packick

Torque Wrench Question

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Here's something I have always wondered about so I thought I'd pose this question to the Post War Buick gurus.

 

Let's say I want to torque a bolt or nut, to 90 ft. lbs. and I have a 1/2” drive torque wrench. I put the socket on the torque wrench, dial in 90 ft. lbs. on the wrench, and tighten the bolt until it clicks. No problem.

 

Now let's say I add a 6” or 12” extension to the wrench and attach the same socket onto the extension. Would there still be a 90 ft. lbs. torque on the bolt or do you lose some torque because of the extension? Or let's say I add an adapter to go from the 1/2” drive torque wrench to a 3/8” drive socket. Again, would I still have 90 ft. lbs. on the bolt? What about using an adapter and an extension? Still 90 ft. lbs.? And finally, what about using a flex socket? Still 90 ft. lbs.?

 

This doesn't keep me up at nights but I have always wondered.

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38 minutes ago, packick said:

This doesn't keep me up at nights but I have always wondered.

Funny...I have always wondered the same thing.  I assumed that you did and I would always add a little more depending on how much torque was required when adding anything between the socket and torque wrench.  Looking forward to a definite answer.

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As long as the socket is still in line with the drive pin of the torque wrench, the reading does not change.  i.e. the square drive of the wrench still points directly into the square hole of the socket and centered on the nut or bolt head, even if it is 2 feet away (or any amount), the reading is OK.

 

Now, put an extension on the wrench that moves the socket laterally away from the square drive, and now you need to do math. Many pictures of this on the internet*. i.e. if you use a crows foot socket, the reading is WRONG. A crows foot puts the  head of the bolt or nut not inline with the square drive of the wrench.

 

Now, you do need to hold the wrench and extensions so the bolt/nut is still in line with the square drive of the wrench, otherwise you will introduce an error! No swivel sockets..... or wobble extensions....😲

 

*     https://www.engineersedge.com/manufacturing_spec/torque_wrench_1.htm

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A bunch of extensions can act as a spring and limit torque. Thats the principle on which a torque stick works.

 

torque-stick-impact-wrench.jpg

 

Put the socket right on the torque wrench if you can. If you cant, use a thick extension, and as little extra length as you can.

 

Flex sockets and wobbly extensions will behave unpredictably. Never do that unless you have to (and then you cant quite believe the number).

 

With a crowfoot wrench, the actual torque can be calculated based on the amount of offset in the crowfoot.

 

 

 

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Most torque specs have a range. Use the higher end of the range if you are worried about the flex of the extension. If a range isn’t given, it’s a pretty safe bet that +\- 10% is acceptable. 

 

Put the crow’s foot or torque adapter 90° to the wrench centerline and you don’t have to do math. 

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As I understand it, the torque wrench will give way at the set lbs no matter the length of the extension.  But as others stated, always use a straight strong extension.   

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Torque Sticks are designed to twist and limit torque. Typical 3/8" straight extensions should be beefy enough for 150 or so foot pounds (1800 inch-pounds). 1/2" extensions should be 400 ft-lbs (5000 inch-lbs). If you see the extension twisting, then torque at the end of the extension will be lower than at the wrench.

 

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In general, the "extension: should be as short as possible and still get the job done.  From what I've seen, IF the extension starts to flex from the turning force being applied, then you are probably in some "territory" you shouldn't be.  OR you need an extension appropriate for such use.

 

The first torque wrench I bought was a "beam" style torque wrench.  They kind that was all you could get in the earlier '60s, before the "clicker" wrenches.  Much easier to use the late-model clickers, by observation.  Just set it and wait for the "click" feel and sound.  BUT if you really want to "feel" things, then the beam wrench is the one.  A correctly-calibrated clicker is probably the best thing to have, generally.

 

In the '90s, the "big thing" was the Torque Sticks for wheel lug nuts.  Color codes for the level of torque the lug nuts were supposed to be tightened to.  Almost always used with a pneumatic impact wrench.

 

NTX5467

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