Mild steel rigidity

I wonder if someone can advise a total novice on what would be the optimum thickness of a 1200mm x 600mm mild steel sheet.

When I say optimum thickness I'm talking about using it as a worktop and storage shelf. It would be supported on all four sides only.

So what I really need to know what sort of thickness would be rigid enough not to bow, without being impractically heavy?

As i said before, I've no experience with sheet metal, so I've no idea.

Somewhat depends on the weight of items placed on the shelf/bench but 3mm may suffice.
A central bar in the 1200mm length would provide better support.

Emgee

A sheet of wood with a metal sheet on top would probbly do better

Kitchen tops are about 2 inches thick, once you get past 50 kilos a centre support makes things safer

A couple of bits of angle iron across the gap would help but they usually come in 1000mm lengths

Mr Brunel used steel box sections for one of his longer span bridges

My Argos desk has hollow 1 inch square box lengths 4.5 feet long and they make a big difference to stiffness

Just depends on the weight you expect it to bear

Edited By Ady1 on 24/05/2023 20:00:12

My big steel bench is 6 ft by 32 inches, somewhat larger than yours will be. The top is 8 gauge, approximately 4 mm. Frame is 2 1/2 inch equal angle with lots of weld holding the top on. There are two cross braces dividing the top into 2 ft by 32 inch bays. Horizontal bracing bars around 6 inches up on side and rear but it's open at the front. I've filled the space underneath with drawer sets on tiny rollers so they can be pulled out. Drawers and sliders stripped from redundant Civil Service filing cabinets.

I find mine solid with minimal flex when something heavy is dumped on it. Unlike ones of lighter construction.

From my experience I'd say that a 4 mm top with a cross brace across the middle will be fine providing its well tied down to a solid frame.

The man who made mine knew his stuff when it comes to welding because it sits flat and true on the frame with no distortion. Not a trivial matter to achieve.

That said Ady1 makes good point about using kitchen worktop to provide stiffness with a thinner top. But I'd still not go below 2mm for the top.

However you make it don't weld or do hot jobs on it the sheet will move.

For hot work get yourself a vermiculite sheet to protect the steel. Its OIK to hold stuff in vice for welding but do think of splatter.

Clive

Emgee and Ady1, thanks very much, that's given me a much clearer idea.

The top of my hydraulic lifting trolley is about 3ftx2ft and about 2mm thick It is well bowed by the previous, warehouse?, use.

Sheet metal, even thicker variety, is not suitable for weight bearing on shelves. It needs an underlying framework etc to support the weight with the sheet metal on top to form the flat surface.

Framework can be as simple as some pieces of sheet metal bent into angle "iron" and attached to the top to reinforce it. Or it can be heavier angle or square tubing or wood etc.

Supermarket shelves are a good example. They are about the size you need, made from about 1.5mm thick sheet steel. But the sheet steel is bent over into a 25mm square all the way around the edges and there are several reinforcing pieces of sheet-metal-angle spot welded across the shelf on the underside to take the weight in the middle. If you can buy old ones from the scrapyard they make excellent workshop shelves.

Sheet metal, being thin, is weak wne subjected to a load on the dlat surfaces.

Not surprising, since the stiffness is (B x D^3 ) / 12  With D being only a few mm the sfiffness has to be very low.

Using something like kitchen worktop with thin steel as a protective layer is much better.. Although, unless you are moving sharp edged metal axcross it frequently, using the worktop without the steel protective sheet may not be necessary.

My shelving (Wood, ex house bargeboarding ), survives having a metal box containg a HV6 Rotary Table and accessories, (Probably 30 Kg ) )being pushed on and off without beingcoming scored

If you do use just the sheet steel, it will need support, in the form of angle iron, or box section, to divide the unsupported parts into small areas. For any great weight to be carried, I woulds suggest no more than 150mm square. Even then concentrated heavy loads will permanently bend the thin steel.

And then you need to think about the strength of the framework that carries the shelves!

You don't want the framework carrying heavily loaded shelves to collapse!

Howard

Folding the all edges to make a flange, say 25 mm deep, will stiffen the shelf, but not prevent it bowing in the middle where it is unsupported, causing the outer flanges to bend outwards..

Edited By Howard Lewis on 25/05/2023 06:59:42

My little welding table is a piece of 6mm steel plate about 500 x 600 and is supported at a single point. It's rigid enough for its purpose.

I have a commercially made steel workbench. As I remember, the top is about 1/8" thick. It was not rigid enough, especially where my bench vice mounted. I cut down an old solid core wood door to fit under the bench top. It was about 1 3/4" thick. Rigidity problem solved.

John Reese

Thats interesting. Confirms my feeling that anything under 4 mm - 8 gauge would be too thin for a bench top without lots of extra support. Difference in sheet stiffness between that and 3 mm - 1/8" is, subjectively, considerable. Not that I've ever been in apposition to make proper measurements.

My bench has an extra cross brace at one end to help support the vice. One fastening bolt goes through the side frame and the other side bolt goes through the extra brace. I added significant re-enforcement between the two were the third bolt goes. After 35 years or so I'm blowed if I can remember exactly what I did for the third hole and I'm certainly not going to pull stuff out for a look. But out was cleary effective as my big 5 1/2" jaw Record vice doesn't vibrate, twist, tilt or attempt to move without taking the bench along.

Clive

Many thanks for all your replies. It's told me what I suspected, namely that a steel top is not suitable without support.

I was having great difficulty find this information elsewhere.

I'll use a wooden base.