1. Horizontal Rod Size Required

Many, many years ago I graduated college as a Mechanical Engineering Technologist but my career path took me elsewhere. I therefore can use and comprehend most of the "tools of the trade" but I'm very rusty in that usage. I therefore don't feel fully confident in my own calculations and would like some input.

I want to use a 12" long Stainless Steel solid rod to support approximately 200 lbs of weight equally distributed between two mounted bearings on each end with the rod itself only supported in the center.

In addition to the rod supporting the weight, it needs to remain straight enough that the bearings do not bind due to a bend in the rod.

For unrelated reasons the rod cannot exceed 2.375" diameter But I'm hoping the actual required size is much less than that.

I'd appreciate either an answer with some supporting calculations or a link to somewhere the info can be found.

2. Thanks Kelly but been there done that and it doesn't answer the question.

3. Originally Posted by sigmatics
Thanks Kelly but been there done that and it doesn't answer the question.
You want somebody to do the work for you then?

Also, check out the following: Critical Speed Bearings Equations and Calculators

4. You misinterpreted my answer. I meant that I'd already long ago done all the calculations that your first link provided and none gave me anything that indicated, in my opinion, an answer as to the rod size required.

Your second link is irrelevant because the bearing speeds aren't what I need to know about (FYI: the bearings are there for ease of movement and run irregularly at under 1 rpm). I need to know what distortion of the bar (or shaft) would cause the mounted bearings to bind due to their becoming misaligned with one another.

If I am incorrect in either of those statements then I'm asking for you or someone to tell me how to derive my answers from the results of those formulae or to point me to formulae that actually do.

5. Originally Posted by sigmatics
You misinterpreted my answer. I meant that I'd already long ago done all the calculations that your first link provided and none gave me anything that indicated, in my opinion, an answer as to the rod size required.

http://www.engineersedge.com/beam_be..._bending20.htm

and... yes you do need to know what the critical speeds and resultant deflections are.

6. There's a difference between something be useful vs helpful. Those equations I originally pulled from my Mechanical Engineering Handbook and they were definitely helpful for what I'm working on they just don't seem to give a definitive answer as to the required bar diameter. I'm not even looking for an exact diameter just an approximate minimum so that I can trust that a slightly larger size would be effective.

As I mentioned the bearings won't be moving at any significant speed that would make any difference in my opinion but my opinion, as mentioned, is somewhat rusty. Can you tell me why you believe otherwise.

7. The webpage has everything you need - seriously. You are clearly way out of your element on this one. Do you have an engineer at work that can help?

8. As I mentioned I haven't worked in the field in many years and if I had a co-worker or friend or whatever to ask I wouldn't have needed to ask the question here but obviously I'll just have to continue on my own. Sorry to have bothered you.

9. Kelly, what I think he needs is a calculation that will give him the angle of the rod at the bearing locations due to the deflection of the rod, assuming he already knows the allowable angular deflection for the bearings from the manufacturer. Do you have a reference in your vast library for that?