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 Power Screws and Force Post Reply Forum
 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 3-pronged 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 pre-tensioned 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)/(1-mu*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 pitchFor 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 inch-10 ,the term in parentheses above is: (0.1/pi/.5+.11)/(1+.11*0.1/.5)=0.17 The torque equation is then: T=0.17*.5*DF=.085DF which is considerably lower than the the formula you cite and would give a less conservative result. It should be noted that if there is bearing friction during the torqueing process it would increase the T somewhat.