Thursday, June 25, 2009

First Light IX

This is the ninth part in a thread of posts describing the construction of a freestanding Japanese garden lantern. In previous posts I have described the construction of the central post, the initial tier of support arms, or hijiki, and then went on to show the construction and fitting of the second tier of support beams.

Today I will continue on with the build-up, though later on in fact it will seem like a bit of a strip down as I need to take some of the lantern apart to work on some details I had omitted earlier to tackle.

First though, the second tier of arms had been fitted together at a central 4-way lap joint, half-lap for the diagonal pieces, and 1/4 lap for the other two, which are oriented normal to the post faces. The lower piece then had to be re-shaped so it would fit on the pillow blocks. This necessitated removing about 0.5" from each end. I proceeded by ripping the pieces with the ryoba nokogiri:


After cross-cutting, I pared the surfaces down to dimension:


Then I started working the returns into a serpentine shape:


Continuing to shape the lower surface, this work done entirely by chisel:


The finished result:


There's a little more to be done yet on this lower beam, but I moved on to work the noses on the uppermost beam, on which I trimmed a slope:


At this point, with the cluster of beams assembled atop the hijiki, the scene looked like this:


You can see that the lower beam comes within an 1/8" of the top of the post. You might wonder why I didn't run it all the way down to the surface (?) - well, I have some plans for this, which I will explain shortly.

I had noticed that with the second tier of beams in place there were a few discrepancies in fit, and decided to to some checking and adjusting to the lower layer:


A couple of small adjustments were made - one of the hijiki wasn't quite sitting fully down in its trench.

Now that I had all the upper tier parts removed, I could return to dealing with a few tasks needed to be done in the lower layer. One of those concerned the routing of the electrical cord, which was to come up the center of the post. Though I hadn't cut the passage in the center of the post yet, I could now make the entry through the middle of the hijiki:



The completed hole:


Given that this is a prototype, I have made a design revision or two as the build has progressed. Another such revision concerned the connection at the top of the post. I originally designed the lantern to have a single row of hijiki and then the makitō (pillow blocks) as support for the lantern housing. Part and parcel of this design was that the central space atop the post and up to the floor of the lantern housing would be largely occupied by a hopper, as you can see in yellow in this early drawing:


With the revision in design to a two-tier support system, the lower beam of the upper tier now intersected the space in which the hopper would have been situated. I wanted the top of the post, where there was some end grain and a large number of component intersections to be protected from the elements. Wind could blow rain into that space, where it could wick its way in-between the pieces. With the hopper no longer a factor, I came up with a solution that not only protected the top of the post, but helped support the beam work and improved the strength of the entire post-hijiki connection. This solution was in the form of a cap which would be attached to the post top with a square tongue and groove joint.

First I needed a piece of material for the cap. I love the workability of the mahogany, but it didn't strike me as being tough enough for this particular role. I remembered that I had a couple of offcuts of a wood that would be perfect however: Goncalo Alves (astronium fraxinifolium). A had bought a couple of huge wide planks of it from a dealer in North Carolina several months back, a couple of planks that the dealer had imported 15 years ago and set aside for his personal stock and from which he had intended to make a dining table. That plan changed, and I was in the right place at the right time, as they say. After they arrived, I had them planed at the window and door shop just down the road. Their planer was in poor condition at the time, so the planing had resulted in some severe snipe at the ends of each board, necessitating that I trim about 4~5" off each end. That was a bummer, but for this project a blessing as I still had the offcuts:


The lighter colored sections of the piece are very close to the mahogany in color. The black streaks are clearly what set it apart, plus the fact that Goncalo Alves is about twice as dense as mahogany (the planks I have weigh about 100 lbs (45kg.) each!). It is described in one of my wood identification books as "noted for its durability", and is a wood commonly used for boat-building in its native area. This was a perfect choice of material for the cap I thought.

I made up a jig of mdf and proceeded to cut a 0.25" groove on the post top with a router:


I cut the required piece of cap, and then used the router to cut a recess in the center so that a perimeter tongue was left:


Here it goes:




It's a tight fit, by design, and need to be tapped down into place with a hammer. Once down, it helps lock the hijiki into place - the diagonal pieces in particular are noticeably stiffer after the cap is fully down on top. Now, removing the cap requires the use of a Bessey clamp to grab it - I can't do it with my grip alone. This posed an issue as my intention was to make the profile of the cap beveled on all four sides, which would make it un-grabable, un-removable by such means - this problem I also solved, to be detailed, among other things, in the next post in this thread. See you then.

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