Heavy duty table design(>750kg load?)

[MrCrankyface]

I'm working on a new workbench for my garage(workbench thread) and wanted to see if anyone had some input for wooden frame design.
Originally I was going to go with a steel frame under the heavy cast iron plates but money is low and steel is expensive.
Hence I've started thinking about making a wooden frame instead, I made a quick sketch of what I was thinking, using C24 classed 45x145mm lumber.


The frame will be 800 deep as the plates are, the granite plate is only 600 deep and will have a support beam infront of it.
The cast iron plates weigh around 200kg and the granite is 76kg more, so the empty frame needs to support around 480kg as is.
The biggest thing I can imagine putting on this table is the table from my metal mill, which is probably 150kg, so let's say 250kg for the sake of caution.

We're now talking nearly 750kg load on a wooden frame.
Does anyone have experience with a wooden frame holding up such heavy loads?
I felt optimistic about 500kg, maybe doubling up the timber etc but 750kg suddenly feels like a lot.

Would love to hear if anyone has tried anything similar!

 

[Martin W]

Maybe square it all up with a plywood shell, to make it more rigid.
Cheers
Martin

 

[MrCrankyface]

Yeah I was considering inlaying a sheet of plywood ontop of the 45 degree bars, to stiffen up the entire back, top and sides.
The front will remain open so I can install drawers for storage.

 

[Eddyde]

I would make the entire bench out of plywood, double thick (¾" 19mm) on the sides and the middle, single thickness on the back, then set in two steel cross beams across the top front to carry the front of the plates.

 

[mattthemuppet2]

here's mine on the inside


4x4 for the uprights and most of the front to back braces, 2x6 on edge for the top supports (doubled up 2nd from left, single layer at the ends, just a 2x4 on the 2nd from right and 2x4 running horizontally. 3/8" plywood screwed to the sides and a hodge podge screwed to the back, which is then screwed to the wall joists. The center and right tops were a bit bouncy, so I removed them before putting my SB9 up there and added another layer of 3/4" MDF underneath the 3/4" particle board countertop.

It doesn't move, make any noise or seem to really notice what I do to it. Didn't make a peep with the South Bend up there and that's supposed to be 750lb crated, so maybe 500-550lb (~260kg?) as is.

Wood is crazy strong in compression, so most of the weight should be born by the vertical elements of the bench. At the span you're looking at, a doubled up top (2 layers glued and screwed together) over construction wood horizontal supports will be fine. You could add diagonal bracing but an outer plywood shell will be plenty enough to resist movement if the rest of the structure is sound.