REALLY Basic Torque Question

[c23380]

I guess I stated it wrong. IF he feels it changes with a 6in or 12in or just a socket on the torque wrench, then ad a couple. If not ok. We started out torquing a tractor lug nut. To me we are arguing over something so small it really does not matter.

 

[patrick_g]

Although this might not stir up the heated controversy of a magic conveyor belt and an airplane....

Here is the challenge:

Anyone who believes adding (standard not torque limiting) extensions to a torque wrench changes the results, please supply any credible reference to support your contention and I will enter your name into a drawing where you may win a swell prize.

Gut feelings, third party hearsay, and such as I thought I remember something about... and similar are not qualifying! A reasoned logical argument based on accepted principles of physics may be substituted for credible references.

SPYDERLK You qualify for 10 bonus points for detailing the basic truth as regards the torque issue and why extensions DO NOT make a change in the results. I couldn't have wished for a more cogent explanation nor have supplied it myself.

Now to await the reasoned response from the other side of the issue...

Pat

 

[Redneck in training]

I do not know which side of the argument is right but my guts feeling is that extension makes some though negligible difference due to torque applied dynamically. Here is an experiment I would propose. Take two clickers and connect them someway together by a short connection. Then adjust the setting such a way that both click when force is applied. Then put a long extension in between and apply a force. I have only one clicker otherwise I would try it.

 

[mwb]

I do not know which side of the argument is right but my guts feeling is that extension makes some though negligible difference due to torque applied dynamically. Here is an experiment I would propose. Take two clickers and connect them someway together by a short connection. Then adjust the setting such a way that both click when force is applied. Then put a long extension in between and apply a force. I have only one clicker otherwise I would try it.

Here you go; I am the technical manager of a calibration lab. We do thousands of torque wrenches a year, all brands and types (beam, click, dial, electronic).

Comparing any of the above wrench types to a Norbar torque transducer (0.1% IV) with no extension (wrench directly engaged to the transducer) and with a 12" extension produces NO difference in recorded value from the Norbar analyser (peak function). There is greater uncertainty from the repeatability of the wrench itself. This is a static test (i.e calibration of the wrench), there is no nut or threads involved and only the deflection of the strain gage transducer.

IMO, the designer (engineer) for the engine or whatever would have specified the correct torque to be used with consideration for all of the concerns listed (lubrication, bolt stretch, fastener type...) and to try to re-engineer this at the workbench is probably not worth the time and trouble - and could also cause problems (miscalculation).

If you are worrying about adding / subtracting 2% for whatever reason then you might want to purchase something better than a 2 or 3% wrench. Also, unless you are loading the wrench using a load fixture (torque calibrator with worm gear ) most competent users will still slightly exceed the click point when pulling by hand. When pulling by hand the torque calibrator will on average record higher values than when using a mechanical device (it's hard to release the wrench exactly on the click).

 

[SPYDERLK]

When i was a boy my father, who stopped just short of a PhD in Physics, told me offhandedly while doing mechanical work that a long screwdriver could tighten a screw better because it gave more leverage. I was intuitively skeptical of this but didnt say anything for awhile. When I did, it took him no time to come to the realization. ... It seems that any af us will sometimes adopt and pass along a plausible "truism" without really thinking about it. Its easy to see how it could go on in this case if no skepticism were applied. -- Long means bigger handle and blade, thus better purchase on each end for turning. Also less sensitivity to lateral offset of the driven axis. Performance shows a seeming validation, however skirting the Physics.
larry

 

[merrickvilleguy]

The problem with that is that has nothing to do with torque ... the torque remains the same regardless of the length of the handle so long as the handle is perpendicular to the plain the force is being applied in.

Heck the handle could be 20' long and so long as it was the same diameter as a short one, you would apply the same torque with the same force (assuming the handle didn't just twist)

 

[merrickvilleguy]

Although this might not stir up the heated controversy of a magic conveyor belt and an airplane....

That one always ticked me off ... most people only have experience with cars (wheels apply force to the ground) so the idea that the wheels on a plane don't propel it at all (less friction in the bearings but i digress) led to many an argument prior to that mythbusters episode

 

[BeeferMan]

Hey, this thread seems to be quieting down a little... let's see if I can stir it up some.

If the length of an extension makes a difference in the torque applied at the far end, then the diameter of the extension must also make a difference...

Have at it...

 

[c23380]

I would be more interested in the magic carpet airplane thing. I fly, work on em and build-em from scratch. Someone tell me about the myth we are joking about, please. Thanks, Mike

 

[SPYDERLK]

Hey, this thread seems to be quieting down a little... let's see if I can stir it up some.

If the length of an extension makes a difference in the torque applied at the far end, then the diameter of the extension must also make a difference...

Have at it...

diameter would make a difference only when the smaller of the two could not maintain a straight drive axis. This condition would be pretty obvious as it became a pretzel.
larry