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I am an occasional hobbyist "DIYer" (not an engineer) who needs help choosing a steel plate for a small home improvement project:

I will use it to create a 20" circle, suspended from a bolt at the center. It should be able to hold 350lbs pretty much evenly distributed over its surface.

There is already a generous safety margin built into the 350lbs estimate.

What is a reasonable choice of steel plate (steel type + thickness) for me to go with?

Just to be clear, this is not a critical application -- ie, no one will be hurt (fall/get squashed) if this fails.

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  • $\begingroup$ Welcome to engineering.SE! You may want to consider asking on diy.stackexchange.com for additional followup questions for your home improvement project. However, you have given all the information needed for solving this project, so +1! Thanks! $\endgroup$
    – Mark
    Commented Apr 7, 2017 at 22:35
  • $\begingroup$ Good engineering design is often based on thinking through situations that could happen rather than what we expect to happen. So a calculation-based answer to your question is mostly likely going to be entirely based upon what you expect the worst-case scenario of uneven loading on the plate will be. How far away from the center of the plate could the center point of the even load be? Could the load end up being more concentrated than you expect? Is it possible someone would try to step on the steel plate, or the object it is supporting? $\endgroup$
    – Rick
    Commented Apr 12, 2017 at 13:21

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By 20"x20" circle, I assume you mean 20 inches diameter. That puts the surface area at 314 in^2. So 350 lbf evenly distributed is just a bit over 1 lbf/in^2. That's a pretty small load. Although I've not done any calculations here, my intuition is that you can probably use 1/4" or 3/8" plate. If your project will be outside or otherwise exposed to moisture, stainless steel would be recommended. Otherwise I think any generic low carbon steel would be fine.

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  • $\begingroup$ The answer depends entirely on how much bending of the plate is allowable. In some situations, 0.25" at the rim might not matter at all. In others, 0.005" might be a disaster waiting to happen. $\endgroup$
    – alephzero
    Commented Apr 8, 2017 at 12:42
  • $\begingroup$ The minimum thickness of the plate may be irrelevant, unless the thickness at the center can withstand the shear stress caused by the 350lb load in the bolt. $\endgroup$
    – alephzero
    Commented Apr 8, 2017 at 12:44
  • $\begingroup$ Not to mention that a single bolt is an instability problem waiting to happen. $\endgroup$
    – Wasabi
    Commented Apr 8, 2017 at 13:40
  • $\begingroup$ @Daniel, thank you for this. Apologies about the 20"x20" mistake, originally I was thinking of using a square rather than a circle! $\endgroup$
    – lara michaels
    Commented Apr 9, 2017 at 1:56
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That is not much load. If it must be steel , I would find a local weld shop and go to see what leftovers they have; I suspect 1/8" would be good. Otherwise plywood could do the stated job.

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The weight on the bolt will be 350 lbs plus the weight of the plate. Depending on what size washer and bolt head you use the force at the hub/bolt overlap could be 700 psi. 1/4" plate is probably ok for the full disk, but I would double it with 1/4" thick by 3" diameter inner disk/washer.

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