Screw Torque

Screw Torque
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Posted by: tom0067 ^®

09/26/2006, 11:26:49

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Seems like such a simple thing, but I am having a difficult time locating a recommended screw torque for an M2.5x0.45 machine screw which will clamp a PCB to a diecast aluminum heatsink with threaded holes.

Anyone have a good reference to consult or recommendation?

Modified by Administrator at Thu, Sep 28, 2006, 13:09:26

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Re: Screw Torque

Re: Screw Torque -- tom0067 Post Reply Top of thread Forum

Posted by: TZA ^®

09/28/2006, 13:35:07

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The generic procedure for any screw is in Shigley and Mishke's Mechanical Engineering Design, although there are common lookup tables from vendors, etc.
Generically, get the proof strength of your screw (Mcmaster Carr probably has it). The recomended preload (as force, not torque) i believe is 75% of proof strength for reusable screws. Use the screw equations to translate from force to torque. The rule of thumb version, Torque =~ .20*Preload*screw diameter. Watch out for units!
Make sure you check the shear force of the thread in the heat sink too, assuming your screw is not aluminum!

Modified by TZA at Fri, Sep 29, 2006, 15:49:15

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Posted by: devitg ^®

09/28/2006, 10:07:51

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from the PROTO tools catalogue
for a class 4.8 grade, it shall be 1.05 Newton-meter
9.8 2.20
12.9 3.29

Modified by Administrator at Thu, Sep 28, 2006, 13:07:36

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