Torque calculation for extensions on a Torque wrench

[JCyrbok]

With out getting into the mathmatical specifics for my question I need to know when using a Torque wrench with a Crowsfoot type extension, the setting for the wrench ( clicker type) would be LOWER then the torque required for the fastener.



IE: If I need to torque to 18lbs/ft I would set the wrench for 16. 5 lbs/ft, Which with my Crowsfoot extension and the calculations I did gives an actual Torque of 17. 92 lbs/ft.



Sound right? With extension u set the wrench lower to achieve the higher setting due to the now longer lever? Clear as Mud?



I followed the calculations in the Craftsman manual with the wrench so I think that the numbers are right, but just checking the "theory" part of it.



Thanks

J-

 

[snowracer69]

I'm curious as to what is considered a "crows foot" extension... .



By the theory (remember, it's just theory, but almost always with something this simple it should hold true) I've learned in my enginerding classes, torque should be translated 100% through an extension... hence why I'm asking what exactly is a "crows foot" extension.



Josh

 

[Joe G.]

A crows foot is like an open end wrench that had been cut off close to the business end. The little stub has a square hole in it for the ratchet. The idea is to be able to turn hex head fasteners if you can't get a normal socket on it.

 

[snowracer69]

Ok, that's what I was thinking they were...



so, with that extension being offset from the end of the socket extension you're going to end up with a larger torque out on the end of the crowsfoot due to the small distance from the extension to the crowsfoot... .



Anybody else confused after reading that sentence?



Josh

 

[Diesel Freak]

If the crows foot is 90 degrees from the end of the wrench, the no correction is needed. (forms an 'L' with the TQ wrench)



If the crows foot is inline with the TQ wrench, then a correction is needed... and indicated TQ will be lower than applied TQ as you previously stated.



T= applied TQ

L= TQ Wrench Lever Leingth

A= Adapter extention leingth

R= Indicated TQ Reading





R= (TL)/(L+A)

 

[illflem]

Originally posted by snowracer69





Anybody else confused after reading that sentence?



Josh

Not confused but never heard them called an extension before, just a plain old crows foot.

 

[JCyrbok]

Thanks

Thanks guys. It looks like I'm not too dumb after all! LOL



I came up with a torque setting of 16. 5 for the wrench with a length of 13" and exstention of 1. 125" to acheive 17. 92lb/ft. I figure i'll get it to click and then give it just a small nudge more for the 18lb/ft. SOund right?



Sorry, did nt mean to throw everyone off with the "crowsfeet" I figured that if I called them an extension that it may be easier to understand.



Thanks again, now to tackle my first LP change on Sunday!



J-

 

[Steve Campbell]

Can you take that same "set-up"....

and try it on a bolt you were able to torque normally and see if your "theory" holds true?

 

[rbattelle]

Remember to measure your extension length from the center of the torque wrench square-drive to the center of the bolt you're turning when the crows foot is fully installed on the bolt!



BTW, I would question whether your torque wrench is even accurate to make doing the calculation worthwhile!

 

[JCyrbok]

Well did the calculations, torqued a bolt to 18ft/lbs and then torqued it with the crowsfoot and calculated TQ setting and all was fine. They clicked at the same time, close enough I figure, I didnt strip the threads out of the aluminum and there is no leaks so I guess it worked.



Thanks for all the input,



J-