The rails under the seat seem to be held on with these knock-down type screws. These still held quite well, quite a bother to remove. The lock washer under the head of the screw really gripped it tight, so it was hard to undo those screws.
One of the screws, however, was missing. That may explain why this chair was worse than the others.
Looking at the joints, it looks like the dowels were inserted, and then the individual parts were painted. There was no glue on either end of the dowel. The dowel's only function was to serve as a sort of alignment pin. All the "hold" of the joint was by the screw which went through the hole between the two dowels. The screw was an M6 machine screw (about 1/4") screwed into a metal threaded insert in the leg.
My guess is that the chair was designed to be shipped in a flat package, with final assembly by screwing it together to be done in the store or by the customer. Kind of a neat way to do it, and the single screw between the two dowels had, all things considered, held the chairs together surprisingly well.
Now reassembling, with lots of glue. The glue in my glue container had gotten a bit thick because I'd left it open too much (too much water evaporated), but for this application, that was perfect. Yellow carpenter's glue is a surprisingly good gap filler
Clamping it together. My bar clamps proved less than ideal because the back legs are at an angle. The swiveling pad on the screw end of the clamp kept tilting and slipping off the corner. So I cut some angle blocks on the bandsaw. These provide a flat surface to apply the clamp to.
A band clamp would probably have worked better. I have a band clamp, but by the time I thought of using it there was no time left to start looking for it. That's always the problem with specialty tools. When the perfect application for it arises you forget to use it or just can't find it!
Cleaning up on painted parts is not overly critical - the glue won't soak into the paint, so a wet rag is sufficient to clean off any residual glue.
Those original dowels were about 8 mm. I assume they were metric because the screws are metric. They were too loose in the holes to be much of a "joint". Also, the insides of the holes on the legs were painted! So to get a good glue surface, I decided to drill all the holes out to 3/8" (9.5 mm). I inserted a drill bit in the hole next to the one I'm drilling as a visual guide to help me hold the drill at the correct angle for the hole. I would say right angle, but that would imply 90 degrees, which these weren't.
I also added a few brad nails to the dowels between the legs. I didn't have that much faith in the single pocket hole screw that held each of these. Gluing them would have been better, but with paint on both parts, that would have been a lot of work to prepare and would have made the gap in the joint even bigger.
I finished off by mixing some paint of the right colour using some artist paints, and rubbing that in the lines around the joints. My artist paints are getting old because I haven't done any paintings in years. I may end up buying more paints just for cases like this though.
The chair is now very stiff. The catch with that is it will now rock back and forth if the floor is uneven!
This was the worst of my brother's chairs, and I was going to re-glue the other ones too, but he ended up not liking this chair being so stiff. I guess some give can be nice, so long as it doesn't fail completely.
Building kitchen chairs
Repairing a chair leg