After the post for the lantern was near-complete, my attention turned to the first tier of support arms which would eventually carry the lamp housing. There are innumerable variations on how these can be done:
- simple support arms, a diagonally-oriented 'X' going to the corners of the lamp housing
-simple support arms to the corners, 'X'-form, with spandrels underneath
-a double 'X', giving support to 4 corners and 4 mid-span points
-double 'X' with pillow blocks
While the spandrels make a lot of sense and also offer plenty of room for artistic expression, I designed my prototype lantern with the double 'X' supports, termed hijiki (肘木) by the way, and with pillow blocks, or maki-tō (巻斗), as I liked the look, which is a bit reminiscent of unfolded arms bearing a flower head (a lotus blossom perhaps) in each palm. Well, to my eye at least.
Now, fitting a double 'X' together in the same plane is a tricky joinery issue, especially given that it had to attach to the limited surface area atop a post and bear some amount of weight. It's not so much the loading from the weight of the parts above (negligible really) or snow, wind etc, that I was worried about - I wanted the top to be sufficiently rigid and well-attached to the post that there would be little to no give if some crazy person were to grab the lamp housing and try and twist it side to side. So the question of how to lock the whole assembly down to the post, along with giving access for the electrical cable, gave me pause for thought for more than a few hours. The hijiki need to be thick enough to resist any imposed loads, and wide enough to support the maki-tō, and allow the cable to come through the middle, but if they were too thick they would be to crowded for the available space atop the post. I also wanted the hijiki to help lock the post together, as the nearest internal dovetail locking key was about 8 or 9 inches below the top. The solution to that is that the 'X' brace oriented normal to the post faces would have a cogged lap.
This processing job entails cutting down into the end grain of the post, and there is no better tool, in my opinion, for cutting end grain than a router. First step was to establish the initial 'X', which is normal to the post faces:
Then I dropped the depth of one of the trenches by 0.25":
You can see in the above photo a pair of square mortises now cut into the post - these are part of the sneaky little plan I have devised to lock the lamp case to the post (more on that later).
Next I processed the cuts for the 'X' that is 45˚ rotated from the first, and got out the chisel to chop and pare the lap housings on the faces of the post:
As you can see, the diagonal trenches have no cog housings, the hijiki will simply lay flat in those places:
With the post top pretty much ready to go, I began work on the getting the stock for the hijiki. My oh-so sweet Hitachi monster re-saw band saw is currently on the other side of the continent, so say hello, 10" cant of Mahogany, to Mr. Miyano, one of my larger ryoba:
That ripping took a little while, and in the end I had some smaller bits to work with:
Those pieces will serve in a number of places on this project, but for the hijiki I needed to do a little more ripping on my custom plastic workstands (they're called 'systainers'):
The mahogany liked to bind the blade a little as I was cutting, so I tapped in a few wedges to discourage that:
Sawing for Teens, the new hit game show:
Next time I'll show how the joints were cut for the hijiki and their fitment to the post top.