How to Calibrate a Torque Wrench
Every professional and amateur auto mechanic or worker should know the basics of how to calibrate a torque wrench. A good wrench calibration system is crucial to making sure that you don't over or undertighten the bolts on your wheels, engine and many other parts of your car as well. Because a torque wrench is a delicate device, you'll need to go through a careful process to calibrate beam torque wrenches or other types of wrenches as well. Additionally, you'll need to be prepared to recalibrate the wrench periodically so as to be sure that the wrench maintains its level of power and the settings that you've adjusted it to. Read on for a guide on how to calibrate a basic torque wrench for use in automotive repair projects.
Step 1 - Gather Your Materials
You'll need the following materials for this project:
- Torque wrench
- Pencil and paper
- Bailing wire
- Weights of various amounts (5 lbs through 50 lbs is ideal)
Step 2 - Put the Wrench in the Vice
Clamp the wrench into the vice, being sure that only the square drive portion of the wrench is touching the vice. The square drive is the box shaped portion at the edge of the wrench. You'll need to keep all other portions of the wrench free for you to use to recalibrate the wrench. Rachet the wrench so that it is in a horizontal position relative to the vice that it's clamped into.
Step 3 - Locate the Center of the Square Drive
The center of the square drive is the point at which the two diagonal lines that cut across the corners of the square drive will intersect. If it helps to use a pencil and a ruler to mark on your torque wrench, do so. You'll next need to pick a distance in inches and measure it out from the center point of the square drive along the handle of the wrench. Select somewhere between 10 and 24 inches, if possible. The exact distance that you choose is irrelevant.
Step 4 - Select a Weight and Set the Wrench
Choose a weight that closely resembles the amount of force that you would place on the wrench handle (somewhere between 30 and 50 lbs is good). Multiply the distance in inches from the center of the square by the amount of weight in pounds. Set the wrench to this number.
Step 5 - Hang the Weight and Calibrate the Wrench
Hang the weight from the wrench using bailing wire at the distance that you've measured. Take note if the wrench clicks or not; if it does, stop there. If it doesn't, you'll have to remeasure the distance and rehang the weight. Be sure to keep track of the new distance. This is your calibration factor. The torque setting on the torque wrench is equal to the actual torque applied times the measured distance divided by the second measured distance.