Calculating Shear Stress for Thread in Hydraulic Press

[inquist]

Shear thread formula?

my group has been told to figure the shear stress of a thread for a hydraulic press which pushes at 100t, we have figured it will pull at 30t using the ratio of the areas from the pistions.
just we need to figure the shear stress on the thread if it was to pull. we don't know what formula to use.
any help would be appreciated.

 

[Astronuc]

Does one have access to a Machinery Handbook? Perhaps one can try the library or one's department.

Here is one example.
http://www.roymech.co.uk/Useful_Tables/Screws/Thread_Calcs.html

and another
http://www.tribology-abc.com/calculators/e3_6e.htm

But the answer will be geometry dependent, and I imagine the thread is rather thick for a hydraulic press, as compared to a bolt or fastening screw.

Quick and dirty answer from http://www.efunda.com/forum/show_message.cfm?start=1&thread=18428&id=18435

A = K*Pi*D*T where D is the thread minor diameter, Pi = 3.14, T is the thread engagement, and K is a function of the internal thread contact, which in worst case is 0.5 for square threads. Set stress equal to shear yield stress and solve for force, P.

But do it right!

 

[Cement Legs]

Why would you ever load threads in shear? Considering stress concentration risers you are always better off using shouldered bolts whenever possible. This is especially true when extremely large forces and/or health and safety risks are present.