Effects on torque reading

[sbc438]

OK here's the delema. I have to develop a torque wrench extension to reach a bolt under a verical. What I have come up with is a box end extending horizontal for 3 inches and then 90 degrees down for 6 inches to the torque wrench. My problem is what will the reading on the wrench be @ 51.6 lb ft on the bolt. It's been a long time but I don't think I'm that rusty. I can't seem to come up with a factor to adjust that isn't dependent on the length of the torque wrench being used.
Someone shed some light on this for me (I know I'm going to kick myself!!)

jwj

 

[TheTick]

Statics 101...

Torque1 x ArmLength1 = Torque2 x ArmLength2

therefore

Torque2 = Torque1 x ArmLength1 / ArmLength2

 

[GregLocock]

Put your steel toe-caps on

What is the bending moment in a cantilever length L at a distance x from the encastre wall ?

What is the torque at the tip of the cantilever, where a pure force is being applied?

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[TheTick]

Remember that "ArmLength" is only the component of the arm that is perpendicular to the axis of the bolt you are turning.

 

[sbc438]

Assuming the torque wrench is 1 (A2) ft and the extension is .25 ft (A1= 1.25) my torque wrench is going to read 64.5 lb-ft? Now since this is ArmLength dependent...what if the operator chokes up on the torque wrench and A1 is .75 feet in stead of 1 foot A1/A2 goes from 5/4 to 4/3 changing my T2 but keeping my T1 51.6 lb ft.... Am I correct that T2 will change? Am I missing something. My problem here is If I'm correct I can't use an extension due to operator infuence.

Now if you replace T with Force applied (F) the shorter lever arm will require higher applied force to reach the torque I can live with that as long as Delta (F) off sets the factor of Delta A1/A2. Follow

 

[desertfox]

Hi sbc438

If you set a torque wrench to a setting it will click off at that setting, however due to the elasticity in your torque arm it may affect the pre-load in the bolt.

regards

desertfox

 

[chicopee]

Remark for The Tick- the torque for presumably nut or cap screw does not change for whatever length one decides to use on a torque wrench extension or "cheater".

So, T=F1*L1=F2*L2=F3*L3=.....Letting L1 be the original length of the wrench and L2 be the new length of the improvised wrench then the new force F2=T/L2=F1*L1/L2.
Only the force and length change for the required torque.

The torque remains constant for whatever length "cheater" is being used. So if the requirement is 40 ft-lbs, when a "cheater" is added , that value must still be maintained on the torque wrench.

By the way OSHA will cite any employer for home made and unauthorized cheaters

 

[GregLocock]

????????????????

Sorry, I have either completely misunderstood your explanation or it ignores the OP's idea, which places the torque wrench's measuring axis part way along the lever.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[desertfox]

Hi Greglocock

I think Chicopee and myself read the op's question as just adding length to the torque wrench arm and not that he was
moving the position of the torquemeter measuring axis


regards

desertfox

 

[GregLocock]

Gottit.Wow I'm not surprised the OP hasn't reappeared. 101 indeed

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.