How a torque wrench works

This is a ratcheting click type torque wrench. It's the most commonly used torque wrench available. In this video, we'll take a close look at the mechanism inside to see how it works. Before we jump into the inner workings of a torque wrench, let's first understand how it is used and what are the key components involved. Let's get started. Torque is a rotational force. It is usually measured in foot pounds, A torque wrench is a specialized socket wrench tool designed to tighten fasteners to a predetermined torque value, ensuring consistency and preventing over- or under-tightening of the fasteners, which can lead to issues like stripped threads or loosening. Using a torque wrench to loosen fasteners can potentially damage the tool and affect its accuracy. Torque wrenches have a maximum torque rating, and using them to loosen fasteners might subject them to forces beyond their intended capacity. As you are tightening a fastener, you'll hear and feel a distinct click when the preset torque level is reached. This lets you know it's time to stop applying force, preventing over-tightening. The handle is where you grip the wrench during use, and it's also used for setting the desired amount of torque you want to apply to a fastener. The torque main scale is engraved on the wrench body, with more precise subdivision markings on the handle for micro-adjustments. There's a spring-loaded locking ring used to secure the set torque value, preventing accidental changes during use. Torque setting can be adjusted by first depressing the locking ring and turning the handle to the desired torque setting. Turning the handle clockwise will increase the torque value, and turning it counterclockwise will lower it. When the desired torque level is set, the locking ring can be released to lock the handle. If, for example, you want to set the torque value to 32 inch-pounds, turn the handle until its top edge is even with the horizontal 30 mark on the main scale and the zero mark on the handle lines up with the vertical line of the main scale. Then, turn the handle clockwise until the two mark lines up with the vertical line of the main scale. The torque value is now set to 32 inch-pounds. This is the ratchet head. It allows the wrench to turn the fastener in one direction while preventing rotation in the opposite direction, without having to lift and reposition the wrench for every turn. The direction of rotation can be changed by moving the selector level on the back of the ratchet head. This is the square drive. This is where interchangeable sockets that correspond to the fastener size are mounted. The most common drive sizes available are 1 quarter, 3 eighths, and half inch. The sockets are held in place by a ball detent mechanism. In this example, the ball is spring-loaded. Let's take a look at the ratchet head mechanism. It typically consists of a gear and a set of pawls. The square drive is attached to the gear that can rotate in both directions, and the pawls are the two small spring-loaded levers opposite of each other that engage with the gear teeth. Only one pawl can engage with the gear at any given time. The lever controls which pawl is in contact with the gear, determining the direction in which the ratchet mechanism operates. When engaged, each pawl wedges itself against the gear teeth, preventing rotation in one direction, but the pawl can slide over the teeth in the other direction, creating the clicking sound you hear when using the ratchet. Now let's take a closer look at the click mechanism inside the torque wrench. Right below the ratchet head mechanism, there is a pin that holds the head assembly to the wrench body, which is a hollow metal tube. The pin allows the head assembly to pivot inside the wrench body. At the end of the head assembly, there's a slot where a pivot block makes contact. On the other side of the pivot block is a spacer with another slot also in contact with it. The spacer and pivot block are compressed by a large adjustable spring. Turning the handle changes the tension on the spring via a screw thread. This compression stores potential energy in the spring. When the preset torque amount is reached, the force generated by the spring on the pivot block is overcome. The energy stored in the system is released, causing the block to momentarily disengage and tilt. Simultaneously, the end of the ratchet head assembly hits the inside wall of the wrench body, producing the audible click sound. After the click, nothing prevents the user from adding additional torque. Consequently, click torque wrenches are not 100% safe from over-torquing. It is recommended to set the torque wrench to its lowest level before storing the torque wrench for a long period of time. This releases the tension on the internal spring and prevents creep, which is a slow deformation when subjected to persistent mechanical stress. But how do you keep the handle locked during use? There's a series of grooves on the wrench body along the travel path of the handle. Hidden under the locking ring, there are five holes along the circumference of the handle body. There's a ball captured in each hole. The locking ring is maintained in the locked position by a spring. When the locking ring is at the locked position, the balls get forced into the grooves they are aligned with, keeping the handle from rotating. When you pull the lock ring, there's an additional clearance above the balls and they are free to disengage and slide over the grooves, allowing rotation of the handle. I hope you found this video informative and interesting. If you did, don't forget to give it a thumbs up and subscribe.