The dowel hole placement was a bit of trial and error. I looked at various YouTube but the explanations weren't totally clear to me. I cut an extra piece of the ash and the walnut so I could experiment with the placement. I found the hole needed to be in line with the start of the 45 degree angle, centered on the piece. If it was too far up, the pivot action wasn't possible.
I do my keyhole slots on a small table top router setup so I'm using a fence. The only way to do that is horizontal. I guess handheld with a jig would be an option for vertical. I've always used my router table with fence so was just VERY careful to mark the start and stop so I didn't cut outside the stationary walnut pieces.
To prevent the movable pieces from falling, I clamped everything tightly from the ends so there would be a friction fit (or at least as much as possible with the alignment issues) when I glued the stationary pieces to my backer board. Plus my dowel fit relatively well (not too loose). This seemed to work so they stay upright until needed. I saw one video where the person used small magnets so I guess that would be an option if the pieces are too loose or for added security.
