The three boxes on the top are shown upside down due to gravity interfering with the picture. The horizontal unit bridges across the top between the two vertical units. \\Question: How to fasten the middle unit to the two ends so that it can be taken apart to move it, then reliably reassembled?
Consider using Threaded inserts. I am using some form Rampa Tech that seem to work very well. Drill a hole slightly over 3/8", maybe 10.5 mm, screw in the insert and then you can bolt the piece together with machine screws. The advantage is that you can remove and install the bolts as often as necessary without wallowing out the holes as you would with wood screws.
I am using them on the table I have been beavering on for several months. Since it will weigh about 300 lbs. I wanted to make it possible to completely disassemble it.
it seems just easier to give the whole fabrication page on my shop made connector bolts. scroll down a bit and you'l see the brass pieces then how they are employed
I would consider combining the threaded insert with shouldered, knurled thumbscrews. And just let them be visible—with her permission of course. You’ll have visible hardware either way, so this option is to use handsome hardware and make it a feature.
Or use hex head screws, with wooden caps fitted to cover them.
I recommended. One of the "features" of the Rampa Tech ones I used is they go in and remain nice and straight. I drilled the holes and chamfered them slightly and drove the inserts home with a drill and hex shaft. I have about thirty of them in this table I am working on and being out of plumb was not a problem with any of them.
OTOH I learned the hard way you do have to be VERY careful positioning them.
I bought a fifty pack and will have a few left over. I could send you some if you want them.
Seems these connectors are called a lot of names, making it hard to search. I would like to use a connector bolt in brass if I could find it. LV has black which I can live with, which I found unnamed under knock down hardware.