Length dependent Vs Length independent Torque wrench

Length dependent Vs Length independent Torque wrench

?What Torque is

.As we know Torque is measure of Force that can cause an object to rotate about an axis(Pivot Point)

?What Torque wrench is

.Torque Wrench is a Tool to apply a specific Torque to a fastener such as a nut or bolt

Usually Torque wrench made in a form of socket wrench. We have to set our desired Torque first. Then we have to apply force on the A point(center of handle) when the desired torque is achieved torque wrench rotate an small step around Pivot point and make a click sound. Which make clarified target torque on the

.square drive is obtained

?What does length dependency mean in torque wrench

Length dependency on torque wrench means that by changing the position of apply force (hand) the amount of torque applied in square drive will be different. Despite the fact that set torque in the Torque wrench has not changed

?What’s make torque wrench length dependent

The issue is, in this type of torque wrench at the click time, the pivot point (axis of rotation) is not same as our

target torque point at the square drive where we want to fasten a bolt or a nut

When we Adjust torque wrench to apply certain torque on a bolt or nut, because of difference length between Pivot point and square drive with F(force) the amount of torque felt in pivot point is different with square drive. As we can see on diagram, the Target Torque is more than torque in pivot point. So the manufacturer company consider this difference for calibration calculation

Now imagine that we have not changed the amount torque that we set on a torque wrench. But put our hand on a O point instead of A. So torque wrench will click on the same amount of torque on pivot point but as we can see on diagram the amount of torque apply on the square drive will be more than our target torque. Note that if the apply force is placed very close to the Pivot point the desired torque can increase to infinity

On the other hand, consider if apply force placed far away from A point like U point without changing the set torque on a torque wrench. As we can see on diagram our apply torque will be less than our desired torque

In all three cases that we have reviewed. The amount of adjustment torque in the torque wrench has not changed. Therefore, the click torque was the same at the pivot point. But the issue is that the amount of torque applied in the square drive has changed. This issue shows the importance of the correct placement of the hand(apply force) on the torque wrench

To understand the drawn diagrams, it is necessary to have some knowledge in the field of physics. For further simplification, we consider a numerical example with a different point of view

 :Numerical Example

This figure is an exaggerated schematic image of a Torque wrench. which we have  considered to express the issue more easily

Assume that we want to apply 36 N.cm on a bolt or nut in a square drive so torque wrench should adjusted to 36 N.cm

And A is the place that company recommended to apply force. So we should apply 6 N at A. So we apply 36 N.cm to a bolt or nut and click in pivot point happen. but in pivot point our sensed torque is 24 N.cm

Therefore, the company considers that when the applied torque on the pivot point is 24 N.cm, the applied torque on the square drive must be 36 Nm and click happen

Now consider operator adjust torque wrench 36 N.cm but apply force at O point instead of the right place at A point. As we mention company calibrated torque wrench in a way to make click when apply force reached 24 N.cm in pivot point when it’s adjusted to 36 N.m. so operator apply 12N  and then click happen but you can see our torque applied on square drive will be 48 N.m instead of 36 N.m  . and its over torque

One more time consider torque wrench adjusted to a 36 N.m. but operator applied force in U point instead of right place. As we told torque wrench will be make click when torque reached 24 n.m in pivot point so click happened when operator applied 4N. and there for we have 32 N.m in a square drive so not enough torque applied

Therefore, we conclude For a specific set torque, an infinite output torque can be obtained by

 changing the place of force application

?Are All of Torque wrench length dependent

The answer is no. Torque wrenches that have same square drive and pivot point are length independent. Which means that the operator can put his hand and apply force wherever he

wants