Thursday, September 17, 2009

First Light XLVII

This is the 47th post in a build thread about a Japanese freestanding garden lantern of my own design - previous post installments are linked in the 'Blog Archive' to the right of the page, so visitors new to this blog may wish to look there before proceeding - if so, you'll need to set aside a little reading time.

Continuing on then with the fitting of the main post to the foundation stone. When I left off yesterday, I had scribed the line, knifed it, and then completed the rough cut of the base of the post with saw and chisel. The next step was to trim right to my line using a bench chisel with a convex bottom, or o-ire soto maru nomi (追入外丸鑿) as it is referred to in Japanese:

I carefully worked around the knifed line along the perimeter of the post with the chisel.

Now, the stone is convex and the underside of the post must be hollowed to fit it. In the past I would gouge out the post bottom with a chisel, however the resulting surface wasn't especially clean as I don't actually have the ideal curved gouge for that task. These days in fact I prefer a more expeditious solution: my Metabo 4.5" angle grinder with a 60 grit flap wheel, normally reserved for working on metal:

The aim is to hollow the post in the middle ever so slightly greater than the surface of the stone, so that the post will fit tightly along it's perimeter and not wick water into the core region. In the past I also used a circular saw to do this task, brushing sideways with the exposed blade, guard retracted- not the safest practice, with the femoral artery rather close to the action. I virtually never grind wood with abrasives, however this task is one exception.

After a few seconds swabbing with the grinder, the post base looked like this:

A clear example here folks of the difference in surface finish between rough grinding and rough cutting. Even with using fine sanding grits though, there is still a different surface left behind whether using abrasive cloth or a blade, one scratched, the other sliced. I avoid taking to grinder to the edge of the post, as it is all too easy to go too far too fast, so I prefer to make the final fit adjustments with the refinement a chisel allows.

So, after all that, it was time for the first trial fit:

Obviously, a little material in the center is still keeping the surfaces from meeting at the perimeter. It's hard to know exactly where the high spots are by looking, so I use something to transfer the marks within the space between post and stone - carbon paper:

Carbon paper is getting hard to find at stationer's these days - this time I had a 'choice', if you can call it that, between a pack of 100 sheets or to buy a ledger book with two added carbon sheets in it. I bought the ledger book.

The paper in place, carbon-coated side up, the post is placed back in position:

The key thing with this process is to make sure the post goes back to the exact same position each time - otherwise you will find yourself going around in circles and a good fit becomes quite elusive (ask me how I know!). I've used chalk for this task in the past but I find that kind of messy and vastly prefer the results from the carbon paper method. Speaking of results here's what I found after giving the post a little to and fro rub on the stone:

So, the black-marked high spots are worked down, and then a refit is tried:

A lot better after round two. The procedure is repeated until the fit is satisfactory - here's the fit after round three:

The other side:

At this point was very close and needed only to do one more round to get a nice fit.

Stepping back a few paces, here is the look of the post now fitted to the stone:

The next step was to paint the end grain on the bottom of the post with a couple of rounds of latex paint. Between coats, I then fitted the plastic liners for the threaded rod holes:

The little mark is for orienting the oblique cut on the end of the plastic with the hole correctly - it orients to the text printed on the pvc tubing.

Well, the post fitting is another tick off the list of tasks to complete. This list is getting awfully short now:

Another coat of paint on that puppy and the post is ready for installation.

Next up: the wedges for locking the post sections together. Like most of the other pegs in this lantern, the wedges are in Bloodwood. They are to be left long for the time-being:

At final install, I will trim the wedges flush with one another, slightly proud of the post face, and paint the end grain of the wedges white.

A look from up on high at the post on the stone with the locking wedges installed:

Well just one more joinery task remains on this project - that will be the subject of the next blog entry on this thread. Stay tuned.

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