Torque Valve for Plastic Spacer into Metal

I made some computations to estimate the possible limit torques using values from different sources since I do not know the mechanical properties of the PA 6.6 used by Bossard. I came to the result that under circumstances the limit torque can be as low as 4.5 lb.in. The limit torque is the value which shears the standoff threads.

This value depends on:

- real full thread contact length between stud thread and standoff thread. chamfers on both parts have to be considered.

- tool used for the tightening, if the tool is too fast an over tightening can occur ie the actual torque can be higher than expected. If the tool has as limiter a sliding clutch it will better react than a cut-off tool.

- if the friction coefficient during your tests and the one to be found in production differ (if in production friction is lower) the pre-load for same torque will increase and bring the assembly nearer to its limit.

- tolerances for the stud OD could be too big which reduces the nut (stand off ) portent capacity.

So that is seams that you should compare :

- tightening method and tools used for

- assembly tolerances to check true contact length

- assembly conditions for test and production.

It is most probable that you are both right only the conditions differ.

If you can get more input concerning geometry and mechanical data for the PA6.6 I can verify where is the torque limit.

Hope it will help