Re: WHAT A BOLT IS, AND HOW IT WORKS

"TeGGeR®" <tegger@xxxxxxxxxx> wrote
> "Elle" <honda.lioness@xxxxxxxxxxxxxxxxxxxx> wrote
> > "TeGGeR®" <tegger@xxxxxxxxxx> wrote
> >> Each wheel has, of course, 4 nuts. Each lug nut was tightened by me
> >> to 75 ft lbs back in the summer. Well, I just measured the torque
> >> necessary to break them loose just now, in two pound increments on
> >> the click-wrench.
> >>
> >> Guess what? Each one required about 90 lbs to crack free.
> >
> > For the archives, I think it's important to note that the torque
> > wrenches accessible to the ordinary consumer are not supposed to be
> > used to measure loosening torque.
>
>
>
> It's not supposed to be used to measure loosening torque because of the
> possibility of overloading the mechanism.

> 90 ft lbs is well within my
> wrench's maximum of 150 lbs.
>
> I started at 75, and worked my way up in 2 lb increments.
>
> There is no harm done to a torque wrench used in such a manner.

I don't agree. Using a torque wrench as you describe puts a lot more wear
and tear on it for each assessment of a bolt's loosening torque (as opposed
to the one-time application of tightening torque). The wrench "allows" only
so many clicks before calibration becomes a concern.

Without good calibration, the torque wrench is useless.

> An update to yesterday: I picked up a nail in one tire two weeks ago. I
> brought it to a tire place to get the puncture repaired, and watched while
> the tire guy used a torque wrench to tighten the lug nuts. I noticed /all/
> the tire guys were using torque wrenches as a matter of course.
>
> By the pressure he appeared to be applying, I'd /guess/ the force used was
> on the order of 100 lbs before the wrench clicked. I did not ask to see
> what the setting was.
>
> When I tried to undo the nust on that particular wheel yesterday, I
reached
> 100 lbs with the torque wrench, with no apparent movement visible at the
> nuts. I then laid aside the torque wrench, for fear of the very damage you
> mention.
>
> I enmded up having to STAND on an extended wrench, and bounce up and down
> on it! I weigh 180 lbs, so I must have been applying removal torque of
over
> 200 lbs before nuts came loose.
>
> I'm wondering if removal torque increases exponentially compared to
> tightening torque once you get closer to maximum tension.

Off the top of my head, I would say the removal torque probably varies more
at higher axial loads than lower axial loads. That is, if one takes several
measurements of loosening torque at a given lower axial load, this
collection of "low load removal torques" will have a lower standard
deviation than that of a corresponding collection of "high load removal
torques."

The thread mating surfaces are closer together at higher axial loads. So
static (as opposed to dynamic) friction effects should prevail increasingly
more the closer one gets to the maximum allowable axial load in the bolt. In
addition, surface conditions can vary a lot due to wear, how lubricant was
applied, temperature, even the manner in which the bolt was tightened. The
variability of surface conditions from one tightening to the next should
increase the unpredictability of loosening torque at higher axial loads.

By contrast, at lower loads, the thread mating surfaces are farther apart,
so the mating surfaces' condition should have less of an effect on the
friction between them. Below a certain axial load, it's more likely to be,
say, oil molecules sliding over oil molecules. Whereas at higher loads, one
can't say with as much certainty whether it's oil sliding over oil or steel
sliding over steel, with imperfections in the steel and wear in the threads
at work as well.

Otherwise, if your car were just for lab experiments, I would be tempted to
repeat the experiment with a torque wrench of reasonably-well known
calibration. This sounds fishy, like those guys are abusing their highly
sensitive torque wrenches, to me.

Regardless, yours is a good example of why folks should probably do their
own torquing of their lug nuts, even after they've been torqued at the shop.


.

Relevant Pages

  • Re: WHAT A BOLT IS, AND HOW IT WORKS
    ... I just measured the torque ... Each one required about 90 lbs to crack free. ... There is no harm done to a torque wrench used in such a manner. ... the tire guy used a torque wrench to tighten the lug nuts. ...
    (rec.autos.makers.honda)
  • Re: Shimano freehub body removal
    ... I have torque wrenches, but don't think I've ever used ... "torque wrench" to every question is foolish. ... worry about over tightening and hence use a torque ... For stem clamps with two or four bolts it's ...
    (rec.bicycles.tech)
  • Re: Shimano freehub body removal
    ... I have torque wrenches, but don't think I've ever used ... "torque wrench" to every question is foolish. ... than when tightening the bolts that hold ... worry about over tightening and hence use a torque ...
    (rec.bicycles.tech)
  • Re: Torque wrench question
    ... criticality of accurate torque is less than I assume but the fact remains ... a torque wrench is going to be by far the most accurate way of doing ... > Six methods can be used to control tightness of a threaded fastener. ... > How much to turn the nut or bolt cannot be calculated (because of the ...
    (rec.bicycles.tech)
  • Re: Shear strength of 3/4" square steel?
    ... I've been using a torque multiplier but for some of the bolts there's ... My big torque wrench has lost the 3/4" square shaft which connects it ... If I square up a piece of mild steel bar, will it take the 500 lb-ft ... 3/8" 100 ft lbs ...
    (uk.rec.models.engineering)