torque / pressure calculation - essentials

[cervantes]

hi,

hypotetical situation:
there is a brown part, with blue on one end, then squeezed with head of screw
screw was tightened with 30Nm torque

1) how to estimate "push" of the screw head against blue part?
2) how big torque should I apply to blue part to rotate it after it is tightened by screw (also 20 Nm ?)

thanks mates!

C

 

[rb1957]

1) bolt preload, P = 5*T/d ... average typical "rule of thumb" value

2) you want to rotate the clamped up blue part ? if you want the blue part to rotate you should add a sleeve/bushing so that the bolt clamps up on the sleeve and not on th eblue part. if you don't want the blue part to rotate, the clamp-up to the brown part will create a fair amount of friction torque; to be sure, it'd be better to have some anti-rotation device, like a second fixed point.

Quando Omni Flunkus Moritati

 

[tbuelna]

cervantes-

You have not provided enough information to answer your question. The precise answer to your question is quite complicated, and will vary greatly depending upon factors such as material stiffness, frictions at the contact surfaces, precision of the screw threads, etc.