Did a search for torque on the forum and found some good info but still have a question of
what the pros do. Most torque specs give two numbers Ie; 28 to 35 ft lbs. what is the rule
of thumb for the setting, HI or LO or do you add the two numbers and divide by two?
Ie; 28 + 35 = 63 / 2 = 31.5 is this the torque setting? What is the best setting?
Thanks,
Saint

 

Mahself, ah split the difference.

 

Ok,
Limits are given for a tolerable zone where the threads and or the bolt will not fatigue. Always shoot for the low limit as most will over shoot it a little by varience in torque wrench. Even if you went to the high limit and exceeded it a little there is enough safety factor to not damage the threads.

Ok now for the twist..... Some torque are given as wet or dry. This can be very important on some threads as with wet there is less galling of the threads that induce friction that increases your torque. So make sure to look and see if the manual is specifiying using loc-tite or anti-sieze as this will effect the outcome.

Ok sorry for the long wind but this gives you an idea.......

Bottom line shoot for the low limit

 

Can't speak for the pros; in Army aviation (early 70's,) they taught us to go for the middle of the range.

 

middle is where i shoot for as well, my big thing with torque wrenchs is make shure you can trust it, when i use mine i only use it for the final cpl rounds and then it goes back in the box and shelf, i dont keep it with my other tools so it does get knocked around and way off calibration

 

Don't forget, torque specs assume clean & lightly oiled threads.

 

Take the middle of the road.

 

My mechanical engineer grad motorcycle buddy has me torquing every fastener on my bike now when I do work on my bike at his home (and use his torque wrenches). I asked this very question and he explained that the low value is the minumum torque at which the fastener will not loosen; the high value is the one at which the fastener may fail/snap/strip/etc. He said, as others have said, go for the middle value. Also, most torque wrenches come with a variance stated for their accuracy, e.g. +/- 4%.

 

Split the difference.

Hack

 

Keep in mind that with torque wrenches it's less important that it be precise (within limits, of course) than it is that it be repeatable. Most of the time you care about torque it's because you have a pattern of fasteners that you want to be bearing a load evenly. If you had four fasteners holding a plate on, for example, and had to back one fastener off for some reason, you should loosten the other three and retorque them together. Even if you were sure your wrench was dead on for torque, you don't know that you had a match to the other three unless you tighten them all with the same wrench on the same day at the same temp, etc. When there's a range of values, you shoot for the middle figuring that you'll probably get over the low number and be under the high number -- after that, you only care that the torque is the same on all the fasteners.