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I'm trying to use motor-sizing tool developed by oriental motor to choose good servo motor for my cnc

The tool requires breakaway torque of my screw as input, I searched online but I got people measuring it using wrench.

I'm working on simulating the machine before I buy anything so I don't have the screw to test anything on i.

This is the screw I want to use and all the specs are available in the link, I need to calculate the breakaway torque mathematically so is there any way?

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You can approximate the breakaway torque by considering static friction only. From the static friction coefficient of the lead screw (by knowing the maximum load on the spindle, coming from the application) you can calculate the static friction torque of the nut on the lead screw.

You should do the same with all linear guides and/or bearings that you have and sum them up. That will be your breakaway torque.

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  • $\begingroup$ So what is the formula? $\endgroup$ – Ammar Atef Oct 27 '16 at 5:28
  • $\begingroup$ For the lead screw: F = c*N where F is the static friction force, c is the static friction constant and N is the normal force. In this case you have to convert the Force to Torque Torque = Force x Lead /2pi. Or the lead screw manufacturer might give directly the constant which links static friction constant to torque. $\endgroup$ – 50k4 Oct 27 '16 at 6:07

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