Threaded fasteners – for example, nuts and bolts – come with appropriate torque values that are designed by the manufacturer. Under tightening the fasteners does not offer the proper thread loading, while overtightening can cause your fastener to weaken, leading to premature breaking.
Allowing you to measure the tension or twist applied to the fasteners, a torque wrench ensures that you are using the ideal rotational force. However, torque wrenches do lose their accuracy over time.
Through torque wrench calibration, one can get the instrument back to accurate operation. This once per year activity can help you ensure that all the parts on your mountain bike are perfectly tightened. In this detailed guide, you will learn how to adjust a torque wrench.
How to Perform Torque Wrench Calibration
1. Gather the Necessary Tools
To calibrate your torque wrench, you will need the following tools:
- A paint pen or marker
- Tape measure
- A vice secured on a bench
- A 20-pound weight
- A string or rope that is capable of holding the 20-pound weight
- A blank paper for recording your calculations
2. Measure the Length from the Wrench’s Square Drive to Its Handle
The square drive is simply the end of your torque wrench to which you would attach a socket. To make your work easier, try to avoid fractions – use whole inches only.
Mark the point you measured on your handle and then record the obtained length on a piece of paper – you will come back to this length later. Since the majority of torque wrenches are 24 inches long, we will be using this length in the steps that follow.
3. Secure the Wrench’s Square Drive in a Vice
Orient the bench vice in a way that you can place the wrench’s square drive in and have its handle extend out, away from the bench or table. Insert the square drive into your bench vice and tighten the vice until the wrench is secured in place.
Be careful to avoid overtightening your vice – this can damage your square drive. Ensure that only the square drive is caught in the vice’s clamp so that the torque wrench can move under the weight you will be applying.
4. Calculate the Ideal Setting for the Weight
In this guide, we will be using a 20-pound weight. To figure out the ideal setting for your torque wrench, multiply the length you recorded in step 2 by the 20 pounds. For our case, the length was 24 inches. Hence, our calculation will give 24 x 20 = 480 inch-pounds, which equates to 40 foot-pounds (Note: divide the inch-pound value by 12 to convert it to foot-pounds). After performing this calculation, set the torque wrench to 40 foot-pounds.
When performing the calculation, be sure to correct the weight and distance figures. If your bike torque wrench has a different length or you are using different weights, the figures you use in the calculation will be different. Set your torque wrench to the obtained figure – for example, since we obtained 40 foot-pounds from our calculation, our torque wrench will be set at 40 foot-pounds.
5. Hang the Weight from the Wrench’s Handle
Tie a good rope to your weight. Be sure to use the right knots to make a loop that can hang from the wrench’s handle. Be sure to hang the weight on the mark you had put on the handle in step 2. Ensure that the length of your rope is short enough to keep the weight from touching the ground once you hang it.
Avoid tying the weight securely to the torque wrench – instead, simply hang it. Double-check to make sure that nothing is supporting or in the way of the weight.
6. Use the Weight to Adjust Your Torque Wrench
You can adjust the spring tension in the torque wrench by turning a screw usually located midway up the handle using a screwdriver. After hanging the weight as explained in step 5 above, see if it clicks. If your torque wrench clicks, then it is properly calibrated.
If it does not click, you can do torque wrench calibration by simply turning the screw clockwise to tighten the spring. Once you do this, lift your weight and lower it to test.
Repeat this process until your wrench clicks using the known weight – this should be the proper calibration. If you are new to how to adjust a torque wrench, it is easy to forget to lift the weight after each adjustment – if you forget, you won’t be calibrating your wrench correctly.
7. Move the Weight Up the Wrench’s Handle
Once you hear the click, the next step on how to adjust a torque wrench is to move the weight up the wrench’s handle. Simply lift the weight and set it down further up your wrench’s neck, moving toward the wrench’s head.
Repeat this process until you can’t hear the click. Avoid sliding the weight up the handle – instead, lift it and set it down each time.
8. Start Moving Away from the Wrench’s Head
If you have followed step 7 above to the point where you can’t hear a click anymore, you will need to move the weight down the handle (away from the head) until you hear the click.
You can start by moving the weight about an inch at a time. You can move the weight up and down the wrench’s handle as you try to locate the position where it starts clicking – while this can take some time, it will make the wrench more accurate for your next bike maintenance job.
Once you locate the point where the handle transitions from not clicking to clicking, use a pen to mark it. The point where the torque wrench stops or begins clicking is known as the transition point.
9. Measure from the Wrench’s Square Drive to the Transition Point
Record the obtained length on a piece of paper. To show you how to adjust a torque wrench, we will use 26 inches as an example. However, keep in mind that your length might be different. Be careful to avoid confusing this number with the length you had recorded in step 2.
