Specification for Screw Torques

Also, check the website for Assembly magazine, http://www.assemblymag.com, they have some good information on the basics of torque. Determining the "correct" torque value can become very complicated very quickly. The same size screws made from different materials would need different torques due to the differences in the coefficient of friction of the materials and the strength of the material.

The materials being fastened together are also a major factor in determining the appropriate torque values. Most board materials will tend to deform, or cold flow, often within a day or so, and the clamping force will drop.

Never consider changing to a higher rpm torque tool as a way to speed up the process. Depending on the materials of the various pieces involved, heat from friction could cause a lot of problems. Also, the momentum generated by the tool's motor and geartrain will cause a wider range in final clamping forces, usually higher than what the tool was set at. You could also just shear off the head on a small screw.

There are no easy answers, There are about as many factors affecting hardware and torque as there are affecting the quality of a solder joint.

Mike F.

reply »