I went into the Doorframe-phase of this project thinking "Well, the door's built. The frame shouldn't be too bad." Dumb. I should also mention that I've said "Well, the [blank] is built, so the [blank-blank] shouldn't be too bad" every single time I have ever built anything. But this time, I'm sure, will be different. Yes, sir. Anyway, below is a full-scale drawing of the top of the doorframe arch:
It took me a little while to figure out how the frame was going to go together; I've been thinking about the door itself (which is essentially a 2-D object) for so long, it was difficult to switch back to more three-dimensional thinking. The head-scratcher was how to make a 2" rabbet in a 7" frame? Gluing up an oversize frame and rabbeting everything with a router seemed wasteful (and potentially disastrous.) The solution (or at least as best as I could tell) was to build two frames: one that was the thickness of the door, and would fit around the door (and would serve as the interior part of the door frame), and a double-thickness frame which was slightly smaller than the door (which would be the exterior side of the frame.) Gluing the two frames together would form a rabbet for the door to shut against. But I think I am getting ahead of myself - below, the exterior threshold is being planed and detailed before glue up:
Gluing up the exterior frame. Unlike gluing the arched door, where the two halves of the arched top came together from the sides, the arch of the frame was glued up as one unit (making a kind of "hat.") Then the arch, threshold, and sides were glued together to form the frame.
Cutting out the arch with a router/trammel jig. The trick was locating the exact center of the arch in space (hence the clamped-on support beam.) The dust collector seems to be sleeping in this morning.
Cleaning up and detailing the exterior frame.
Clamping the two frames together. The temporary cross-pieces helped keep everything square and registered.