Torque Wrench Accuracy

I'd say yes. I always use my 3/8"wrench if possible and sometimes the 1/4" wrench so I'm at the top of their range. Even then I worry about anything I'm tightening into aluminum.

 

I was aware of this, and why I bought a second wrench for things other than torquing wheel bolts. I have a second wrench for lower torque requirements.
I think it is equally important to have my wrenches checked periodically, though due to the low use they get, it has only happened a couple times over the past 25 years, but they were spot on each time (last was about 6 years ago). I use Utica Tools wrenches, and have sent them to the factory for checking. They return them with a certificate of accuracy in each direction.

 

More important than accuracy is being consistent on what you use on the threads: if the spec call for dry or lubed and if lubed what type of lube (quite often some anti-seize compound). The reason is that torque is only an indirect measurement of what is really important: axial force. The axial force varies widely even at a given, precise torque depending on the thread friction, which varies widely with lubrication and type

 

Imho - the torque is very important. If nothing else, it gives the known torque to properly hold the assembly together without damage.

Start with good tools needless to say. When I worked for an aircraft co, there were torque calibrators scattered throughout the shops. I just purchased some Snap-on tools and they were pretty much spot on over the entire range. A colleague brought in his super cheapie torque wrench an it was a random number generator for torque values. I believe most quality system call for periodic calibration intervals of 1 yr for these tools and after any event which may compromise accuracy, dropping etc..

 

I have 14 torque wrenches. I understand the range and accuracies. I have one for 40-200 inch pounds and various ones all the way up to 100-600 foot pounds. I have to have them to cover the range of fasteners I deal with. I am a big believer in proper torque. I also look it up and don't rely on my memory to get it right.

 

Per ASME B107.300 torque wrenches are accurate to +/- 4% from 20% to 100% of their rated range. They are required to hold calibration for 20,000 cycles, however most manufactures recommend less than that, from 5-10k cycles. Most places do a yearly calibration on them.

 

The director for Costco automotive was on a local BMW forum many years ago in the Seattle area and stated each Costco location has a calibration machine and they check and log each of the multiple wrenches they have at each store on a monthly basis. Anything out of spec is sent out for repair. He offered all the local BMW club members a free check once and I took him up on it. Just a check, no calibration or repairs. We just had to tell him which store we were going to, and he would call ahead and approve it. Both of my Utica wrenches were spot on...my buddy had two brand new Craftsman...both were out of tolerance...he was pissed.

 

My Snap On dealer has a torque wrench checker on his truck. I have checked mine before and had no issues.

 

I calibrate my dozen torque wrenches every year at the end of the year.

Gearwrenh 1/4 inch for small stuff up to 200 inch lbs
Snap on, Precision Instruments, and Gearwrench 3/8 for things up to 100 ft lbs. I leave the Snap on at 50 Nm, the PI one at 25 Nm, and the Gearwrench is adjustable to whatever needed
Two Snap on 1/2 torque wrenches, one set for 80 lbs, and one adjusts to whatever needed up to 250 ft lbs
One electronic Gearwrench that is used strictly for torque angle, rarely needed.
One 3/4 inch up to 600 ft lbs for the really heavy stuff.

The other Craftsman torque wrenches are tossed into the trunk of several cars for roadside emergency wheel swap duties.