Sunday, June 21, 2009

First Light VII

In the original lantern drawing I prepared, I had set up a single layer of bearing blocks, atop which the sill for the lantern housing would be placed. After some further consideration, I decided to revise this configuration. The main difference between my lantern and it's use of maki-tō and a Japanese roof on a full scale building and how maki-tō are employed there, is that in the former there is very little weight bearing down, whereas in the latter, there may be 1000 tons or more, in some cases, in aggregate roof weight. This means that in a regular building, the maki-tō are essentially pinned in place by weight. In my lantern design, this weight is simply not there - more a concern is that someone might grab the lantern top and try to twist or turn it off the post, or that it might get knocked hard from the side, which also would stress the connection between top and post quite a bit. Thus I need to come to some different joinery solutions than might be used otherwise. I have to find ways to fix things together that normally would just be compressed in place.

With the first tier of hijiki, I ended up with the 'X' assembly, oriented normal to the post face, being half lapped and relatively strong. The diagonally oriented hijiki however were disadvantageously positioned in terms of cantilever effect, and were only held by joinery such that they couldn't be withdrawn - the weak link in the assembly. I realized that if I were to put a second layer of supports atop the pillow blocks, and configure them in such a way that the diagonal pieces would be the strongest elements, then the combination of the two, first tier hijiki and second tier beams, would balance out each sets respective weakness and strength.

Here's the original configuration, and I have thus far shown assembly to virtually the same point:


A key difference is in the orientation of the maki-tō - notice that the middle ones, are rotated 90˚ differently than the maki-tō in my newer assembly (depicted in the previous posting). The other difference is that in the original version, I was to employ a special kind of maki-tō at the diagonal corners. This type of maki-tō is quite a bit more complex to make, and more importantly, when made in such a small size, is vulnerable to breakage at the little points which hang down at each corner of the block.

Here's the revised version:



In the newer version I've taken advantage of the fact that I am no longer constrained by trying to fit the assembly into the top of a post, and have thus made the two pieces of the 'X' oriented normal to the post faces quite a bit taller in section so that they can be lapped to the central pair of diagonals, which are themselves lapped. This means all the parts will have decent strength, and the central 'X' will be about 25% stronger (in material left inside the lap) than the normally oriented 'X' assembly.

A further point is that the added tier of support beams does raise the height a slight bit, but this is not big deal, and if need be could be compensated for when the post is scribed to the foundation stone.

So, on to the cuttin', beginning with the lap joint of the main diagonal 'X' assembly:


This is another half lap with mitered abutments, only 0.125" depth on the housing this time, and since I have detailed the making of this joint in past posting in this thread, I'll spare a repeat of the step-by-step photos. Here's the joint together, checking for square:


And a close up of the lap itself:


I couldn't resist a trial placement of the 'X' assembly, left long at this point, onto the pillow blocks:


A lower angle view:


Then it was time to start working on the tall-section support beams, which needed a double oblique housed lap joint at both ends and a single oblique lap at the middle:


After clearing most of the wood out, the joint looks like this:


Now, on one of them, my nokogiri hopped out of the cut as I drew the saw back, leaving this nice little scar on the top:


I wasn't thrilled. Although the scar would be concealed by the overlap of the sill piece which drops down on top of the lap, I decided to repair the slice. I found a piece of scrap and sawed out a little wedge, in the same orientation of grain as the area to be patched:


Then I tested the fit, and glued it in:


Later I cleaned it off:


Not too bad, but not a perfect match for color, though given it is completely hidden it doesn't matter - not to me anyhow.

Here I'm paring one of the lap shoulders:



And this is the completed cut-out of one of the central double oblique laps:



To be continued...on to post 8

2 comments:

  1. does it help a lot to wet the end grain of wood? is this more for mahogany? or will it work well with all woods?

    gregore'

    gregore@gregorejoailliers.com

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  2. Hi gregore',

    thanks for your question. I am not using water to wet the end grain, I am using Camellia Oil. Water is a bad idea.

    Normally I'd dip my chisel in a little pot that has a bunch of cotton wadding in it, soaked in oil, but I lost my little oil pot sometime back. Lately I have been resorting to using a spray bottle of Camellia oil -- unfortunately the plastic spray mechanism is getting worn out and is acting up, which means that half the time it doesn't spray and then suddenly it will spray a whole bunch. I was not intending to douse the end grain with oil as you can see in one of the pictures! It's better to use the little oil pot with the cotton wadding, and I'll start doing that again when I get a fresh bottle of oil.

    The oil lubricates the cut, which gives a smoother finish on the end grain, and due to the reduced friction results in a longer-lasting edge on the chisel. The oil can be used on most woods I would imagine.

    The Camellia oil is a very light oil and will evaporate pretty much entirely off in a few days. That said, I don't use the oil if I plan to bring glue near the joint later, which is not the case with this project.

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