Torque wrench question

[dnschmidt]

All a torque wrench really does is ensure a fastener to be reasonably tight. If you want the real deal then you've got to go to torque angle. With torque angle you know the pitch of the screw, you know how many degrees you're tightening it and therefore you know how much you've stretched the bolt which is the only thing that matters anyway. Torque Nazis assume that this measurement does more than it actually does. It is a very flawed and indirect method of determining bolt stretch.

 

[guy48065]

The internal release of a clicker happens momentarily before the click. By the time you hear/feel the click your torque has already dropped off 10-20%. You lack skill (to be kind) if you continue to pull past the click because the click is caused by the internal taper behind the ratchet head coming into contact with the tube wall. Solid contact. At that point the torque will rapidly start to climb again. BUT IT TAKES QUITE A LOT OF ADDITIONAL MOVEMENT TO CLIMB BACK UP TO THE RELEASE POINT, AND THEN TO EXCEED IT.

When a clicker is calibrated the indicator (usually a peak-capturing digital readout) catches only the highest torque applied. The operator never continues to apply force beyond the obvious and visible fall-off. That peak is incredibly repeatable for such a simple mechanical device. Trust it. For best, most accurate results using a click-type torque wrench you need to apply force the same way the wrench is calibrated--slow & steady.

 

[guy48065]

...It is a very flawed and indirect method of determining bolt stretch.

It IS indirect but certainly not flawed. It's just a comparison measurement. The torque tells little about the clamp force applied but once the "correct" value is determined it's possible for everyone else to repeat--without needing ultrasonics, micrometers, etc.

 

[gdocktor3]

This has become unnecessarily waaaayyyy too complicated. Unless you're working for NASA, set the wrench to the desired torque setting and use it. Once it clicks, you're done.

 

[guy48065]

Snap On did research that led to the patent for their digital Techwrenches' "early warning system". Basically, the research showed that the inertia of that last pull resulted in over torque if we pulled into and even slightly through the click and into the release. The early warning buzzer is triggered 5% below the target. That's roughly the amount Snap on found we were over torqueing.

BUT IT TAKES QUITE A LOT OF ADDITIONAL MOVEMENT TO CLIMB BACK UP TO THE RELEASE POINT, AND THEN TO EXCEED IT.

This is the one thing I don't like about electronic torque wrenches. They are unforgiving. They do NOT release force once they beep and will continue to over-tighten until something breaks.

I can't lay my hands on a Tech2 manual at the moment but if memory serves that "5%" early warning is user-adjustable--which can also cause problems. Last one I checked beeped at 98FP for a setting of 100. At 100 it changed to rapid beeping. So I could be argumentative and claim that a SnapOn Techwrench doesn't tell you exactly when you hit the target--it warns you ahead and again when you are passing it by ;-)

 

[guy48065]

Even more you probably don't need to know:

At a setting of 100 ft-lbs:

SnapOn Tech2:
98 - short beep/handle buzz.
100 - rapid beeping/continuous buzz

CDI Computorq:
90 - yellow light
96 - green light/tone
100.1 - green light/beeping
104 - red light/rapid beeping

Jetco ED-250I:
85 - yellow light
99 - green light/beep
101 - red continuous light/rapid beeping

Gear Wrench:
80.1 - yellow light
96.1 - red light/tone
105.1 - red flashing light/tone


Point is: THEY'RE ALL DIFFERENT.

 

[ez-duzit]

This has become unnecessarily waaaayyyy too complicated. Unless you're working for NASA, set the wrench to the desired torque setting and use it. Once it clicks, you're done.

This.

 

[mbret2004]

How does one learn to use a torque wrench by owning one? I guess that's my point. If you learn to aim your rifle by reading a book, you may or may not hit the target when you get to the range. But either way, you'll know. With a torque wrench, theres no practical way to know if you are using it correctly or not. All you can do is rely on the training most of us don't have.

Using a torque wrench isn't complicated science, nuclear engineering comes to mind as a complicated science.

Sometimes with a t-wrench you have to compute torque because of the angle of the fastener is difficult to access. That's grammar school math. Otherwise, it's palm wrapped around the handle, slow steady pull until the wrench breaks away. You don't do the "hot rod tv show" thing where they click the wrench numerous times AFTER the initial break away. Also, you need to cycle the wrench three times or so at its lowest usable setting BEFORE using the wrench. I won't go into any more detail here because you already know everything. I worked on aircraft for 40-years and wouldn't be up to your level of knowledge on the subject.

 

[gdocktor3]

Unless a fastener's recommended torque setting is 5 ft lbs less than its failure/breaking point, how the heck are you breaking bolts by going a little over? Seriously, if you can't tell when too much is too much, you shouldn't be using any torque wrench. Electric, beam or clicker. It's not the tool, it's the user. I installed something with cheap hardware once that was supposed to be torqued to X ft lbs. It didn't click and got to a point where I new something wasn't right, so I disassembled. I found the lock washers had flattened out and were mangled and being squished into the nut. If I had kept going until it clicked, yes the bolts would have broke, but I new better. I guess that is something you can learn only through experience though...

 

[Adam.C]

This is the one thing I don't like about electronic torque wrenches. They are unforgiving. They do NOT release force once they beep and will continue to over-tighten until something breaks.
)

Right. No release with digitals. But they record the max applied installation torque. And flash red if you go over. Some record/remember the actuals.

 

[T45]

Thanks for that write up Adam, got me thinking about stuff I never thought about before.

So what's the overall opinion on the "double click" technique I've heard and seen people use? Tighten until it clicks, then give it one more click. I would assume that's just over torquing?

At the risk of keeping this thread alive

a two-stage technique is basically to stop at 80% and then go from 80 to 100% in a single, un-interupted motion.

There are reason why this is, in critical applications, technically proper technique, but nobdy here seems to care .

Just follow directions for the parts youa re working on, and if they say to go in stages, you go in stages.

Keep in mind some th the thread are not about snobbery or expensive tools, they are basic concepts like repeatability vs accuracy...and using indirect measurement techniques to esitimate altogether different variables.

The reason people riff on about 'skill' being relevant is because of all the embedded assumptions that go with the aforementioned concepts. In some circumstances, it helps to know tha the thing you are working on is textbook conditions, or not. And if not how to adjust.

To use an anology, in target shooting everyone knows how to aim using crosshairs. But in real world work you need to take into account the variables that are not per the simple example. You need to tweak your aim a bit for wind speed, direction, aerodynamics of your match ammo, and all that good stuff. You can either adjust the crosshairs or aim a little bit away to a point that compensates for the other variables. They call that 'adding dope', its a casual nickname but its not hocus pocus it all comes back to basic science of ballistics/trajectory etc.

But rarely to you ever just aim for the crosshair without any dope/correction. That would asssume you already did a bunch of homework and that the conditions were exactly as your assumptions, which might of course be true but is either luck or some good skill guessing.

But nevertheless, nobody ever got far without learning how things deviate from the classical assumtions and making certain adjustments.

Whether or not it pays to be oblivious to this kind of stuff with torque really comes down to how good the engineers were in making sure the parts are overbuilt to withstand various of care (or carelessness).

 

[Bcom]

Did i mention that mine fell apart since i was using it as a back scratcher and a shoe horn? I guess this isnt the correct method. Heck i could also use it as a back brush in the shower and a toothbrush. One can only be so lucky to have such a versatile tool.