Date: Fri, 3 Jul 1998 01:50:54 -0600
Reply-To: kenstich <kenstich@BEWELLNET.COM>
Sender: Vanagon Mailing List <Vanagon@vanagon.com>
From: kenstich <kenstich@BEWELLNET.COM>
Organization: Central Intelligence
Subject: Re: question for an engineer
Content-Type: text/plain; charset=us-ascii
Jason,
You ain't no moron -> its a fair question -> since I'm an engineer and former
mechanic - I 'll have a stab at it.
Jason Beighley wrote:
>
> I picked up a used torque wrench a couple years ago that I'd like one of you
> smart engineers to learn me about, if you can. It's rather small as these
> things go, maybe 16", reads in Nm's(up to 70) and inch-pounds(up to 600) only.
> Has a circular scale that swivels to read either of the above. It was
> manufactured by Consolidated Devices, Inc. (City of Industry, Ca). The model #
> is 6002 DI. There is what appears to be a military stock # (if you know what
> that is) of 5120-00-288-8865, and it and the date of manufacture are stamped
> one above the other on it towards the end where the socket fits on. Now, my
> ????'s are these:
There are two types of torque wrenches to my knowlege - It sounds like you
have what is called a beam-type guessing by what you describe as a circular
scale - The beam-type is based on the spring constant of the lever arm (gosh -
I hope Steven doesn't read this) versus a fixed pointer that also runs the
length of the beam. This type can not not be self-calibrated - the pointer may
be adjusted (by bending), but the spring constant is fixed by the material properties/geometry.
The "click-type" has no pointer, but is usually adjusted by rotating the
handle with respect to the beam - there is a scale on the handle indicating
the torque setting - this setting changes the preload on an internal spring
mechanism. When the indicated torque setting is reached, the the handle gives
slightly with a distinctive click. This type is more expensive, more accurate,
and can be re-callibrated (mine is a Husky - says to return it to them for
recallibration) - these frequently have ratcheting heads as well - In the
aerospace industry, we use this type exclusively to the best of my knowlege.
Further, we tag them with a calibration expiriation date.
This degree of accurracy is probably not required for most automobile
assemblies, but it doesn't hurt either - I always torque lug nuts - I used to
use an air wrench in my early days as a mechanic - When a car that I worked on
(brakes) was brought back by the owner who described seeing his RF wheel pass
his car whilst travelling down the freeway . . . I had to look him in the eye
and tell him that I was responsible - we both knew that I could have killed
him and his wife through my negligence ==>> TORQUE IS IMPORTANT !!! (exit soapbox)
One of the most critical aspects in assemblies is torque pattern and torqueing
in stages - these techniques prevent warping/sealing problems/uneven gasket
deformation. Heads/case halves and other large flanged areas are most critical
>
> Is there a way to find out if it's accurate, without paying through the nose?
> (it only cost me $10)
>
> Can foot-lbs be converted to inch lbs, and vice-versa, by simply
> multiplying/dividing by 12? I don't think they can, but I'm not sure. Can
> you splain this in moron terms so I can understand it?
Yep - Torque is force times the distance from where it is applied so:
10lb x 12 in = 120 in-lb
&
10lb x 1.0ft = 10 ftlb
which is exactly as you has guessed -> in-lb/12 = ft-lb
>
> If I can have it calibrated, will it stay that way for a considerable amount
> of time, or will I have to have it done on a regular basis?
If you have a click-type, I would have it calibrated professionally (look in
the yellow pages of the nearest city), but if you don't feel like it, or have
a beam type, try this - clamp the square socket drive lug in a vise so that
the hanging weight applied to the handle applies torque - coat hanger wire +
weights - measure the distance (torque arm) from the center of the square
socket drive to the coat hanger wire - you could use 12"of your 16" handle -
since this is 1.0ft, the hanging weight times the 1.0ft arm with various
weights would allow you to equate the applied torque to the torque reading -
although this does not change the 'setting' or calibration of the wrench
itself, it allows you to know that with an applied torque of 70ft-lbs (70 lbs
times 1ft) that your scale indicated 65 ft-lbs (or whatever it is) - so, you
could then compensate for your scale offset.
>
> I know a torque wrench is important, as are properly torqued nuts and bolts,
> but I'm too cheap to sink big bucks into a good, full-sized one if I don't
> have to.
>
> Thanks,
> Jason Beighley
> '84 GL
I started out with Craftsman tools - still use them - but as a mechanic,
really came to appreciate higher quality stuff - remember, you'll save a
bundle fixing your own stuff and quality tools last a lifetime. I just got
some Husky wrenches and a $50 1/2" click-type torque qrench at Home Depot two
months ago - its not Snap-on, but the wrenches seem really good
(feel/balance/finish) and the torque wrench is a pleasure to use (I've had a
Craftsman beam-type for years).
The aerospace industry has torque tolerances - indicated either on the
drawings or in production standards, but I've not seen this in any auto repair
manuals - I would imagine that the professional organizations (ASME/SAE),
particularly ASE have some tolerance standards.
Regards,
Ken Stich
