WHAT IS TORQUE? WHY DOES IT MATTER?
What is Torque?
Torque is a cost-effective and widely accepted estimate of clamping force. In assembling a build, the torque application specifications are added to ensure the threaded fasteners remain in place and do not vibrate loose.
The concept of torque has been around since Archimedes. You may remember Archimedes from your school days and his quote, "Give me a lever, and I will move the world."
Torque is an application of a lever. In this case, the lever is used to provide a rotational force on a threaded fastener. While the concept is simple, the nuances are more complicated.
Torque must be applied at 90 degrees to the fastener. Any deviation from 90 degrees changes the lever length, which changes the torque output. Deviations from 90 degrees are variables.
While this might not sound impactful, consider the question, "When is it OK to add variables to the assembly process?" If you are adding variables to your assembly process, at what point do you stop?
Given that up to 90% of torque can be used to overcome friction that means that only 10% of torque accounts for clamping force.
Factors That Impact Torque Application
Wrench design is a significant factor in impacting torque application. In physics, a tube bends more readily than a flat beam. In 1924, when Walter P. Chrysler invented the commercial torque wrench, it was a flat beam of steel. While the type of wrenches that are on the market have changed, the physics principle still applies.
It is easy to bend a tube-shaped torque wrench. It is much harder to bend a torque wrench that has a flattened case. Bending a torque wrench during torque application is called sideloading. Sturtevant Richmont torque wrenches have a flattened case. That means those wrenches are harder to bend or sideload during the torque application. That means fewer variables and more accurate and consistent torque application.
The flattened case provides support for the clicking mechanism. It, too, is flat and is guided by lubricated steel ball bearings. This makes the wrench highly repeatable. Those ball bearings also have a very strong impact on durability. Because of the guided movements, there is less wear and tear on the moving pieces. That enhances durability.
Flex Head Design is Not a Solid Torque Strategy
Some companies manufacture their torque wrenches with a "flex-head." The flex-head pivots. While that might make it a little easier to get the socket on the nut, there is a significant drawback. The flex-head makes it extremely easy to deviate away from 90-degree torque application, or easier to sideload the wrench. Now you have just added another variable to the torque equation. Now the operator must vary from their normal routine in how they apply torque. The operator must be certain to keep the wrench at 90 degrees to the fastener.
Interchangeable Heads Can Impact Torque Output
Hard to believe that in this day and age and level of technology that interchangeable heads can impact torque output, but they can and do. Specifically, the cut and held heads are often guilty of this. Why? Because they cut the heads off a wrench and weld that head on to a plug, or a stay, and that goes on the end of a wrench. Some companies give you an alphabet of choices; The problem is that larger heads used on larger fasteners require a bigger plug on which to weld the head.
The result is that those companies sell you two wrenches of the same torque capacity. One wrench for the handling of large fasteners and the other for handling the smaller fasteners. Do you want to buy and calibrate two wrenches for the same torque value when one will do fine?
Why not just by the wrench where all of the heads fit on all of the wrenches? That would be Sturtevant Richmont.
Why Does All This Matter?
Torque is a relatively inexpensive way to estimate clamping force. Clamping force holds things together. Not enough clamping force and nuts and screws can come loose as a result of vibrations. That is also what causes a lot of hydraulic leaks.
Too much clamping force can cause damage. The fastener might be damaged and can't be reused then a maintenance procedure is done. Too much clamping force can also damage components.
See the Case of the Curious Lab Manager for a real-life story on how torque screwdrivers made a difference.