ACME Thread shear strength Calculation

[JM7]

Hi,
I am designing a closure for a thick walled pressure vessel.
The closure is to be held in place by 4.75-4 ACME threads.
I have found a formula in the Machinery's handbook 28th edition. Page 1828. For the shear area of acme threads.
Shear area= 3.1416 D₁max [ 0.5 + n tan(14.5°)(D₂ min - D₁ max)
D₁ max = Max minor diameter of internal thread
D₂ min = Min pitch diameter of internal thread
For the 4.75 inch nominal diameter ACME thread with 4 tpi. I get very short thread lengths.
For a shear yield strength I have been using 1/2 the material yield strength.
Does anyone have any experience with this calculation or know of another source that I can check my work against?
I would greatly appreciate any information and or suggestions on this topic.

Thank you!

 

[desertfox]

Hi

Using 0.5 yield stress for max shear failure is fine just remember to put a safety factor on it.
See this link and scroll down till you see the chapter stress analysis.

http://www.ejsong.com/mdme/memmods/MEM30009A/lifting_systems/power_screws.pdf

 

[JM7]

Hi Desertfox,

This was very helpful!
I checked my numbers using this information and looks good.
Thank you very much for your help!

Mechanical Engineer
Vermont, USA

 

[desertfox]

Hi

Your welcome!