Accuracy of torque wrenches?

[chunderlicious]

Calm down. I'm not suggesting you're wrong. I couldn't understand what you were trying to say. I'm starting to understand now.

not getting worked up, just flustered about thinking of the right wording to explain it..... im just a simple diesel fitter

[WRXZook]

Calm down. I'm not suggesting you're wrong. I couldn't understand what you were trying to say. I'm starting to understand now.

not getting worked up, just flustered about thinking of the right wording to explain it..... im just a simple diesel fitter

You might be under too much tension to think straight.

[-Scott-]

Calm down. I'm not suggesting you're wrong. I couldn't understand what you were trying to say. I'm starting to understand now.

not getting worked up, just flustered about thinking of the right wording to explain it..... im just a simple diesel fitter

You might be under too much tension to think straight.

Stop winding him up.

[WRXZook]

Calm down. I'm not suggesting you're wrong. I couldn't understand what you were trying to say. I'm starting to understand now.

not getting worked up, just flustered about thinking of the right wording to explain it..... im just a simple diesel fitter

You might be under too much tension to think straight.

Stop winding him up.

He is a diesel fitter, he can take bit of a knock.

[date]

I have tried 4 times to draft a reply to this question, but have decided each time that it is too complicated to adequately explain. Suffice to say that although a tension wtench may be accurate to within 5% (or whatever), the thread surfaces you are tightening will vary in the roughness considerably more. Add to that the roughness of the surface under the rotating bolt head and you have a potential for enormous variation in roughness (hence friction in the bolting system). Then, do you have lubrication on the thread surfaces? If so, what is the coefficient of friction and how does it vary from the original designer's assumptions? Probably at least 70% of the torque in tightening a bolt on a nut goes into friction - teh rest goes into putting tension in the bolt and this is what you are really trying to get. All up, you have a mix for an accuracy of gettiing the required bolt tension of at least 25%.

Using a torque wrench is the simplest way of getting at least some reliable tension into a bolting system. Assuming that you have lubricated all the bolts to the same extent and you are using identical bolts and nuts, it also helps in getting at least something close to even tension on all the bolts in that system. Even if it isn't the tension that original designer wanted.

To send a torque wrench away for recalibration is really a waste of money unless it has been grossly abused.

If you wanted a really accurate tightening system, you have to measyre teh actual extension of the bolt. This is done for critical applications, but for general purposes, the good old tension wrench gives us at lesat some indication of teh fact that teh bolt has been tightened to a reasonable level.

[ledgend80]

To send a torque wrench away for recalibration is really a waste of money unless it has been grossly abused.

this maybe somewhat true but what about the companies that need it done for the quality assurancy procedures. and what do you call grossly abused?

[date]

Date wrote:
"To send a torque wrench away for recalibration is really a waste of money unless it has been grossly abused."

Legend80 replied:
"this maybe somewhat true but what about the companies that need it done for the quality assurancy procedures. and what do you call grossly abused?"

Quality Assurance procedures probably require calibration checks of the equipment, but I would hope that the QA procedures also probed deeply into the actual work practices - the procedures used to tighten bolts as well as the equipment used. Like a lot of the QA procedures, the paperwork is mostly there to find someone to blame when something goes wrong. Still, we have to live with them. My comments about waste of money really refers to the home handyman who is fixing up his 4x4, but probably apply equally well to companies using QA procedures. At least with QA, the bolts will probably get torqued up to a given torque, whereas without it they may be missed out or simply flogged up until the spanner rings.