I am aware that 12mm is very thin - my reason for using this thickness
is that 12mm main panel thickness + 6mm thickness for the false frame
= 18mm which is approximately the thickness of my edge frame (21mm or
1" nominal i.e. before planing). I guess I could go to 15mm thick MDF
but the stuff seems so heavy......
I think I might do it the other way round. 6mm panel and 12mm false frame.
If you want the panels recessed, screw through the 6mm into the 12mm from
the back.
IME only kitchen type concealed hinges work long term on mdf