Force calculation of sphere against plane

[davidrdguez]

Hi there!

I need to check the maximum weight we can put on a platform we have.

There are different parts between this platform and the floor. It doesn't seem difficult to check each part, but the platform is place on the top of three feet like the one in the attached picture: a sphere touching a plane.

In theory the sphere touches the plane in one point.

How can I know the maximum load?

Thank you
Regards,

 

[rb1957]

the problem with "maximum" is that it is hard to calculate with your design; as i see it.

any load is deforming the plate (or sph.) since by analysis you have a point contact = infinte stress. in reality you have some localised yielding = load distribution. but clearly too much local yielding will impact how easy it is to move, degrade the palte/sph., etc ... qualitive requirements. (plus somewhere along the line the structure on the other side of the feet is going to give way.

the easiest thing would be to test a structure,
next easiest would be to redeisgn the feet so that they only stand (the way the great designer intended feet to work) and something else comes into play when moving (castored wheels, a dolly, ...).

 

[prex]

Some information here: thread404-95671

prex

http://www.xcalcs.com

: Online engineering calculations

http://www.megamag.it

: Magnetic brakes and launchers for fun rides

http://www.levitans.com

: Air bearing pads

 

[dhengr]

Again, you will get deformations with any significant loads. It’s a fact of life. But, a possible solution to your problem is as follows: take a 3 or 4" square piece of like material, 1 or 2" thick; the bottom surface is machined flat and polished, the top has a .25" deep spherical hole machined in it to a radius of 50.1mm for your leveling foot to fit into. If you’ve done the recommended reading on this subject, as suggested above, not just finding a formula and plugin-n-chugin into it, you should know that the nearer the two spherical surfaces are in their radii the lower the bearing stress will be, and the less the deformation will be. This will allow you to load the leg to a higher value, without it deforming significantly, and will distribute that load to the base plate to keep it from being deformed by the leveling foot radius. You figure out the exact sizes, stresses and deformations.