Torque: Kicking the shot engineer

[Alan Pritchard]

Ok, let me get this straight, it appears you changed torque wrenches at step
7 (to a 4' wrench), and this is where it stopped working out??? That's how I
am interpreting your process. Torque wrenches are only accurate if they are
regularly calibrated, and even then they have a tolerance (say 10%) so your
two torque wrenches could easily be far enough out, for your maths not to
work out. If I'm misinterpreting then I apologise.
 -----Original Message-----
From: 	Robert Mangas [mailto:porter_t_dog at hotmail.com] 
Sent:	04 December 2003 15:00
To:	munrof at sympatico.ca; quattro at audifans.com
Subject:	Torque:  Kicking the shot engineer


   My name is Robert and I was a Disbeliever.  Then I ran my garage 
experiment to confirm that the extender is a torque multiplier.  At that 
point I still believed that the length of the torque wrench was irrelevant 
as long as the torque applied to the extension was held constant.

  Just for giggles, I arbitrarily changed the length of my torque wrench in 
my figuring and re-solved for the torque applied at the bolt (torque at the 
torque wrench/extender joint held constant).  It changed.  The math is 
simple.  Run the excercise and there is no arguing with the conclusion; my 
intuition let me down, and while humbling that's always instructive.

   For me, the easiest way to consider it is this:

1.  Set the applied torque as read on the torque wrench. For ease say 100 lb

ft.

2.  Set the torque wrench length.  For ease say 2'.

3.  Determine force applied to wrench.  100 lb ft/2 ft=50 lb.

4.  Determine force at nut with extender.  50 lb x 3' (2' wrench + 1' 
extender)=150 lb ft.

5.  Change length of torque wrench.  For ease say 4'.

6.  Repeat step 3; 100 lb ft/4ft=25 lb.

7.  Repeat step 4; 25 lb * 5' (4' wrench + 1' extender)=125 lb ft.

8.  Compare the results of step 7 and step 4.  Does 125 ft lb = 150 ft lb?  
It does not, therefore we must conclude that the lenght of the torque wrench

does have an effect on the torque applied to the bolt.

  Like some others have also stated, it took actually going through the math

for me to get it.

>From: "Fred Munro" <munrof at sympatico.ca>


>
>It doesn't matter whether you use a 6 inch torque wrench and 516 lbs on the
>handle or a 4 foot wrench and 64.5 lbs on the handle - if both are 
>connected
>to the 2079 tool and click at 258 ft.lb, you'll be OK.
>
>IMHO anyway.
>
>Fred Munro

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