locking piece. Pythagorean theorem anyone? With a simple right triangle you can just multiply the length of one side by 1.414 to get the hypotenuse, but its useful to know both methods of calculating. I’m working to the thousandth of an inch and that is the tolerance that you need to be working with (for us poor Americans not accustomed to the metric system). I should think that if the thickness of my kumiko wasn’t consistent I would have a lot more time fitting these pieces. I’m pretty happy if my kumiko holds tolerances +-.002″ from what I want. Don’t force the first set of opposing diagonal pieces. If the fit is too tight there it will squish the izutsu square and make more trimming necessary for the remaining diagonals.
This pattern is great and I’m eager to use it in a larger shoji project, possibly as a border. Or, if I get the gumption, a whole shoji panel set with square jigumi with izutsu-tsunagi!