Help Calculating Shear Stress 2

[RohitGogna]

Hello,

I am trying to calculate the shear stress on the bolt in the attached picture. This is just so I can confirm on paper that a 0.25" cap screw bolt is strong enough to withstand the applied forces at the pivot. Can someone please help guide me on how to calculate the shear stress at this point? The reason as to why I am trying to calculate the shear stress is because this bolt at this location has had several repetitive failures in the past where it has been sheared.

I believe I have all the variables I require to solve this problem but am not sure exactly how to approach it.

I originally believed I should have used the equation:
max tau = (16*F)/(pi*d^3) but soon learned that this equation is used for rotating shafts. In the attached image the rotating arm is at its lower limit and is unable to rotate further.

Any help would be greatly appreciated.

 

[Tmoose]

Hi RG,

You said "Yes the bushing also has a flat surface on the end with rounded corners".

The best shape for the bushing where it contacts the plate is very flat, with the corner simply deburred with the minimum chamfer to clear the corner of the counterbore I'm suggesting in the plate. If the end of of the bushing is flat within 0.0005", but slightly convex, then the bushing will only contact a small region in the middle around the bolt clearance hole, and rock relatively easily, again subjecting the bolt to bending loads.

Dead Flat or slightly convex is a requirement for the bottom of the new plate counterbore as well.

HSK type machine tools rely on face contact for their superior bending resistance.
About 1/4 of the drawbar force compresses the hollow tool taper, and the rest clamps the tool and spindle faces together.

https://www.youtube.com/watch?v=SE6yC-vqoRY

The tolerances for the accuracy of the mating spindle face are pretty low. See attached image.

The spindle shaft is in red, and the HSK tool is yellow in this video.

https://www.youtube.com/watch?v=SE6yC-vqoRY

The value of utilizing clamped large diameter face contact is shown starting 1:45 here -

https://www.youtube.com/watch?v=uXU0GzATIig

 

[BEMPE16524]

RG,

Well done! Share with us your final rectification plan and result.