I've not built one, but i've seen a few in action. The mechanics are very simple, especially if you plan to use a tool the same size as the primary.
(and I'm sure you have googled the designs by now)
What they don't do, but my mirror making mentor David Sinden
http://www.britastro.org/iandi/mariot04.htm did: Rather than clamp his mirrors in position he attached a threaded plate to the back with pitch. It was very neat, and the 'nut' screwed onto the lower spindle when on the bottom, and captured a peg coming down from the upper arms when on top. I'll draw a diagram!