I thought this was a real tech site compared to every other site I've ever been on. I really was not trying to start a pissing match between me and said moderator. Apparently if you can't prove something, you lock the thread and post youtube vids of 5 sec drag cars that you helped build to some how prove your point... I'd like to re open the thread, sadly in the BS section, to get a real tech answer confirmed. If you use a straight 1/2" extension that does not add to the lever arm of the torque wrench, do you need to adjust the torque? I was taught NO by my FAA DME's in A&P school. I've read all over the interwebs looking for an answer to the contrary and have not found one. But most answers are speculative forum answers. I'd rather settle this from an engineering standpoint e.g. Tom Vaught, Andy Dorsett etc or if someone can find some official literature on the subject...

Here's the original thread

https://www.theturboforums.com/threads/368515-Retorque-heads

seriously not trying to start shit, but locking a thread seems a bit ludicrous

 

I'm not an engineer, but in my experience as an aircraft maintenance technician. I use mostly 1\4" drive. and I've experimented with a long extension and then with the extension removed and the fastener did turn. I believe it takes so much torsion on the extension to even start moving the fastener then you hit your torque and the torsion of the extension is still present until you let off the fastener. I also think this becomes negligible while using a very short extension (not much torsion in a 2-3" 1/2" extension). and what about those impact extensions that are colour coded for torque. different operation I know, but just shows you there is a torsion load at a certain size of shank.

IMO !!

 

True. I also used to work at discount tire and dealt with the colored impact torque extensions. Those are designed to be used on an impact gun that would load/unload rather quickly and it is certainly a different theory of operation compared to the slow sweeping turn of a torque wrench. I too have messed around with 1/4 drive extensions at work and get what you are saying. My opinion is that the longer the extension, it eats up a certain amount of torque per inch, once the extension twists to where it becomes solid again, all torque transfers to the fastener. If you use an 24" 1/4 drive extension, it might take 90in/lbs just to load the twist from that extension, but if your only torquing the fastener to 45in/lbs, it might not transfer all the torque (obviously all hypothetical numbers). I don't think a 4" or 6" 1/2 drive extension comes anywhere near that type of twist and I think 100% of the torque is transferred and no correction need be applied. The cross sectional area is exponentially larger therefore making the torsional strength of the metal much more rigid. I very we'll could be wrong

 

Theory of radial torque still applies. The longer your extension shaft (of the same diameter) the more torque loss the fastener will see. The diameter of this extension is what you should really be concerned about. If it's 6" long and 3/8 in diameter, I would expect some tq loss when going to 90 pd-ft. If that extension is 1" in diameter, I would expect much much less. On the flip, if it was 1/4" then it would experience a lot of loss.

Think about it like this... What if you have a regular sized 1/2" drive extension that is 100 feet long. And you want to tq your stud to 110 pd-ft. Do you think the fastener would see the full 110?????

 

No I don't think in that situation it would transfer all the torque. But I think there is more or less a cut off torque number for a given extension length/diameter where 100% of the torque transfers to the fasteners. At some point all of the twist is removed and all of the torque is transferred.

 

I wouldn't say his last post was malicious by any standard. But he did end it without allowing any technical rebuttal.

 

Seemed more of a "here's why my opinion is the only one that matters", close thread.

 

That is what the discussion was about. The cut off number for no torque being lost is ZERO. Now, that can be mitigated by increasing the size and torsional rigidity of the extension being used. Why don't you use a 1/4" extension to tq 1/2" head studs? No torque would be lost correct? Once the extension stopped twisting it would transmit all the tq to the fastener correct? Obviously i'm being facetious, but you understand what I am saying.

I can prove the theory about loss of tq through the extension,but I want you to understand it from a practical stand point. Even a short 3" long 1/2" drive extension will suffer some tq loss IF it is twisted enough. All metals have a stress/strain limit. Steel is very tough, but if twisted hard enough, it will start to give. When it does, some of the tq being inputted into the material is lost in twisting the material and the end of the extension does not see the same force as the input side.

 

i don't know why people have a hard time understanding this it is simple geometry that is(was?) taught in jr high.

 

Jared, I will also say that there is a limit to this torsional loss. If you use a 12" ext at 30pdft you might not experience any measurable loss. That same extension at 200pdft might see 20pdft loss. It is all dependent on the material, and the measurements of the tools in question. It's due to the materials modulus of elasticity and modulus of rigidity.

 

I've got yer modulas of rigidity right here, Pally.

 

Not to get in the middle of the pissing match but this is out of the torque wrench i bought last nite, maybe it will help. lol

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The torsion of an extension WILL subtract from the final torque. Try it yourself as mentioned above, torque with an extension, then go back and check it with just a socket, 9 times out of ten, it will go tighter before it clicks, which lends a lot of credence to going up a little on the setting if you must use an extension.

 

LOL made me laugh!

All that being said. I don't think anyone would be dumb enough to use a 2' extension to tq head bolts (what started this whole thread anyway). sometimes you have to but most people would use the shortest one they could comfortably fit if needed at all. and what I said before a short one would give negligible effects. Im surprised that no one brought up the proper use of a TQ wrench because Ive seen "professionals" use it wrong. but I suppose that's really my opinion on that as well.

 

ARP and Snap-On say an extension won't affect torque readings, but what do they know. We are splitting hairs here anyway as it's likely going to be outside the accuracy of the torque wrench itself.

 

I'd say a 1/4 drive adapter on a 1/2 head stud would yield and look like a twizzler or snap in half lol.

I get what you're saying though. I could also see that you'd lose torque with an extension because you're tipping the wrench slightly off of the fastener.

On the other hand, what about axle wrap? I'd argue that once the leaf is done wrapping, all torque is transmitted to the axle. Is that wrong? I think that's a similar idea.

 

It is exactly the same. And the axle twists, just just the extension.

 

No doubt we're splitting hairs, I'm sure its' a very small amount that the tq is changed, and I don't ever account for it myself, but the fact remains... Ahh nevermind.

Just torque your shit til it's tight, people!!!!

 

Well I got my engineering answer from Disney. I guess I was wrong. Twist is a loss and does not transfer all torque to the fastener. I am happy now and will shut up...