REALLY Basic Torque Question

[Famah]

Greetings Learned Forum:

I need to torque my tractor's lug nuts. The rear rims are deep enough that I need to use an extension on my torque wrench. Way in the back of my mind, I have a memory from high school shop class (God bless you, Mr. Sveck) that adding an extension changes the torque actually being applied, as compared to the setting on the wrench. Is this true, or just the aftermath of too much partying after school? And if true, is there an easy way to account for the difference?

I greatly appreciate your thoughts and insights. Thank you.

Nick

 

[Monster5601]

I don't know for sure but I would assume that given a long extension, it would absorb some torque (or twisting action) but, how much I don't know. Then again, does it really matter in this case if your wheel lug nuts are +/- a few percent keeping in mind that torque wrenches are usually in the range of +/- 4% of accuracy?

My tractor specification calls for wheel torques in a range of (I forgot the actual numbers but something like) 145 to 160 foot pounds.

How to calculate what the extension would absorb would be tough because, for example, an extension designed for impact use is softer and would absorb more twisting. How would you be able to find this data for various extensions?

 

[J_J]

You might try these.

http://www.asedeals.com/video_accutorq_sockets.wmv

Amazon.com: Genius Tools Torque Extension Bar Set, 1/2-Inch Drive - 10 Piece: Home Improvement

http://www.torquestick.com/images/torque_chart.pdf

 

[Monster5601]

I have torque bars that I use with my impact tool (for cars) but, if you don't have an impact tool they have no value.

 

[Ductape]

I wouldn't worry about using an extension. I can't see how it would matter in your application.

I feel fortunate that I have a torque meter built into my elbow..... so I've never needed to own a torque wrench !

 

[mwb]

For every action there is an equal and opposite reaction. Using an extension between your wrench and a socket has no effect on the torque transmitted to the nut. Extensions on the square drive (including universal joints) will not change the "click point" of the wrench. Think of the socket and extension as a drive shaft - it can't create more or less torque if the force is transmitted axially.
The only way an extension can affect your torque is if it makes the the moment arm longer (like using a crows foot adapter).

If you are using an extension you will have to support the head of the wrench (no brainer here); the force you apply to the handle will want to make the wrench fall off. This also does not affect the torque applied.

Check here, under "torque facts" menu for some other info CDI Torque Products, America's Largest Manufacturer of Torque Equipment

 

[Famah]

Thanks mwb. I guess it was my parking lot exploits...

And I agree with the others that said it really doesn't matter for lug nuts. I was just curious. Thank you all for responding.

Nick

 

[RoyJackson]

Yes, you'll lose a bit of the torque value with an extention (or a crowsfoot,for that matter).
Do some research and you'll find a formula to factor in the extention.

However, I just add couple ft-lb's (or Nm's, if you into metric). One or two extra should do the job.

Just remember that torquing is not only to ensure the correct tightening of a fastener, it's to prevent overtightening, so don't go overboard on that torque value.

 

[rjmack]

don't forget the never-seize.

 

[Transit]

Nick, i can understand your concern, there are many ways to measure and set torque. Pro mechanics use impact wrenches because they are fast and powerful, too powerful in fact. So, to keep from over torquing the bolts they use torque rods to tame the guns.

The typical click type torque wrench is + - 3% accurate. There are wenches that set torque by angular displacement which are mostly for special applications.

If you set the torque to the midrange for the application you can't go wrong.

If you use a lubricant or anti seize compound than you must de-rate the torque. The easiest way to de-rate is to use the lower value in the range.

Lots of torque how-to sites to see if you wish.:thumbsup: