Teccy Torque Thought

Chrisw8 · May 31, 2013

Don't know why I'm asking this

........perhaps I should lay off the cider :beer2:.....but It's been niggling me for a few days,,,,,,

If you add an extension bar to your torque wrench........does it affect the setting? :confused2::confused2:

jamesmartin · May 31, 2013

no ,just means your pulling further but not as hard

Dr_evil · May 31, 2013

No, you'd just increase the ease of which its applied I think

IIRC When I calibrated my wrench it made a difference because the weight was 0.5m away from the spindle input so you had a leverage/moment going on when calculating, therefore to lift 20kg with the wrench and get it to click I needed double the setting on the wrench.

I.e. with the wrench set to 40NM I could use a 20N weight as the lever increased the effort needed by the wrench spring to activate.

Been a while since I did it but if I saw the machine again it'd come back to me, very simple leverage mechanics but thats for a horizontal moment, you're creating a vertical moment about the pivot point

Chrisw8 · May 31, 2013

no, I mean an extension bar between socket and wrench.

jamesmartin · May 31, 2013

still no

Chrisw8 · May 31, 2013

ok. that answers that then.

Dr_evil · May 31, 2013

Dr_evil said:
No, you'd just increase the ease of which its applied I think

IIRC When I calibrated my wrench it made a difference because the weight was 0.5m away from the spindle input so you had a leverage/moment going on when calculating, therefore to lift 20kg with the wrench and get it to click I needed double the setting on the wrench.

I.e. with the wrench set to 40NM I could use a 20N weight as the lever increased the effort needed by the wrench spring to activate.

Been a while since I did it but if I saw the machine again it'd come back to me, very simple leverage mechanics but thats for a horizontal moment, you're creating a vertical moment about the pivot point

Remembered now

wrench turned a wheel which in turn lifted a lever hence having to work the moment calculation into it. But as yours is a direct force its fine as James said

Brown · May 31, 2013

T'other way round surely? A 40N force at one metre is equivalent to 80N at half a metre and 20N at two metres, as I remember school science. The longer the lever the less hard you have to press to achieve the same moment.

Dr_evil · May 31, 2013

Brown said:
T'other way round surely? A 40N force at one metre is equivalent to 80N at half a metre and 20N at two metres, as I remember school science. The longer the lever the less hard you have to press to achieve the same moment.

I'm sure it was that way round, been a few months since I played with it but I think it was that way because it was turning a wheel which in turn lifted the weight, it was a modified torque machine which you'd generally use to find the angular deflection at a certain force

LRD90tdi · May 31, 2013

Brown said:
T'other way round surely? A 40N force at one metre is equivalent to 80N at half a metre and 20N at two metres, as I remember school science. The longer the lever the less hard you have to press to achieve the same moment.

Correct.

Tom

Jongould · May 31, 2013

Yes it will affect it, the extension bar itself will take a small amount of the torque applied and twist itself, the difference is so negligible on a vehicle application though that its not worth worrying about, if it was NASA then they would take that into the calculations, land rovers though, not so much...

Chrisw8 · May 31, 2013

I must stop drinking. !!!

Thor1950 · May 31, 2013

Jongould said:
Yes it will affect it, the extension bar itself will take a small amount of the torque applied and twist itself, the difference is so negligible on a vehicle application though that its not worth worrying about, if it was NASA then they would take that into the calculations, land rovers though, not so much...

was wondering if anyone would pick up on that. A impact extension would flex less. Like Jon said unless you are a rocket scientist, or a jet engine mechanic, or nuclear reactor builder makes no difference

jamesmartin · May 31, 2013

Thor1950 said:
was wondering if anyone would pick up on that. A impact extension would flex less. Like Jon said unless you are a rocket scientist, or a jet engine mechanic, or nuclear reactor builder makes no difference

it might flex a little but the torque will still reach the bolt unless extension twists and stays like that ,whats put in has to come out unless its performed some work like twisting extension into a spiral bar

jamesmartin · May 31, 2013

Brown said:
T'other way round surely? A 40N force at one metre is equivalent to 80N at half a metre and 20N at two metres, as I remember school science. The longer the lever the less hard you have to press to achieve the same moment.

