is a double layer of 3/4 plywood / finished 1 side, good enough for a assembly and general duty workbench top ?
Tony, with your double 3/4 ply idea... I'd say you're 1/2 the way there to a reeeealy good idea: torsion box design. Torsion boxes will stay dead flat, strongly resist warping/twisting, capable to handling pretty heavy loads, and don't need to cost that much (more).
Recently picked up a metal lathe from Craigslist that weighs in at ~325 - 350 lbs... but it included no stand/bench. What to do?... I'm not a welder and have no ability to cobble together a metal bench. I've made a couple other torsion box benches in the past and they really have held up great, I'll just make this one a lil beefier. This is my goal in SketchUp:
Purchased baltic birch ply yesterday for the skins, and just got back from Lowes (first tried Home Depot but their stock was wet crap
) with some decent 2x4s for the core material. Basically followed the idea from Tom's Torsion Box Workbench
for joining the upright sides to the back, but will use 2x3 angle iron to attach the top.
They can be made mobile/levelable with some of these
, must have for me in this case...
Good luck in your quest...