Lead Screw nut Force vs drive Torque

[FONT=Source Sans Pro]Hello all, I'm working on an application that uses a lead screw to move a platform up and down, and also clamps down a workpiece, using a servo in torque mode. I need to achieve a certain amount of clamping force (30,000 lb), and I'm trying to figure out how much torque I need out of a gear box in order to achieve that force. I beat around with some trig to come up with a formula, and got a pretty bogus answer. I'm using flat threads, and I'm assuming no friction since there's no movement - I'm only interested in the clamping function at the moment. Can anyone point me to the right formula?
Thanks!! [/FONT]:)

Attachments - Diagram and scratch formula work

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