Mechanics depend on torque wrenches to have precise and consistent torque measurements such that the correct amount of force can be applied to the nuts and bolts in the vehicle.
Nonetheless, torque wrenches need to be adjusted periodically to ensure correct readings are given. Although it might be better to take your torque wrench to a qualified car mechanic, you can do a fairly decent job of holding your torque wrench correct by calibrating it at home.
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What is torque wrench calibration?
Calibration is a measure that defines the accuracy of precise tools like torque wrenches. This parameter is typically checked in torque wrenches and similar tools where accuracy is the most essential factor. The calculation of the physical force applied by the torque wrench is calculated and compared to its fixed torque value. In such a way, you may define the accuracy of a certain torque wrench range permitted by the International Organization for Standardization (the short is ISO).
For general, the ISO standard requires 4 to 6 percent above or below the torque range shown by the setting of the torque wrench while measuring. Although everything above such limits is deemed to be non-compliant. To test if a torque tool is not calibrated, you may need the help of professional and special equipment.
How to do testing of torque wrench calibration:
1) You should do the measurement starting from the square drive head and follow the instrument to the handle
The square drive is the ending point of any wrench to which you can mount the plug. Using entire inches instead of using the percentages for convenience. Label the stage you calculated to the handle and document the distance on a sheet of paper to bring you back to later. Set the document aside in a quiet position before you use it. Because 24 inches is a typical length for most torque wrenches, it will serve as a guide for further moves.
2) Make sure the square drive head is secured in the bench vice
Align the bench vice so that you can put the square drive of the instrument in and stretch the handle far away from the bench or desktop. Then put the square drive into the vice and keep it until it’s safe. Be cautious not to overtighten the vice and harm the square drive head. The square-drive head has to be trapped in the lock so that the wrench will shift under the weight that you add while measuring the torque range.
3) You should calculate the appropriate settings, according to the chosen weight
To decide the proper setting for the torque wrench, subtract the gap you calculated during the second step by 20 pounds that you would need for your weight. The torque range is 480 inch-pounds (24 inches x 20 pounds) which is equal to 40 ft-lbs. Be sure to use the appropriate distance and weight details. If the tool is small in scale or whether you select various weights, the numbers would be smaller.
4) The weights should be hung from the tool’s handle
Attach the rope to the weight. Create a loop that you can keep from the handle of the tool (check step 1). Be sure that the length of the rope is sufficient enough to keep the weight from hitting the ground until you hang it. Do not bind the weight to the wrench firmly. Instead, just keep it. Don’t make sure that nothing is in the path of or helping the weight while it falls.
Where to get a professional calibration for any torque wrench?
The best place to have a torque wrench equipped is a special torque testing laboratory capable of managing any form of torque device, including a torque multiplier, of up to 35.000 pounds per foot of applied force and a torque transducer that can weigh up to 20.000 pounds per foot.
This form of full-service torque adjustment and repair is fairly uncommon, although certain torque tool manufacturers do not only sell the wrenches but also comply with the ISO 6789:2003 buying requirements and are both approved according to the ISO 9001 standard and certified with the ISO 17025 standard. The torque wrenches makers should provide the special calibration certifications, especially if they sell professional equipment for auto repair shops.
How to do DIY calibration for a torque wrench?
If you are absolutely sure about what to do, make sure to follow these steps. If you have never calibrated a wrench in-house, then it is better to let experts do the calibration.
The things required for DIY calibration for torque wrenches:
- Click-style torque wrenches;
- Paint pen or markers;
- Tape measure;
- Any 20-to-35 pound weight;
- A rope to hand this weight;
- A lug nut attached to any non-important equipment;
- Anything to record the calculations – a smartphone or a paper notebook;
- The boots or shoes with the safety for toes;
This is what you need to bear in mind when calibrating a torque wrench:
The measurements should be captured
When testing the wrench, always calculate from the middle of the square drive where the plug is connected. Mark the handle where you end the calculation. You may want to use a permanent black marker.
The example: to calibrate an 18-inch torque wrench, the standard length of a torque wrench, and place the mark at 15 inches, which is the desired distance for a single increment. It is better to record each stage of the calibration to avoid any miscalculations.
