Torque settings and extensions

[prb51]

Often I can't get to a nut/bolt without an extension on my torque wrench. I've had some mechanics tell me they swag some additional lbs. depending on the length of the extension. i.e 5 ft.lbs for a 3" ext. etc.
What say you?

 

[Mickey Richaud]

Good question!

Found this when I rebuilt the engine for the TR8:

https://www.norbar.com/torquewrenchextensioncalculator.php

Mickey

 

[Mickey Richaud]

But that is only for the length of the wrench - See this post for adding a socket extension - no change needed:

https://home.jtan.com/~joe/KIAT/kiat_3.htm

Mickey

 

[prb51]

Mickey,
Great sites and thanks. Good to know stuff.

 

[martx-5]

Good question!

Found this when I rebuilt the engine for the TR8:

https://www.norbar.com/torquewrenchextensioncalculator.php

Mickey

In the case noted in the link, that applies when you are actually extending the length of the torque wrench. What the OP is asking about is putting an extension on a socket, and then torquing the bolt. I don't have an answer to that question, but knowing if the extension has an affect would be important to know. And then how in the heck would you calculate that?? All extensions are NOT created equal. Some will twist more then others even if they are both 1/2" or 3/8".

So, who out there has the answer??

Edit: Mickey had the answer before I got my post up. Well, this is good to know.

 

[rlandrum]

Hmm... Seems easy enough to determine the amount of torque lost to the extension.

Torque bolt without extension to 75 ft.lbs.

Now remove the bolt with the torque wrench with extension set at 75. If it clicks before it releases, then bump to 76. Continue until it releases.

The difference should be the amount of torque absorbed by the extension, right?

 

[TR3driver]

The difference should be the amount of torque absorbed by the extension, right?

Nope. It takes substantially more torque to start a bolt moving than it takes to keep it moving. The difference is commonly called 'stiction' (from "static friction"). If you just torque a nut to 75 ftlb, then set your wrench to 80 ftlb and try again, usually the nut won't move at all. But if you mark it's position, then loosen it and tighten to 80, it will have turned farther. This is why, when you retorque head nuts, you should loosen them slightly first.

All extensions are NOT created equal. Some will twist more then others even if they are both 1/2" or 3/8".

Twist is not the issue (assuming you are using a steady torque wrench and not an impact wrench). However, contrary to the link Mickey posted, I believe there is an effect that makes using an extension slightly less effective. By moving the plane of where you pull on the torque wrench handle away from the plane of the bolt head, you introduce a bending moment that I think increases side load on the bolt and hence increases friction. The way around that is to support the head of the torque wrench so there is no extra side load on the fastener (which is good practice anyway, IMO, since otherwise it tends to rip the socket off).

But since bolt torque is a very inexact measurement of what you really want to know anyway (clamping force), I doubt it makes much difference.

Oh yeah, I believe the other link was mistaken as well. Adding a lateral extension even at 90 degrees does change the applied torque. What's important is the length of the lever arm from where you are pulling on the wrench to where the bolt/nut is. So adding a link at 90 degrees increases the torque, because it moves the handle farther away from the pivot point.

 

[DNK]

I just knew Randall would have an answer when I started reading this.

 

[startech47]

The twist in the extension does not matter as long as you are raising the force slowly enough to be in a static situation. The socket extensions the gas stations use on impact wrenches are dynamic devices and depend on calibrated flex in the device.

 

[Mickey Richaud]

SHEESH! This is why I'm a priest! /bcforum/images/%%GRAEMLIN_URL%%/jester.gif

 

[Twosheds]

Oh yeah, I believe the other link was mistaken as well. Adding a lateral extension even at 90 degrees does change the applied torque. What's important is the length of the lever arm from where you are pulling on the wrench to where the bolt/nut is. So adding a link at 90 degrees increases the torque, because it moves the handle farther away from the pivot point.

No. Adding a lateral extension at 90 degrees does not change the applied torque. It does not change the arm, so it doesn't change the torque. I used to teach this in A&P school. One student didn't believe me. He made a bunch of different length lateral extensions at home and we tried them on a torque wrench on our torque wrench calibrator. The lateral extensions did not change the torque when used at 90 degrees.

 

[Guest]

SHEESH! This is why I'm a priest! /bcforum/images/%%GRAEMLIN_URL%%/jester.gif

Me too!



Wanna complicate it further, try having to use a crow's foot with your torque wrench, like on a header, etc.

 

[Twosheds]

Wanna complicate it further, try having to use a crow's foot with your torque wrench, like on a header, etc.

Same thing, Bill. Just turn the crow's foot to 90 degrees to the torque wrench handle and the torque won't change.

 

[TR3driver]

No. Adding a lateral extension at 90 degrees does not change the applied torque.

After further consideration, I see you're right, John ... IF you add the caveat that the force applied to the torque wrench is only at right angles to the wrench itself. But pushing on the end of the torque wrench will apply torque to the fastener without changing the reading at all.

 

[DrEntropy]

Hedge yer bets, Randall.

Wanna complicate it further, try having to use a crow's foot with your torque wrench, like on a header, etc.

Same thing, Bill. Just turn the crow's foot to 90 degrees to the torque wrench handle and the torque won't change.

THANK you, John!!!

/bcforum/images/%%GRAEMLIN_URL%%/thumbsup.gif

 

[AltaKnight]

Errrr....my head hurts, where's me spanners...

 

[prb51]

Very good stuff, specifically the 90 degree addition as that will work in some tight spaces.
Ok, that was easy for you guys so...
If a train left Chicago at 2:30pm and traveled at 60 mph how ....I always hated those boogers.

 

[amcboy]

Hmmmmmm.....

 

[Bob Buxbaum]

Twosheds and the others that state there is no need for any "adjustment" for an extension at 90 degrees are correct. I sold torque wrenches as a Snap-On dealer for 19 years. People that say that once a fastener is "bottomed", a second pull will be misleading. An extension WILL absorb power from an impact tool, but not a torque wrench. Frankly, given the allowable tolerances of a torque wrenches, one should be more concerned with the quality and accuracy of the torque tool you own than a minuscule error that could be created by an extension.

 

[amcboy]

Bob, now that is valuable advice!

Ever compare types of TQ wrenches?

Scaaary sometimes.

Advice: Get yours checked/calibrated!

Just my .02