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Old April 24th 17, 02:06 AM posted to rec.bicycles.tech
John B Slocomb
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Posts: 333
Default torque wrench issues

On Sun, 23 Apr 2017 22:06:05 +0100, "Benderthe.evilrobot"
wrote:


"Emanuel Berg" wrote in message
...
I finally got the 1/2" torque wrench,
28-210 Nm, not even made in China, but in
Taiwan! Eh... I guess it depends who you ask if
that is China or not

It has a locking screw, a torque setting
handle, a scale (Nm as well as "FT-LB", some
English unit I take it?) - it also as a
locking lever on top just like an ordinary
ratchet, so it can go both ways, clockwise and
anti-clockwise.

The torques only work in the
clockwise direction. So if the
locking (ratchet) lever is set the other way,
it is just a ratchet, right? Well, in
the manual it says:

Note: Never use the torque wrench to undo
nuts, bolts or other fasteners as this will
damage the ratchet mechanism and the
calibrated settings.

So how does that add up? Is it only OK to use
the anti-clockwise pull to insert things, which
would require a left thread? (And it would be
just a long shaft, with the torque not
in effect.)

As for me, I don't plan using it for anything
but as a torque, because I have other, less
expensive ratchets and spanners to do the
everyday stuff. But of course, I'd like to know
what it means.

It also came with a certificate with data on
the calibration and in the manual it says it
should be recalibrated at least every
12 months.


Calibration is irrelevant if you don't follow the rules to the letter.

Most torque settings I've seen were for dry threads - any stray lubricant
and you might even twist the end off at the correct torque.


Tightening fasteners is a far more complex matter then just putting a
wrench on them and turning them.

For heavily loaded fasteners Caterpillar recommends (1) clean the
fastener, (2) lubricate the fastener (3) torque to specification in
three steps, i.e. first torque all of the fasteners to 40% torque,
then to 70% torque and then to final torque.

I worked on a radial aircraft engine that required the bolts that held
the three piece crankshaft together be tightened to a specific bolt
stretch. No torque specified. Measure the length of the bolt and then
tighten it until it stretched the required amount.

A White Superior stationary engine had a special "bolt jack"to tighten
head bolts. A small hydraulic jack like device. You put the nut on the
bolt and then installed the jack. Then jack the bolt to a specified
pressure on the hydraulic gauge and then tightened the nut finger
tight and remove the jack.
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