How is torque determined

They need to consider platings, coatings, lubricants and thread-lockers. They need to think about how the fastener will be installed.

Is it enough to tighten the fastener to a specific torque? Or will both torque and angle need to be controlled? Regardless of the product, everything starts with calculating how much clamping force is needed for the assembly to operate correctly and safely.

This is determined by the loads and conditions to which the joint will be exposed, plus a safety factor. Engineers must choose a fastener or fasteners that can successfully transmit that clamping force between the parts and bear the stress of it. But all fasteners have limits to how much stress they can take.

This is a function of the fastener material and its geometry, including its cross-sectional area and the area of the threads. That limit cannot be exceeded. How much torque that requires depends on the geometry of the bolt and whether the threads are lubricated. Lubricated threads require less torque to get to the same clamping force, because there is less friction to overcome during the tightening. Are you using moly lube or copper anti-seizing lubricant?

Even threadlockers can act as a lubricant initially. The most commonly used K factors arc 0. For a more accurate estimate of the nut factor, engineers can set up a standard fastening test to solve the equation for K. The best way to develop a torque specification is through testing, argues Archer.

The reason to do testing is that friction, run-down speed, part tolerances and other variables can significantly influence the relationship between torque and clamp load. Two types of tests can be run to determine a torque specification: measuring torque and angle to failure and measuring torque and angle to a specific tension. In either case, the goal is to find a torque value that applies the most clamp load on the joint without the risk of tightening the fastener past its yield point or, worse, its breaking point.

If you reuse a bolt, you will get different characteristics each time. The number of run-downs needed to determine a torque specification varies. A typical range would be six to 24 run-downs. The answer is both. Load torque is the sum of both friction and gravitational loads. The gravitational force is determined by the weight, or mass x gravitational acceleration g. Load torque calculation is different for various applications. Let's take a look at some common examples to see how the load torque is calculated.

For a pulley drive application, the load torque calculation is pretty straight forward. We need to generate a force at some distance away from the motor shaft definition of torque. This can be calculated by multiplying force F by the rotation radius r. In order to move the load blue box , the motor must generate more torque than this value.

To calculate load torque, multiply the force F by the distance away from the rotational axis, which is the radius of the pulley r. If the mass of the load blue box is 20 Newtons, and the radius of the pulley is 5 cm away, then the required torque for the application is 20 N x 0.

Typically, a safety factor is used so that the motor generates more torque than required to accommodate any inaccuracies in variables used for calculation. The above formula works for applications with friction load or without. In a conveyor application where the load is supported by a surface, friction is constant and is proportional to the load's mass. The following formula is used to calculate load torque for belt drives conveyors as well as rack and pinion drives.

For this type of application, we'll need to calculate force F first before we can calculate the load torque TL. Once we have the F value, then we can plug it into the load torque TL formula. Load torque calculation for rotary index tables uses the same formulas as a belt drive , but it requires a slightly different thought process to determine the necessary variables. In this case, friction occurs at points where the ball rollers support bearings and the table make contact, so radius r will be the distance from the center of the motor shaft to the contact point between the table and its support bearings.

The mass m will be the mass of the table plus load s. TIP : Motor sizing tips. Be careful not to mix and match imperial units and metric units in the same formula. If you need to convert units, make sure it's converted properly; especially the decimal point. Create a personalised content profile. Measure ad performance. Select basic ads. Create a personalised ads profile. Select personalised ads. Apply market research to generate audience insights. Measure content performance. Develop and improve products.

List of Partners vendors. Share Flipboard Email. Andrew Zimmerman Jones. Math and Physics Expert. Andrew Zimmerman Jones is a science writer, educator, and researcher. He is the co-author of "String Theory for Dummies. Updated October 18, Featured Video. Cite this Article Format. Jones, Andrew Zimmerman. Calculating Torque.