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  #81  
Old 02-14-2012, 03:09 PM
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marchudson marchudson is offline
 
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Larry

You are correct. Using your example, at 12" the applied force required is 64lbs. The three inch extension will experience 80 FT-LBS of torque. Your math example assumes a torque wrench that is calibrated at 12 inches.

The problem arrises when Tim (380mxc) has a torque wrench that calibrated at 22.57 inches.

Torque = force X distance

For a 12" torque wrench with a 3" extension, setting 64 FT-LBS results in 80 FT-LBS at the bolt. 64LBS x 1.25feet = 80 FT-LBS

For the 22.57" torque wrench with a 3" extension, setting 70.56 FT-LBS results in 80 FT-LBS at the bolt.

A force of 37.23LBS at 22.57 inches (1.88feet) = a torque of 70.56 FT-LBS
Adding a 3" extension to the equation. 37.23LBS x 25.57 inches (2.13feet) = 80 FT-LBS

Tim can't just multiply torque required by .8 and plug that into his torque wrench. His torque wrench manual values line up with the extension formula.

Wrench torque = Torque Spec * (Wrench length / (Wrench length + extension length))
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  #82  
Old 02-14-2012, 03:41 PM
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Garage Guy Garage Guy is offline
 
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Mike,

Quote:
Adding the extension changes the location of the center point of rotation
With the extension, now there are two center points of rotation, one at the torque wrench head, the other at the nut. This whole discussion is about the multiplier that relates the torques applied around these two axes.

Quote:
and the head on the torque wrench is now moving in an arc, not rotation.
Well if we're measuring static torque, nothing is moving at all, but you are getting at a key point. The head on the torque wrench has both a torque moment around the head axis, and is applying a force perpendicular to the extension wrench arm. The torque wrench is directly measuring the first of these (that's what torque wrenches do) and is not measuring the second one directly at all. (But you can compute the second one if you know the torque wrench and extension wrench lengths.) I think a big part of the confusion is folks confusing the two.

--Paul
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  #83  
Old 02-14-2012, 04:10 PM
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Now what was for sale?
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  #84  
Old 02-14-2012, 04:22 PM
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Originally Posted by sstellarv10 View Post
Now what was for sale?
One each, brain, thoroughly used up.
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  #85  
Old 02-14-2012, 04:23 PM
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In the video the wrench appears to be made of 2 thinner pieces based on the appearance. is it? Or is it one piece with a line around it? Thanks Marty
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  #86  
Old 02-14-2012, 04:26 PM
nauga nauga is offline
 
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This is supposed to be a prop wrench, how 'bout a prop service bulletin for reference?

http://www.mccauley.textron.com/sb227B.pdf, see the last page.
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  #87  
Old 02-14-2012, 05:23 PM
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Quote:
Originally Posted by nauga View Post
This is supposed to be a prop wrench, how 'bout a prop service bulletin for reference?

http://www.mccauley.textron.com/sb227B.pdf, see the last page.
To save everyone the trouble of an extra click, the McCauley Service Bulletin above says that when using a torque wrench with an extension:

dial reading = torque wrench length (ft) x desired torque (ft lbs) / [torque wrench length + extension length (ft)]


Clearly this falls into "the 0.8 multiplier is not a constant" camp. Im back to not knowing what to think. Could this SB really be wrong?

erich
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  #88  
Old 02-14-2012, 06:42 PM
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Quote:
Originally Posted by erich weaver View Post
To save everyone the trouble of an extra click, the McCauley Service Bulletin above says that when using a torque wrench with an extension:

dial reading = torque wrench length (ft) x desired torque (ft lbs) / [torque wrench length + extension length (ft)]


Clearly this falls into "the 0.8 multiplier is not a constant" camp. Im back to not knowing what to think. Could this SB really be wrong?

erich
OMG... this is the same thing that AC 43-13 says, could it actually be that all these documents have been wrong all these years and remarkably the brilliant minds on VAF have finally discovered the truth

As I said before, show me the math and I'll be a believer, but I still haven't seen it.

All ft pound wrenches are not 1 ft long which is what this "theory" is based on. If every torque wrench was 1 ft long then Allen would be right, end of story.
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  #89  
Old 02-14-2012, 06:55 PM
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Allan,

Looks like the Retail Price of your wrench has gone up... include a 12" 3/8" drive Snap On high quality torque wrench in the wrench kit and then nobody will have the need to do the math.
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  #90  
Old 02-14-2012, 07:30 PM
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Take 3 torque wrenchs, one 1 ft long one 2 ft long and ine 3 ft long. All are calibrated for 100 ft lbs torque.
So even though they are different lengths, they all put exactly the same 100 ft lbs of torque at the head.
So all three torque wrenches put exactly 100 ft lbs of torque at the head and then you add the exact same 3 " extension to them. Wouldnt the 3 " extension have the same effect on the 100 ft lbs of torque at the head on all of them?

Just saying...
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