my take on torque

[SJ]

I like these questions. Every once in a while, we need to re examine what
the hell the topic is.

SJ
85 Dodge PU, D-250, 318, auto
85 Audi 4k - - sold but still on the road
88 Audi 5kq
90 Audi 100q


> From: <auditude at cox.net>
> Subject: my take on torque
>
> While half-following the thread on torque and all the answers offered, at
one point I forgot what the question was.  But I think the question is how
much torque is actually applied to the crank bolt when following the manual
using the recommended tools and technique.
**** Correct. What is the bolt torque . . .for those that do not have tool
2079, but have a big torque wrench.
>
> I'm not familiar with the math involved in calculating the resultant
torque at the bolt using the tool, which probably has a known length.  But
is the math formula being disputed?  Is there more than one being offered?
*****Nope, the formula is correct. But the answers were puzzling.
>
> To me it seems intuitive to think that any torque wrench of any length is
intended to produce the same torque at the bolt when used as intended.
**** Correct . .so far. hehehehe
>
> I do believe the factory tool is a torque multiplier, as well as a way to
get to the bolt without pulling too much off the front of the car.
**** Correct on both counts. Except the second reason was the primary reason
for making the tool. The force multiplication is a side effect.
>
> I don't know enough about this stuff to be able to say whether putting a
pipe or extension on the handle end of a torque wrench will affect it's
accuracy.  I am temped to say that it will, since I believe you are not
supposed to touch the wrench anywhere but the handle.  If I put my hand in
the middle of the torque wrench opposite the direction of force, for example
if I was pulling up on the handle, I imagine the hand in the middle of the
wrench would reduce the amount of "handle" force getting to the bolt.
**** This point is really irrelevant to the subject. Someone brought it up
as a "what if" scenario. Lets just say that you have to be nuts to use a
pipe on a torque wrench. If you cant exert enough force on a torque wrench
to make it click on a setting within the wrench range, then you are either
crippled or a wussy.
Wrench designers make a wrench longer if force becomes an issue.
>
> I believe the above is only relevant because were are talking about
improperly using the torque wrench.  I think the discussion about torque
wrench length is totally pointless.  If you use a 2 foot torque wrench
properly or use a 2 mile torque wrench properly, the resulting torque at the
bolt is the same.
**** Ahhhh . .now you are getting to the meat of the topic. Yes, discussion
of torque wrench length is totally pointless . . . .. when you are
discussing normal usage. However, when you are using an extension such as
tool 2079, then the wrench length is the key point. The wrench length is
used in the formula for calculating the bolt torque, and it makes
significant differences in the results.
>
> So in summary, I think the torque applied by any correctly used torque
wrench is measured at the socket.  So the question becomes, what is the
torque at the bolt when the stupid factory tool is used?
****Yeppers. This is the $64,000 question. This is what we are trying to
figure out. Give the man a ceeegar!!!
>
> I'm sure I don't understand the rest of it (and maybe the part above!),
because there has got to be something more for there to be such a long
thread.  I suspect adding length from the socket end of the torque wrench is
not the same as adding length to the torque wrench itself.  (by that I mean
using a longer torque wrench, which wouldn't change the applied torque, but
would require less force on the handle end, and more distance)
****Your muddled comment here is what the long thread is all about. Most of
us are muddled, including me. But, I think I have unmuddled myself . . I
think.
Changing the extender length at the socket, and/or changing the torque
wrench length(not by adding a pipe, but using a longer wrench) affects the
resultant torque at the bolt.
>
> It's possible that a simple formula for extending the lever could be used
to calculate torque.  But, my hunch is that since the "click" occurs in "the
middle" of the combined torque wrench/factory tool, instead of near the
bolt, there there is another factor to consider.
**** Nope. Its all a simple force times distance problem. The extender
complicates things, but not by much.
>
> The one analogy about the four corners of the torque wrench, pushing in
four directions, seems to make a little sense.  I don't know what happens
with the "extra" three directions of force, but the only direction that the
torque wrench can go is the direction the crank bolt is turning.  So, the
torque wrench is pushing the factory tool clockwise with a certain amount of
force.  If that force is multiplied by the factory tool due to its length,
then it should be calculable.
****Yup. Excursions into the "4 corners", and sines and cosines only muddy
up the waters.
>
> Hmmm.  So if the "click" point of the torque wrench is not at the same
point as the center of the bolt being tightened (it's in between that point
and the handle), then at that point it is not measuring the "twist" that's
occuring at the bolt, but the force applied in a single direction at the
click point.
**** "Click point" is irrelevant. Its just another excursion into muddy
waters. Replace the click wrench with a beam balance wrench. Now you have no
"click point" to worry about.
>
> So, by using the factory tool you are moving the click point further away
from the axis of the bolt than it already is.
****Now you see why the thread gets long. hehehehehe
>
> My conclusion is that the formula for calculating the effect of lever
length on torque should be applicable to this problem.
**** Yes, the formula is applicable.

>In other words, adding length to either side of the click point should have
the same effect, since it is >measuring force in a single direction, and not
the "twist" dimension (directly).
> Make sense?  Or just more talking out of asses? :P
****Not much. Hehehehe    See! Its easy to get off the track and
overcomplicate things.
>
> I also believe that getting it as tight as possible with whatever you can
manage is probably fine as long as you have some grunt.
**** I suppose so, depends on who is doing the grunting and what you think
"tight as possible" means.

****This thread is a pleasant diversion for the technoheads and the
engineers in the audience. This has the same satisfaction for me as knitting
has for my wife.

Here is an exercise that demonstrates what we are talking about.

A------------B-----------------------------C
A-B is 1 foot
B-C is 2 feet
A-C is a piece of wood with holes drilled at points A, B, C

Put a screw at point B and screw the wood to a barn door. Put a washer
between the wood and the door so we dont introduce any friction between the
2 surfaces. Tighten the screw so the wood will not rotate.

We want a torque at point B of 258 ft lbs. How much weight to hang at point
C?
Easy, T=FD . . 258/2 . . 128 lb weight hanging at point C

Now put in a scew at point A, make it real tight. Remove the screw at point
B. What is the torque at point A?
Easy, T=FD . . . 128 lbs X 3 feet = 384 ft lbs

See! The problem is simple. Simple when you know all the details.

Now try this out.
A-B is 1 foot
B-C is unkown . . but its most likely between 1 foot and 4 foot
Torque at point B is 258 ft lbs

What is the torque at point A? Point A of course is the bolt torque.
Multiple answers are not acceptable.

You have 8 hours to complete this homework assignment. Failure is not an
option.
Drinking beer while you work is optional.


SJ