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From: John De Armond
Subject: Torque Wrenches (was How to immobilize crankshaft) 
Date: Wed, 29 Jun 94 04:11:18 GMT (Peter Venetoklis) writes:

>As far as durability of beam-type wrenches, I'll agree.  However, I
>find them impractical to use, and if you don't abuse your *clicker* type
>wrench by using it as a breaker bar, hammer, etc. it is far more
>practical to use IMHO.  I also don't trust the calibration of the beam-type

Why?  As long as there is no physical damage, a beam-type wrench is
intrinsicly calibrated.  Even if you bend the beam a little, you can
re-zero the instrument and it will still be in calibration.  The 
problem with a clicker wrench is that you never know when it shifts 
calibration (and it WILL shift) unless you check it against a torque
dynomometer which uses - you guessed it - a beam.  Most folks
don't have one of those.  I personally would not trust anything to
a clicker.  My first preference is the dial-type beam wrench and the
second choice is the conventional pointer-style.

I know a thing or two about these things.  I managed the metrology 
(calibration) lab at a nuclear plant during part of its construction.
We used literally thousands of torque wrenches.  Every connection,
bolt and nut on safety-related systems were torqued, even wire 
connections.  After a horrible initial experience with clickers involving
a pretty massive amount of rework, we tossed them and bought dial 
instruments.  These were routinly calibrated.  With the exception of
obviously damaged instruments, we never once found one out of spec.
We did keep a few clickers around for jobs where nothing else would do
but we required the craft superintendent's authorization for checkout
and the thing was checked on the dyno before and after use.

The neat part about this is that it is an unusual situation where the
cheaper instrument really is better.


From: John De Armond
Subject: Re: torque wrench calibration
Date: Thu, 07 Sep 2000 07:35:19 -0400

mike wrote:
> I have an all-metal click-type torque wrench I'm kind of fond of.  I
> bought it 15-20 years ago (Utica-Bonney) and have left it sitting unused
> for at least the past five or so years.  I always turned the collar down
> to its lowest setting when I was done with it.  I now would like to start
> using it again (home use) but when I went to Sears repair to see about
> sending it out for calibration they said $50 and one month turnaround!!
> My questions are:
> 1.  Where else can I get it calibrated?  How much should I expect to pay?

You'll have to call around to find a local cal lab yourself.  That's
about right for a calibration (where the instrument is adjusted as
needed).   A check (comparison against a standard) would be a bit

> 2.  Is it usage or time which causes it to need calibration?
> 3.  If I use it before calibration is a torque wrench's tendency to torque
>     above or below the collar setting? (i.e., collar at 40 ft/lbs, will I
>     most likely get something nearer 35 or 45 ft/lbs?)
> 4.  If anyone says to just get another one what are some quality brands
>     that a non-pro mechanic would have access to?  Sears sells Digitork
>     and Microtork but I don't know anything about them.

I used to be in charge of the metrology section of a nuclear plant.
Torque wrenches used on nuclear safety systems had to be calibrated
like any other instrument.  We banned the click type wrenches
because of their absolutely sorry calibration track record.

The best instrument for the home mechanic is the old fashioned flex
beam wrench.  That's the type with a beam and a pointer that lies on
a scale.  The torque is measured by how much the beam deflects.
Once calibrated, there is nothing to go out of cal unless the
instrument is damaged or grossly overloaded.  If the pointer is on
zero when at rest and the thing isn't bent or burnt or otherwise
obviously damaged, it will be in calibration.  Best thing about the
beam-type instrument is that it is also the cheapest.

The best wrench is the beam type with a dial.  It still uses a
deflecting beam but has a dial mechanism which allows for more
precision in taking readings.  While more precise, the meter
mechanism means that it CAN go out of calibration without outward
signs of problems.  However, this is very rare unless the instrument
is used as a wheel chock or something.  I could probably count on
one hand the number of instruments we ever found to be out of cal at
the nuke plant.

I recommend you toss that click piece o' trash and get a good beam
instrument and live happily ever after :-)


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