A couple of things to note about torque wrenches.
First off the clicker type that you wind up the handle will go out of
calibration if not wound back to their lowest setting as soon as you are
done using them. When I worked as a line tech, I sent in each of my Snap-On
wrenches once a year for calibration.
Next is torque wrenches are terribly inaccurate at less than 20% of full
scale. So if you have a torque wrench that reads to 100 ft-lbs, and you
want to torque something to 10 Ft-lbs it will probably only be +/- 20%
accurate. Maybe worse. At above 20% of full scale the wrench might be =/-
5% or less.
Lastly you can't check a torque wrench with another torque wrench.
It takes more torque to get a fastener turning than it does to keep it
turning. This is why torque instructions always say to torque in one smooth
movement.
I used to prove this to my students in rear axle class. Torque spec on the
pinion nut was 180-200 Ft-lbs. I would have them torque the nut to 160
Ft-lbs (below spec) then reset the wrench to 200 and it would click off
without turning. It would usually take 220-230 Ft-lbs to get movement on
the nut that was torqued to 160.
Rick
On Fri, Oct 8, 2010 at 6:48 PM, Paul Osborne <paul@ece.rochester.edu> wrote:
> Well that was 3 years ago , has been used on I'm guessing 35 engines lots
> of rear axles etc and still seems to be accurate. I have cked it with my
> beam torque wrench and they both read the same.
>
> << they just replaced it with a new one from the rack.>>
>>
>> Not quite Paul, it is just indicative of the fact that the one
>> on the rack is already known to be a POS [and you'll be back<F>].
>>
>> I just got a GREAT story from my Snap-on Dealer about an hour
>> ago which I will try to relate in a couple hours <VBF> !!
>> _______________________________________________
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