[Cartierusm]

I've got a linear bearing situation where an extension spring will have about 500 pounds of force pulling on it. The linear bearing can adjust up or down to increase or lessen the force of the spring. I was wondering if anyone can tell me if a 3/8" Diameter 316 Stainless Steel Shaft can handle the amount of force or it will bend. See the pic below for an example.

[cadfish]

every thing bends under a load, how much deflection will you tolerate? I am not an engineer, just read the books for fun (yes I am very strange), I just looked it up and did the math and I calculate that the deflection at the center of the rod is about 0.00483". Is there an real engineer to back me on this? (500 x 2.342^3) / (48 x 28,500,000((pi x .375^4) / 64))

[Cartierusm]

Well, thanks. So you're saying that for 500 pounds of force on a 3/8" Stainless Rod that is 2.342" long the deflection is 0.00483"? That's not bad, I think that would work.

I guess my question really, which I didn't explain, is would 500 lbs bend this rod permanently? If the deflection would not hinder the linear bearing from sliding I would say it's a go?

[cadfish]

From what I understand is that once it passes the yield point it will not return to shape. The yield point for SS316 is 35,000psi and SS316L is 30,000psi. I am thinking its a go. But I could do the math later and see how much stress it will actually have.

[cadfish]

uhh ohhh, I calculate the max stress as 56515.444, (500 x 2.342) / (4 x .00518)
Is there a professional engineer who can give us an answer?

[Cartierusm]

I appreciate the work you are putting in. Maybe I should look at a harder steel? Any suggestions? I'll check out what Mcmaster Carr has in terms of round stock.

[Cartierusm]

I was just doing some research and Mcmaster has some 17-4 Stainless which has a yield strength of 118,000 PSI, that should do, right?

Here's a link. http://www.mcmaster.com/#9095k107/=4c87ow

Cadfish, is there a page somewhere where I can read about how to calculate what you are calculating for me? Thanks.

[cadfish]

Do you have a Machinery's Handbook? They have about 300 pages with these formulas and properites of materials they even give sample problems explaining how to use the formulas. If not you can try this.

http://www.engineersedge.com/beam_be...m_bending2.htm

They have an explanation explaining the terms bellow.

[achavarria]

Yes, cadfish is right. The shaft will bend around 0.004 in.

[achavarria]

When I calculated, I use a formula from any stress and strain text book. I use a two bearing supported shaft. The formula for the max deflection at the center is
dx=(PL^3)/(48EI). If you change the steel, the modulus E will not vary a lot, you will not gain much using another steel. I you want less than 0.004 I suggest to increce the diameter of the shaft.

[Cartierusm]

Good to know thanks a lot. I'll stick with the 316 as I have a ton of it.

[achavarria]

You welcome. Any other question in Mechanical Engineering, please let me know and I will help you.
Arnoldo

[martinw]

You welcome. Any other question in Mechanical Engineering, please let me know and I will help you.
Arnoldo

Dear Arnoldo,

I think you used the deflection formula for a point load at mid span. My guess is that the length of the linear bearing and its housing is quite a large proportion of the the total span, and that the bearing and housing will actually "support" the shaft. The actual deflection could be quite a lot less than the one you calculated. Just a thought.

Best wishes,

Martin

[Cartierusm]

Thanks, I will have to get a machinery handbook one of these days they are just so expensive.

[achavarria]

Dear martinw.
You are right. Is the 0.004 in defection is acceptable then less than 0.004 in will be better.
Truly
Arnoldo