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Message: <blockquote data-quote="Truename" data-source="post: 9814149" data-attributes="member: 78255">I tested the plywood, so I know it's solid, but how much weight will the aluminum rails take? I have a lot of choices for size and weight.The 80/20 catalog gives this formula for how much weight a rail can take:(L^3 * W) / (48 * E * I) = DL is length, W is the load in pounds, E is modulus of elasticity, and I is moment of inertia, and D is deflection in inches. E and I are provided in the catalog, so I can use this formula to calculate how much weight a rail can take before bending too much.Originally, I was thinking I'd use 3"x0.75" rails to support the plywood. But when I ran the numbers, assuming a maximum 1/4" deflection and 43.7 lbs for the plywood (its actual measured weight), those rails would only support 36.8 additional pounds. The load would be spread out by the plywood, and there are multiple supports, but I don't know how to calculate that. It doesn't seem like it would be enough handle a person standing on the table.So I went to the next size up: 3"x1.5". That can support 494.7 extra pounds with a standard rail and 327.4 extra pounds for an ultra-light (cheaper) rail. With a 3x safety factor, that gives me between 109-164 pounds. With a 1" deflection, that increases to 445-670 even with the safety factor. Given that the plywood will spread the weight, that seems like plenty.But I'm not an engineer, so I chose the standard rail rather than the ultralight, just to be safe.A similar calculation went into the edge rails. The longest edge can only support 142 extra pounds at a 1/4" deflection (no safety factor). But the worst somebody will do is lean on them, and they can take up to 65.5 extra pounds before they flex as much as 1/8", and that's not accounting for the load being spread out by the plywood. That seems super stable. Worst case, if someone walks on it, they'll support 302 extra pounds (with a 3x safety factor) at a 1.5" deflection.Finally, the legs. I'm using 1.5"x3" legs so I don't have to worry about cutting notches in the plywood and mat. I'm a bit concerned about the legs supporting such a large table, though. I'm sure they'll be fine vertically, but what about people pushing on the table?I treated the legs like a cantilever, which I'm not sure is correct. The formula for a cantilevered load, according to the 80/20 catalog, is (L^3 * W) / (3 * E * I) = D.A shaky table would be super annoying, so I limited the max deflection to 1/8". That leads to a maximum of 126.4 pounds of horizontal force in one direction and 462.2 pounds of force in the other (no safety factor). I think that'll be okay. If someone runs into it hard, the legs will flex more, but that's no big deal. It'll only flex 1" under 1,011 pounds of force. That should be nice and stable.I'm probably overbuilding this, but I knew that going in.PS: In case it's not obvious: I am not an engineer! If you decide to build your own table, you're responsible for your own safety calculations. Don't use mine, they're probably completely wrong.</blockquote>

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