Modified Torque Specs

A bit more info on the pinning and failure point would help.

Pin hole drilled straight thru the centre of the screwed rod ...or just catching the edge?

A 5/16" drilled hole in the 3/4" bar or tapped ?

If the threaded rod is just inserted thru a drilled hole and then shearing at the pinning point it's a bad design and 12 ft/lbs is way to much.


If the threaded rod is actually screwed thru a tapped hole and is shearing at any place other than the pinning point then it's probably end user abuse.

Woody

Place a hardened steel washer under the connector and torque once more. If the customer is over-torquing the fastener, the hardened washer will delay failure of the threaded rod. This solution puzzles me. I don't know why it works but it does.

If the threaded rod has die cut threads, substitute one made with rolled threads. Look at the threads of both under a high powered jeweler's loop and the reason for the superior strength of the rolled threads will be immediately apparent.

L.J.

Thanks,

Rods are rolled threads Failure was at the pinning point and pins are in the center of the rod. looks like both here and customer are over torqueing.

"Failure was at the pinning point " ..not surprising seeing as how you've weakened the 5/16" thread by drilling thru with a 3/16" pin thus effectively removing approx 70%? of it's strength!

Sorry,

It's a 3/32 pin (.093 hole) my error

OK.

So your clamp load is speced according to that of a 5/16"-18 low carbon threaded rod using a torque = 12 ft/lb's but your stress area has reduced to....what ....Ummm the equiv of 1/4" screwed rod? and therefore your clamp load is approaching the tensile strength of your stress area.

http://www.boltsupply.com/catalogue_files/catalog_data/toc_data/pdf/006.pdf

Dropping the torque down to that of a 1/4" thread seems to be a reasonable course of action.

Woody