How to Calculate Clamping Force of a Screw

Screws, like bolts, are derived from the simple machine known as the inclined plane, which raises a load vertically by moving it horizontally. Think of the threads of a screw as an inclined plane wrapped around a bar. As the screw is turned, the threads force it into the material. Friction holds the material against the threads, resulting a measurable force known as the clamping force. It is determined by subtracting the tension force, which is the force that pulled the screw out of its material, from the preload force, which is the force used to turn the screw.

Screw
Wood
Force transducer
Torque wrench (optional)

Instructions

- 1
  Measure the preload force. This is the force that is exerted on the screw to tighten it into place. The preload force can be measured directly with a force transducer. It also can be derived using a torque wrench and dividing that measurement by the number of threads and the value K, which is the tightening factor derived by the manufacture of the screw or bolt.
- 2
  Measure the tension force of the screw. This can be determined by using a force transducer. The tension force measures how much force is exerted by the material to force the screw out. It results in friction against the threads of the screw.
- 3
  Subtract the tension force from the preload force. This final value is the clamping force.

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