You should secure the wrench
This move fits well if you’ve got a target to put your tool in. If there is no lock, place the socket on the wrench and put the socket and then the tool on the lug nut of your vehicle part. Leave some vertical room to add the rope and the weight to do the calibration check properly.
Face the handle externally so that the bench doesn’t obstruct the rope and the weight. Make sure that the square drive is the only item clamped in your aim so that the handle can shift without restrictions. If you do on a piece of the device, place the carton behind the wrench so that you do not inadvertently harm the body of the machinery by the weight of the chain. That is why you need to wear safety-toe shoes in the case of dropping the wrench on the feet.
Do the math
To get the right setting for your instrument, you would need to subtract the gap from stage one by the weight you use to get the inch-pounds. For instance, you may take a 20-pound weight. Then divide that amount by 10, which will give you the range in foot-pounds. Bear in mind that whether you use specific ratios or distances, the number could vary.
The calculations can be done even without a calculating device:
- 20 inches x 20 pounds = 400 inch-pounds;
- 400 inch-pounds / 10 = 40 foot-pounds;
So, the torque range of the calibrated tool is 400 ft-lbs.
Double-check the calibration after securing the weight:
- Secure the cord or chain about your weight;
- Create a loop at the other end that is wide enough to comfortably slip over the torque wrench. Make sure the cord is long to the extent that the weight does not reach the ground;
- You need to set the tool to the scale of 25 ft-lbs;
- Hang the end of the cord on your instrument where you found the ending point during the 1st step (15 inches). The weight is now suspended;
If your wrench has pressed once, the weight has been added, then adjust it to 26 ft-lbs. If you haven’t pressed, the instrument is already reliable to use.
Adjust the calibrated tool
You should change the torque range and accuracy for your wrenches by adjusting the tension spring. These springs could be found in the center of the tool or under the shaft, which would take a bit more testing to be completed.
You may need to alter your proportions to shift your weight as the mark falls on the fixed screw location. Make sure the instrument is already calibrated to the foot-pounds (check the step 3). Do the following steps:
- Hang the end of your rope with the weight – check the step 1 as well. This step could be different if you had to cut the handle to reach the screw set;
- If you haven’t felt it turn (the click sound), you may need to lift the weight and adjust the screw in the clockwise direction in tiny intervals called increments;
- Hang the loop end of the rope with your weight back on the mark on the tool and then press again to check whether the measurement was appropriate. If you don’t feel the click, you’ll need to keep doing this cycle;
- After you’ve felt a sound, lift the weight and re-attach the handle (if you had to drop it to adjust);
Now the tool has been checked and adjusted, so you should feel confident adding the correct amount of torque. If you can’t change your instrument using such tools, give it to a specialist or buy a new tool.
Tips for maintaining the calibration of torque wrenches
So you’ve spent money or your time for the calibration of your torque wrenches, or maybe you have already bought the pre-calibrated tool. In all these cases, you may want to keep the wrench calibrated as long as possible. Here is how you should maintain the calibration of the tools:
- After each use, you should return the scale to zero to prevent the poor calibration while the wrench is stored. For instance, the internal spring may cause the drift of the tool’s calibration.
- Do not drop or let the calibrated wrench fall. Dropping (as well as using the wrench instead of a hammer) the tool onto any hard surface will definitely affect the accuracy of calibration;
- Use the calibrated wrench only for fastening or loosening the bolts, according to the manual. For instance, some mechanics also use these wrenches as breaker bars but it could result in poor calibration;
- Do not exceed the maximum and minimum limits of a wrench. Otherwise, the tool may snap or its calibration could be affected;
- It is recommended to store the calibrated torque wrenches only in their cases or apart from other tools (not in the common compartment with other tools). Most premium torque wrenches include the protective cases by default;
- Calibration also heavily depends on any strong impact, humidity and low/high temperature changes. That is why it would be preferred to store the calibrated wrenches in the area with regulated climate control.
As you might have guessed, calibration is one of the most important factors to check before buying a torque wrench. Consider choosing the wrenches with pre-calibration at the manufacturer’s factory, according to ISO standards. Only these top-notch tools won’t let you down when fastening or loosening the bolts/screws/nuts.