Force calculation of sphere against plane
Force calculation of sphere against plane
(OP)
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,
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,






RE: Force calculation of sphere against plane
RE: Force calculation of sphere against plane
RE: Force calculation of sphere against plane
Yes, I'll check the statics. and each component. This is not the problem
What I need to know is what happens in between these two parts (spherical and planar)
Cheers,
RE: Force calculation of sphere against plane
The allowable stress is defined by the code in effect. It should be at least 3-4 times the allowable stress in tension.
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
RE: Force calculation of sphere against plane
Regards,
Brandon
RE: Force calculation of sphere against plane
RE: Force calculation of sphere against plane
RE: Force calculation of sphere against plane
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Force calculation of sphere against plane
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Force calculation of sphere against plane
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Force calculation of sphere against plane
Thanks for the answers
- The xcalcs page is very cool. I made some analysis and I got the following results:
Average compressive stress: 1340 MPa
Maximum compressive stress: 2010 MPa
The contact is steel against steel. Supposing a yield strength of 200 MPa I'm out of the 3-4 times
- I don't have the Roaks but I found other info. For instance:
htt
(but I don't get the same result in the equation 11!)
- I need to have the flat surface, this is an accurate alignment system where these feet have to slide on the flat surface.
Cheers
RE: Force calculation of sphere against plane
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Force calculation of sphere against plane
RE: Force calculation of sphere against plane
RE: Force calculation of sphere against plane
This system is already manufactured and working.
I didn't realise the materials we were using
For the plane (plate) is 16MnCr5 which has a minimum tensile strength of 1000MPa
For the sphere (screw) the quality is 10.9 so 940 MPa
I'll do the calculations, but I'd like to ask someone to check the example in
htt
I think it's wrong!
cheers,
RE: Force calculation of sphere against plane
if it's working, don't run a calc on it !
RE: Force calculation of sphere against plane
we want to know if we can put more weight on it; much more
RE: Force calculation of sphere against plane
E' should be GPa, and a deformation of 1.4 mm under 10 N is ridiculous.
You didn't specify your dimensions for us to check.
Anyway consider that a structural code will normally allow for a permanent deformation under the sphere, but this is of little importance in that case, as the spherical support will normally not move.
In your conditions you risk to degrade the flat surface by the repeated local deformations by the moving sphere, so you should consider a lower allowable.
You should look into the allowables for ball bearings, that should be (maximum stress) of the same order as the fatigue strength.
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
RE: Force calculation of sphere against plane
I contacted the author of the paper and he agreed there are mistakes.
I have a 50 mm Radius feet (10.9 quality) against a 16MnCr5 plate
The point is I can't say how much weight we place, but what's the maximum one
cheers,
RE: Force calculation of sphere against plane
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, ...).
RE: Force calculation of sphere against plane
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
RE: Force calculation of sphere against plane