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Power Screws and Force  
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Posted by: mike22 ^{®} 09/24/2004, 07:10:06 Author Profile Mail author Edit 
I have a device that I need to estimate a failure torque for. It is a 3pronged wheeler puller, with an extra base, to clamp it all together. Basically I have a power screw on it, which is tightened with a torque wrench. The screw is then in compression. Is the compression in the screw given by T = 0.2DF, or is it the much more complicated power screw equation I have seen in books (is generally given as T as a function of the Force, the lead, the pitch, etc...). Or are the two equvalent, with the 0.2 using standard values?? I seem to remember the T = 0.2DF having something to do with pretensioned screws, but the /calculators/torque_calc.htm page suggests different. thanks! 
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Re: Power Screws and Force  
Re: Power Screws and Force  mike22  Post Reply  Top of thread  Forum 
Posted by: zekeman ^{®} 09/24/2004, 13:43:09 Author Profile Mail author Edit 
I'm not crazy about using "empirical" formulas for this.
I would use the basic approximate formula: T=F*{(tan(alpha)+mu)/(1mu*tan(alpha))}*.5*D where: alpha=the helix angle of the screw=invtan( p/(pi*D) mu= friction coefficient D=pitch dia of screw p= screw pitch For example if the screw/nut is lubricated and steel/steel, the approximate low end friction coeff=0.11 and if the screw is an acme 1/2 inch10 ,the term in parentheses above is:

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