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:
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:
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:
And, the intermediate ribs mostly done, back together the roof goes:
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.