How much torque is loss with extensions and swivels

[UncleDave]

Originally Posted by Alfred_B
When it twists, the force applied is converted to heat. I find it hard to believe that the extensions do not twist.


They do - if you put a degree wheel on the amount of rotation it takes to reach a given torque you'll find it increases per connection point.

 

[supton]

In the video, static application of force, twist does not matter. Put another way, you could apply the force and walk away.

Now if an impact wrench is used, then that is different. The sudden force does get lost in the twisting, and you are right that loss. The extension is acting like a spring and softening the blow to the bolt. I believe acceleration comes into play also--the end with the wrench gets the sudden impact, the extension twists, and but before the entire shaft can transfer the torque down, the impact wrench has let up. Resulting in a different acceleration at the bolt end. With a resultant loss of torque at the bolt.

 

[Alfred_B]

So if we use a Twizzler instead of an extension, it would torque the bolt with the same success if we are to believe that video?

 

[supton]

Originally Posted by Alfred_B
So if we use a Twizzler instead of an extension, it would torque the bolt with the same success if we are to believe that video?

The Twizzler would be ineffective as it'd simply break. Or if you stopped short, you'd find 1 ft-lb going in on one end and 1 ft-lb coming out on the other end. Again, not while using an impact, but just static forces. Using an impact with a Twizzler might lead to confetti.

 

[ABN_CBT_ENGR]

Originally Posted by Alfred_B
So if we use a Twizzler instead of an extension, it would torque the bolt with the same success if we are to believe that video?


Sup and UD pretty much laid it out so let me try saying the same basic thing with different words.

This is basic power transmission and shaft design

Torque in always equals torque out- that's a fact.

Makes no difference if an extension is 1 inch or 1 mile

That said, everything being equal, there are only 2 things that can alter that relationship- they must be identified and then either accounted or compensated for. ( another way is you de-rate the final torque from the input torque or you "over torque" the input to give the required torque at the output)

1- the "lost motion" ( defined as the torsional losses at a given load where TDC at the driver is not the TDC at the driven until they move together in time)- that has to be calculated and accounted for usually in additional arc

2- any angle from center axis other than 0 ( this can be tangent like a swivel or u joint or an arc from a deflection)

So, if 1&2 are accounted for, torque will be 1:1 regardless- if they are not then there will be a derating.

 

[brages]

consider the "torque stick"

 

[Alfred_B]

Originally Posted by ABN_CBT_ENGR
Originally Posted by Alfred_B
So if we use a Twizzler instead of an extension, it would torque the bolt with the same success if we are to believe that video?


Sup and UD pretty much laid it out so let me try saying the same basic thing with different words.

This is basic power transmission and shaft design

Torque in always equals torque out- that's a fact.

Makes no difference if an extension is 1 inch or 1 mile

That said, everything being equal, there are only 2 things that can alter that relationship- they must be identified and then either accounted or compensated for. ( another way is you de-rate the final torque from the input torque or you "over torque" the input to give the required torque at the output)

1- the "lost motion" ( defined as the torsional losses at a given load where TDC at the driver is not the TDC at the driven until they move together in time)- that has to be calculated and accounted for usually in additional arc

2- any angle from center axis other than 0 ( this can be tangent like a swivel or u joint or an arc from a deflection)

So, if 1&2 are accounted for, torque will be 1:1 regardless- if they are not then there will be a derating.


That's exactly what I have been saying. In real life situation you are never going to have torque in = torque out. An extension bar is real life situation and you are going to encounter your point 1 the effect of which will depend on the engineering of that extension bar.

 

[ABN_CBT_ENGR]

Originally Posted by Alfred_B

That's exactly what I have been saying. In real life situation you are never going to have torque in = torque out. An extension bar is real life situation and you are going to encounter your point 1 the effect of which will depend on the engineering of that extension bar.


Ahh, I think I see the disconnect now.

I think you may be confusing the difference between arc force ( energy required to turn to a given value, ie "torque) to do work versus

arc length ( the distance in degrees, minutes, seconds) required to get there ( what we often call clearance, backlash, slop, "twist", flex etc.) will often change and get longer

You will always have numerous factors influencing arc length but once they are brought to load equinox for a given value ( assuming that value is within the limit of the member)- torque will be 1:1

 

[brages]

There is a difference between using an impact wrench like the op and applying the load steadily. The extensions limit the effectiveness of the impact wrench, in fact torque sticks are sold for this purpose.

 

[CR94]

Originally Posted by ABN_CBT_ENGR
... Torque in always equals torque out- that's a fact.
Makes no difference if an extension is 1 inch or 1 mile. ...
In the case of impact loading, that's a fact only if we can assume the extension is completely rigid and does not have a significant moment of inertia.

 

[ABN_CBT_ENGR]

Originally Posted by CR94
Originally Posted by ABN_CBT_ENGR
... Torque in always equals torque out- that's a fact.
Makes no difference if an extension is 1 inch or 1 mile. ...
In the case of impact loading, that's a fact only if we can assume the extension is completely rigid and does not have a significant moment of inertia.


Did you read the rest of the post?