Friday, June 26, 2009

First Light X

This is part 10 of a series - please look to the archive at the right sidebar to link to previous installments if you are new to this page or haven't visited in a while.

Continuing on with the work on the post cap. This is where things stood after it was fitted to the top:

The next step was to deck the top surface which had a scallop in it from the planer snipe, as I mentioned yesterday, and was far from level with the surrounding wood. I made up a couple of pieces of mdf (Medium Density Fiberboard) a material that I like for making jigs and nothing else:

With the top surface of the cap clean and flat, I then laid out the mortises for the tie rods:

As usual, as I don't don't have a hollow chisel mortiser handy, I resort to drilling and chopping to produce mortises:

Mortises complete:

Then I could check the tie rod mortises for fit:

I'll explain more about the tie rods in a future post when I have the post apart again and can show how it works.

The next step was to double-check the height relation between the top of the cap and the surrounding makitō:

Of course, I checked both diagonals too, and things were looking fine.

Then I plowed out the trench for the lowest piece in the upper tier of support beams. You might recall that I showed a picture in a previous post where the bottom of this beam cleared the top by 0.125". Well, now with the cap fitted, I realized that to plow the cap out so as to leave only 0.125" of material above the post surface would make for a weak cap. I solved this by cogging the joint and reducing the drop down of the lower beam by another 0.125", that way I believe I found a happy medium between weakening the cap too much and weakening the beam. Here's the trench:

Next step was to cut the cog seats:

As you can see, the stepped cog allows the middle of the cap to retain 0.25" of wood, giving plenty of strenght in such a hard and dense wood as Goncalo Alves, while the exit points reveal but a 0.125" step from the top of the post surface.

Following that I prepared the lower beam cog joint:

And here they are, getting to know each other for the first (uh, okay, second) time:

Was the cap done now? Not yet! Holy crow, a lot of work goes into this little cap, a piece largely hidden from view.

The hole for the electrical cable needs to pass through the cap of course. I wanted to shift the wire chase over so that it would come through the upper tier of beams away from the center lap joint, which I wanted to keep as intact as possible for strength reasons. I located a spot to the side of the upper beam, drilled a hole which came through and marked a point on the cap. From that point, I then drilled through the cap, freehand, towards the middle and taking care not to put the hole into the trench:

Then it was time to remove the cap again, using a Bessey clamp, and make a trench in the top to allow the wiring to bend to the side:

However, I was still not there yet. I needed to find a way to make the cap removable since my plan was to bevel the sides inwards. I solved that by drilling and tapping for 8 x 1.25 mm bolts. These bolts are turned into the cap, and when they bottom out on the wood below, will drive the cap up and out. Here's a shot showing the test to see if they work:

Of course, these bolts are not part of the lantern, they are simply used when I need to get the cap out during dis-assembly. When you are building something to last for the long term, you have to consider re-buildability and serviceability. I'll mark the cap so that someone in the future who is (hopefully) trying to repair the lantern will know what size bolt to use and (hopefully) will understand the intention of the holes. That's a fair bit of wishful thinking, but all I know that I sure am grateful, in any piece of equipment I work on, if it becomes evident during repair work that the maker spent a little time considering what it would be like to service their product years down the line and made the piece capable of repair. I so dislike the modern manufacturing rationale of pre-planned obsolescence.

Finally, it was time to bevel the cap. Lacking a tablesaw at the moment, I sawed the bevel waste off...

... then planed to the line, here with my 54mm Mosaku:

Lastly I pared the end grain with a paring guide and a chisel:

The finshed cap, installed in the top of the beam:

Too bad in a way that 95% of it will be covered up- the Gancalo Alves is a pleasant wood to look at, takes a nice polish, and I must say that I enjoyed the brief amount of work I did with it. Although hard and dense, it is nicely workable by hand tools, though you have to be sharp.

In the upcoming installment, post 11 in the series, I turn my attention back to the process of building this lantern ever upwards, layer by layer- the lantern housing sill, or dodai is the next item on the agenda.

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