but the further the lever needs to travel

LRD90tdi · May 31, 2013

jamesmartin said:
it might flex a little but the torque will still reach the bolt unless extension twists and stays like that ,whats put in has to come out unless its performed some work like twisting extension into a spiral bar

James is right - unless the torque was applied for a very brief moment (such as an impact driver would exert), then the full force (torque) would be applied.

Losses in drivetrain are down to friction of moving parts, and energy is lost through heat and sound as we know, but in this example once the force is applied (and kept on) there isn't any measurable heating of the extension nor is there any noise produced.

Tom

Jongould · May 31, 2013

jamesmartin said:
it might flex a little but the torque will still reach the bolt unless extension twists and stays like that ,whats put in has to come out unless its performed some work like twisting extension into a spiral bar

It depends where your measuring the torque from, the bar will remain under tension and therefore some of the energy is retained in the bar, if you have the torque gauge on the wrench then you would need to add the torque stored in the bar, if your measuring at the point of contact (the bolt) then yes your right.

LRD90tdi · Jun 1, 2013

Jongould said:
It depends where your measuring the torque from, the bar will remain under tension and therefore some of the energy is retained in the bar, if you have the torque gauge on the wrench then you would need to add the torque stored in the bar, if your measuring at the point of contact (the bolt) then yes your right.

I agree the extension bar is storing energy, just like any flex in the torque wrench itself will do so too, but you're wrong that the torque will differ from one end of the extension to the other.

Look at it this way, if you hang a 5kg weight on the end of a 1m lever bar you have the same value (torque) as you do if said lever bar flexes like a cheap ruler; the force is still transferred to the nut, and is still directly proportional to the mass and the distance of the lever.

Flex/tension/spring (the stored energy) is only relevant if the load is applied for a very brief moment, and that energy can be absorbed before it is transferred in full.

Tom

SteveD · Jun 1, 2013

I was always taught that extensions did affect the torque but that was in an aircraft environment. In fact we had calibrated torquemeters on the wall so you could try extensions out and set the torque wrench accordingly. When working on vehicles I've never worried about it as the torque range specified is usually quite wide and I just set the wrench for the upper figure, that way if a bit is lost it won't matter.

Using a UJ or a wobble extension on a socket is a different matter though and will make a massive difference.

Paul D · Jun 2, 2013

Jongould said:
Yes it will affect it, the extension bar itself will take a small amount of the torque applied and twist itself, the difference is so negligible on a vehicle application though that its not worth worrying about, if it was NASA then they would take that into the calculations, land rovers though, not so much...

You'd be surprised ..

When I worked at Desoutter/Georges Renault, we built machines to tighten the Land rover hubs/brakes/axle assemblies together, dc brushless motorised torque tightening, fully computer controlled. I did a lot of the setting up to determine the torque to tighten (breaking bolts and assemblies and analysing results) and thereafter the programming sequences.

Basically every assembly was tightened to about 5% below it's elastic limit, using a sequence that might go along the lines of tighten to small torque, loosen, tighten to higher torque then add 30 degrees rotation, loosen then tighten to final torque with another 30 degrees rotation.

The reason for adding rotation on is 'cos when it's done as accurately as we did it, it's a far more repeatable and definite measurement of applied torque, especially in a production line environment. the machines had angle measurement and transducers built-in so we could measure accurately enough, and do it repeatedly to better than 0.3% accuracy of tension in the joint.

.... and that was 15 years ago for the L322 and 'newer' models that have come out since then ... dunno what they use now ..

Teccy Torque Thought

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Old, nackered 'n broke, but the Landy is fine . :)

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