It is very important to have reliable work tools; some need special maintenance and adjustments. About once a year it is necessary to have the torque wrench calibrated by a professional, but in some cases you can do this yourself. This article teaches you how to do it.
Steps
Method 1 of 2: Calibrate the Weight
Step 1. Make a mark on the back of the wrench at the center of the tool head
Step 2. Measure the distance between the mark and where you place your hand when you normally use the key
Draw another line at that point and note the distance.
Step 3. Secure the square head of the tool in a bench vise, making sure that no other point on the wrench comes into contact with the jaws
Move the handle horizontally.
Step 4. Align torque values by distance by moving in 10kg increments
Step 5. Hang a 10 kg object on the tool, making sure it matches the marks you made in the first two steps
Step 6. If you hear a "click", slowly lift the sinker and carefully move it towards the head of the key until the sound stops
Make a mark at that point and repeat the process to make sure you have placed the weight correctly.
- If you do not hear any noise, move the object away from the head of the key until you hear the "click". Make a mark and repeat the experiment to verify that it is the right spot.
- You can draw a definitive mark after two or three checks.
Step 7. Measure the distance between the square head and the mark you just made
This is another data required for the calibration equation. To find the exact torque value, multiply the distance by 10 kg and the acceleration due to gravity.
Step 8. Use the formula Ta = Tsx (D1 / D2)
Insert the values you detected into this equation, remembering that Ta is the force applied, Ts is the key setting, D1 the distance you found in the second step and D2 the last distance you detected.
Step 9. Check the calculations several times and change the key settings accordingly
Step 10. Note that the important distance is the distance between the center of the head and where you hung the weight
The position of the hand does not matter in this case. The value obtained is expressed in newton per meter and refers to the moment of the arm (the latter is the portion of the tool between the center of the head and the point where you hung the 10 kg object).
- So, if you put 10kg ballast at 0.3m from the center of the key head, considering also the acceleration of gravity you are applying 10kg x 0.3m x 9.8m / s2= 29.4 N m at the end of the tool.
- If you hung the item 0.15m from the center of the key head, you get 0.15m x 10kg x 9.8m / s2= 14.7 N m. To obtain precise data, the handle of the instrument should be parallel to the floor during this procedure, taking into account that the weight of the key itself also "unloads" on the fulcrum of the key. If you don't have a scale to check the weight of the key, consider values of 1, 3 N m or 2, 6 N m.
Method 2 of 2: With a Dynamometer
Step 1. Secure the head of the wrench in a vise
Step 2. Attach a dynamometer 30cm from the center of the head
Step 3. Determine the value of the force applied to the gauge based on the wrench settings
Step 4. Calculate the percentage of error
Step 5. Repeat the above sequence with different settings to determine if the error is constant
Step 6. Apply the error percentage to the key scale
Advice
- Remember to lift the sinker from the key handle and always double check where the "click" appears or disappears, to get accurate values.
- If you have any doubts about your ability to calibrate the instrument with these procedures, consult a professional who has the right tools and knowledge for a precise job.
- The ballast must weigh exactly 10 kg.
