Steel plate

I plan to make a 30" by 29" countertop with steel. It needs to support 200 pounds (evenly distributed). The support under the sheet of steel is a 30" by 27" wood cabinet box. Will a 1/8" thick plate of steel be sufficient? How much will it deflect?

Without doing any math, I can tell you that a 1/8” steel plate will easily support 200 lbs evenly distributed with negligible deflection.

Throw a few 2x4’s across the top of that cabinet and you could use 1/8" plywood … 200 lbs doesn’t sound like very much … the weight of a decent sized man … so with enough bracing under it, the 1/8" steel ought not to deflect much at all …

I played with this calculator, which says that a 200lb point load in the center of the plate will result in a 1/3” deflection. An evenly distributed load should have minimal deflection.

Thanks. Sounds like no need to go to 3/16", or more.

For what it’s worth, my Roark’s textbook tells me that a 30x29x.125" flat rectangular steel plate simply supported at the edges with a evenly distributed, 200 lb external load, plus an additional 30.7 lbs of load for the steel plate weight, gives a max deflection of .163"

also, the deflection for a 3/16" plate with the same loading conditions drops to .05"

Why not just build the cabinet box with a piece of 3/4" plywood on top? Every countertop I’ve ever seen was built that way. Then the tile, formica, steel or whatever is laid on top of the plywood. You can then use any thickness of steel that you want, since the steel doesn’t need to provide any structural strength. I would think that a sheet of plywood (maybe $20) would be much cheaper than increasing the thickness of the steel, but I don’t know much about the price of steel.

It’s not just the defection, but how solid it feels. Even 1/8" may bounce or “clank” if you are using a chopping block on it. Install 3/4" plywood and glue it down and you can go thinner if you want. Restaurant stainless steel tops are made this way (over 1" or 1 1/2" substrate) and the SS is probably 18 gauge, well under 1/16".