We want to figure out how much torque to use on what kind of fastening.

Too little torque makes things too loose.

Too much torque can break things and also plasticly deform metal (leading to unwanted drift).

1/4-20 screw fastening an aluminum base

We often use the Thorlabs BA-2 or BA-3 base for mounting optics. How much torque to use?

1. We want to use a steel (18-8) washer (rough side down) and a steel (18-8) screw to hold it down.
2. The washer is needed to increase the maximum possible force for fastening without getting in to the plastic deformation regime for the aluminum base.
3. We want enough torque, such that, with the 3-4 threads available for a 1/4-20 screw in a standard optical table with stainless steel top, we are elasticly deforming the screw and the aluminum base.
4. To prevent creep, we want to stay at a stress level of ~50% of the plastic yield limit.

Good collection of torque wrenches for optical laboratory use

1. Ball Driver (1/4-20) to give ~5-6 foot-pounds for fastening things with washers on optical tables.
2. little wrenches for the little screws on optical mounts.
3. 5/16" allen wrench for SMA cables.
   1. open end, crescent wrench

      1. Fairview break-over SMA Crescent

   2. over-the-cable for connected SMA cables in a high density panel
   3. ball-driver attachment, over-the-cable. Combines with a small ball driver torque wrench.
4. others?

More Info

• Torque Specs for various cable connectors 5-7 inch-pounds is a good number for steel SMA connectors.