I have 6 lathes & one is a Model A. It sits on a 2x4 frame & a piece of 1/2" plywood. The other lathes are heavier & I used 2 pieces of 1/2"...JER
I used 2x4's on a few of Mine too. I have a corner bench that runs the full length of one wall and 3/4 of the length on the other wall. I basically laid them out, and built the top frames like a 29" tall wall would be framed, (on the ground). I then leveled & screwed a strip of have inch ply to the long wall studs in the shop to use as a ledger board to hold the inside of top's frame level while I screwed It into the studs of the wall, then I chopped some legs out of 4x4's to support the front of the bench. Then ran a level the other way, and screwed the legs into the corners of My top frame from 2 sides. On the other wall the top wasn't as long so more manageable, and I didn't need a ledger to hang It, I simply butted the end of that top up with the front of the other side and screwed the frames together. That really made the frames stronger, but the 3/4 ply I used for the top, made the whole thing rock solid. Not portable at all, but It's super sturdy. That bench only holds a deluxe on the long side, and a small milling machine on the short side, It's stronger then I need for the equipment mounted, but I have much confidence that It would hold much anything I would decide to put on them. I have another shorter bench with My panto setup, and It's basically the same framed top as the others. but has a 1/2" ply top instead of 3/4, It only holds a panto, but would be enough to hold the somewhat lighter equipment i have on the stronger bench.
The 3/4" ply was what I had, and was straight. It seems to be about the same as doubling 1/2", but the main thing is either will make a sturdy bench if built well. I would have doubled them up too if I hadn't had that 3/4 to waste on something like this anyway. I'd probably use some kind of adhesive if doubling up though, just to take advantage of the extra strength of a lamination.
Anyway to sum up, I agree with you, a single sheet of 1/2" over a framed top will get someone by fine with the lighter weight cue specific or repair lathes, but yes, if you start getting into the ton ranges in weight It's gonna take 3/4 on up to feel confident, depending on just how heavy the machine is. The sturdier the better in My book. Better to over build a bench for what It will be holding instead of under doing It, and have It sag to one side or worse, come crashing down one day.
Building on those carts like that though to hold the lathes mentioned shouldn't take anything terribly thick, if there's a good frame in place. A wood frame would probably work fine too, but I have a small welder, so If there wasn't already a easy way to mount a table surface, then I would probably weld a frame from straight and angle steel or something to hold some thick or doubled up plywood, and bolt or weld the frame to the cart. Might be better to bolt though, If needed could back one side of the bolt with a steel plate so It doesn't deform or distort the sheet metal on the cabinet Itself.
Also A while back there was someone selling a really thick top material to use on router table and such, It may would be perfect for this, may be a hair costly though. I'll see if the stuff is still listed on there, and if so will post here.
Greg
