Greetings EEVBees:
--My experience is in Roof Design, and the itch in my little finger is telling me that those work bench tops could sag, especially if a 50 pound instrument were left in the middle for a day or two. I think if Dave does not want his work bench tops to sag in the middle, he should install an edge frame support all the way around the top. The long runs should be 2x4 (I do not know the common metric equivalent) and the short edges should be of nominal 1x4 (please substitute OZ equivalent). The long center line should have some additional support. I recommend 1" or so square steel tubing under the top along the center longitudinal axis. It need only be supported at the ends, no attachment to the top is necessary. Doubling the end edge support (provided the doubled edge supports are screwed together up and down every 8 inches or so) with a notch (in the inside member only) to support the tube seems easiest. This arrangement would only be visible from underneath the bench, and has a relatively low (high) profile to avoid banging the knees, ouch. , but an "A" brace (not as elegant) could also be used to carry the load to the legs.
In short, as built, with point like support only at the for corners, I think you have a trampoline just waiting for the bowling ball to demonstrate General Relativity.
--I welcome any comments pro or con, from anyone who may know more about workbench design, than I do. If any one knows better, I would be more than happy to be wrong about this one.
--Also can anyone recommend a water based, low appearance factor, protectant for that raw wood. I my opinion, he is bound to need it. Hacklord's comment came in while I was writing this. More comments are still welcome.
"Measure twice. Cut once"
Norm Abram 1950 -
Best Regards
Clear Ether