10. Calculate the Applied Torque
If the transition point on your torque wrench for 20 pounds was at 26 inches, multiply the length with 20 pounds to figure out the torque applied. For our case, the value will be 20 pounds x 26 inches = 520 inch-pounds.
11. Correct for the identified Difference
If for any reason, you are unable to perform the torque wrench calibration fully, you can still use it on your road bike or commuter bike accurately by adjusting the settings you use on the wrench to compensate for the difference.
To do this, you will need to divide your first measurement by the transition point – for our case, 24 inches divided by 26 inches, which gives 0.923. Whenever you need to use your torque wrench, for example, when changing your bike tire, always multiply the correct torque by this number.
By multiplying the intended torque with the difference, you will be able to get the correct setting for the torque wrench. This solution can allow you to keep working. However, the torque wrench will still need calibration.
How to Maintain the New Torque Wrench Calibration
After calibrating your torque wrench, you will need to do everything in your power to ensure that the wrench offers accurate readings for as long as possible. The tips outlined below can help you with this:
1. Return Your Scale to Zero After Use
After using the torque wrench, for example, to replace your bike cassette or to simply adjust bike gears, always remember to return its setting to zero. If not left in zero, the strain on the torque wrench internal spring can cause your calibration to drift.
2. Maintain a Tight Grip on Your Torque Wrench
Dropping the torque wrench onto a hard surface will affect the tool’s calibration. Always set down the torque wrench in safe places where it cannot fall.
Also, avoid using the torque wrench in areas where you out to be using a hammer. Banging the torque wrench will not just affect its calibration, it may also break it.
3. Use Your Torque Wrench for Appropriate Tasks
Torque wrenches are similar to breaker bars. For this reason, people often assume that it is okay to use the 2 interchangeably.
You should only use your torque wrench in situations where specific torque specifications are needed. Using the tool for other jobs will affect its calibration.
4. Stay Within the Tool’s Lower and Upper Limits
Whether you are changing a bike wheel, replacing the bike pedals, or working on a task that requires a lot of energy input, you should always be careful to avoid exceeding the prescribed limits for your torque wrench. In addition to affecting the calibration, exceeding the limits can damage your tool.
Most torque wrenches will come with the lower and upper torque tolerance indicated on them. Avoid using the torque wrench for jobs that require more than the indicated tolerance.
5. Store the Torque Wrench by Itself in Its Case
Since the torque wrench can be affected by various impacts, including temperature changes, you must store it away from your bike multitools and other maintenance gear. Keep the torque wrench in its protective case.
If possible, keep the tool in a weather-controlled area, since big humidity and temperature shifts can affect the calibration. Keep the torque wrench low so that it does not get affected by falls.
Q: How Do You Calibrate A Torque Wrench?
When calibrating a torque wrench, you will need to hang a specific weight on a pre-identified position and then turn a screw located midway up the wrench’s handle until you hear a click. Make sure that the wrench is set at a torque obtained by multiplying the weight and the distance from the square drive to where you are hanging your weight.
Q: How Often Should A Torque Wrench Be Calibrated?
The torque wrench should be calibrated after every 12 months or 5,000 cycles. Since keeping track of the cycles can be difficult, calibrating the torque wrench once per year may be a good idea.
Q: How Much Does It Cost to Calibrate A Torque Wrench?
Torque wrench calibration can cost anywhere from $50 to over $500. Things like wrench capacity and the lab performing the calibration will affect the cost. Wrenches featuring high capacities will cost more to calibrate and labs featuring a high ISO accreditation will require more money to calibrate your torque wrench.
Q: Do You Have to Calibrate Digital Torque Wrench?
All torque wrenches do lose their calibration over time. Hence, if you have used your digital torque wrench for 12 months or 5000 cycles, you should consider calibrating it.
Q: Where Can I Calibrate A Torque Wrench?
The best place to calibrate your torque wrench is in a torque calibration laboratory. Look for a lab that is capable of handling all types of torque tools.
Q: Does a Torque Wrench Need Calibration?
With time, torque wrenches will lose their calibration and start giving inaccurate readings. The best way to get the wrench back to operating normally is to invest in calibration. If you have time, you can always calibrate the torque at home by following the steps outlined in this guide.
Globo Surf Overview
One of the most important tools in car and bike tool kits, torque wrenches play a significant role in maintenance jobs. They will help you avoid exceeding the force needed for different bolts and nuts on your car or budget road bike.
However, if the torque wrench hasn’t been calibrated in a long time, its readings will be inaccurate. This is why performing torque calibration after 5000 cycles or every 12 months is extremely important. This article shows you how to adjust a torque wrench. With the steps above, you can avoid spending your money on calibration labs.