Here we are, 34th post on the construction of a Japanese garden lantern. Previous installments can be located archived in the sidebar at the right of the page.
The last stage of the process in making the roof for the lantern housing is the fabrication of the intermediate ribs atop the double roof boards. These ribs help secure the two roof boards together and, on the aesthetic side, lend a tad more monumentality to the roof (sounds a little funny to say that considering how small the roof is!). At the very least they add visual interest to the roof surface, and strengthen the roof, so that's good enough for me.
These intermediate ribs are backed on top like the one-piece barge boards, however they are not curved but rather have a step-down between the roof board planes.
To begin, I created a template of the rib out of MDF:
This template was then used to layout on the stock.
From there it was a series of cutting out using my jigsaw, and then using the template, fixed with carpet tape, directly atop each piece in turn for template routing.
Once the pieces were roughed to size, I cut sliding dovetails on the bottom, one for each of the roof boards. Thus the intermediate ribs have two dovetails each, three used per side for a total of 12 mortises altogether. These are steeply angled sliding dovetails that ramp up quickly:
Here's a view of the lower tapered sliding dovetail and mortise:
The steep taper allows the dovetail to be dropped directly down and then slide forward to lock. Determining the correct amount of taper so that the amount of distance required to lock up was not too much (or too little, since an overly short travel meant too much taper and a dovetail that wouldn't tend to lock up well) was a matter of a bit of trial and error. Here's a look at the male dovetail dropping into place:
Then it's down:
And then it slides forward to the lock position:
That process is then repeated a couple more times for each lower board:
With the lower joints fitted up, i then could repeat the process on the upper boards, first fitting the ribs individually, and then fitting them to both boards at once:
Once the ribs were fitted, it was time to profile them, meaning their backing cuts, which I roughed out on the router table:
That was followed up by some work with the spokeshave to clean up the beveled surfaces - this needing a quick set of holding blocks on my deluxe workbench, er, sawhorse:
The bevels cleaned up, I could then clean out the step down sections with a chisel:
Next, I cleaned up the sides of the ribs with my 54mm plane:
With these ribs, given the way the joinery is configured, I didn't fuss too much with the thickness dimension of the part when I planed them -they vary among themselves by about 1/32" I believe.
And, the intermediate ribs mostly done, back together the roof goes:
A view from the top:
The next step will be the mortises between the intermediate ribs and the upper exposed ridgepole. For now, I put the roof back on the lantern housing:
Tomorrow I'll fit the ridgepole and then it will be on to the grill panels (and glass) which go into the lantern housing. Stay tuned for the next installment.