Just relax Bob, it was only a suggestion. It seemed to me that the only argument for deciding copper was being afraid of weakness. When Ben asked for glass, it make me clear that he prefer a transparent material; so my point was that the block could easily be made strong enough to use plastics for the top.
Myv is right; I made a very brute simplification of the problem. My intention was to do some quick numbers to show the advantages of fin continuity. I didn’t want to spend a lot of time in more precise calculations, because I’m very confident that for the small loads involved, it’s stiff enough by a big margin.
As for the added complications in the machining stage, they are by far compensated if machining a copper top can be avoided.
Further simplifications of the model can be made when using a plastic top. The o-ring channel can be eliminated and use that silicone film sealant someone mentioned. Even more, it could be used silicone adhesive and eliminate the need of bolts. It can give the block a cleaner look and avoid hole taping. I think this is ok with the KISS concept
I’m sorry if the only added work my suggestions imply is Bob’s drawing time.