What is a torque reaction arm and how does it work?

The simple explanation.

A reaction arm is attached to annular of a torque multiplier, acting as a ‘stopping’ point for it to grip onto. Without one, the gears within the tool would simply keep spinning. With a reaction arm in place the reaction torque (the opposite of the force being applied to the bolt) is absorbed and the tool can do its job.

The Newtonian explanation.

Isaac Newton’s (all-time physics genius) third law dictates that for every action there is an equal and opposite reaction. When applied to torque tools, this basically means when something spins one way, something else has to spin the other way to equal things out.

This is a pain for our line of work because we want all the torque we are applying to be used for loosening the bolt, and not be lost in some 17th century physics void called a torque reaction. The solution is the reaction arm, which stops the annular against a reaction point and absorbs the torque reaction, allowing our equipment to work.

Calculating reaction force.

When using multipliers and PneuTorques the reaction point must be capable of withstanding the reaction force or you will damage the reaction point, your tool and possibly yourself.

Therefore, great care must be exercised where the reaction is taken when applying high torques to studs and bolts. The following formula helps you calculate the force at the point of reaction. The greater the distance, the lower the force.

• D = Stud Diameter
• Formula for calculating area of the stud = (π x D2)/4
• Formula to calculate shear force = Reaction force/Area of stud

What to do if the standard reaction arm is not suitable.

All Norbar tools come with a standard reaction arm – however this cannot be suitable for all applications. There are literally infinite configurations of bolts and machinery and it would be impossible to design one solution to meet them all. If your reaction arm doesn’t suit your application the only option is to engineer one that does – anything else and you risk damaging equipment or, way more importantly, your people.

Norbar’s engineered to order solutions.

We offer a highly skilled in-house engineering team to design and meet your specifications. We’ll work with you to design a reaction arm that gets the job done so you can get back to doing what you do best – no physics degree needed.