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