Torque wrenches are used for tightening the bolts on any structure or mechanical assembly, whether it is of a car or other device. Engineers have designed the bolts and nuts on your car or device to take a particular load. So a bolt or nut has to be tightened just enough so that it allows the assembly to function to the load that it is designed for. Over tightening of a bolt or nut could damage the threads and thus render the fastening device defective. A damaged thread will not function as it is supposed to, and this could cause the assembly to function in a dangerous way.
Engineers have designed a wrench known as a torque wrench which will allow you to tighten the nut on a bolt to the required extent so that the assembly functions properly. This wrench would have a dial which allows you to set the pressure to which you want to tighten a nut. Once this pressure is achieved the torque wrench would give an indication or reading on the dial. Some wrenches give a click so that you stop tightening the nut further.
Setting the Torque Wrench
A torque wrench has a dial at one end which allows you to set the required pressure for the tightening of a nut. You would have to obtain the required pressure from the manufacturer’s manual of the device you are assembling to know the settings to which you have to put on the dial of the torque wrench. If you do not have such a manual you can find recommended settings on the Internet and use them as a guide line. If your torque wrench has only a dial indicating the pressure you would need to watch it carefully to see that you do not exceed the required pressure. If you have the click type, the wrench itself will give you the indication for you to stop the tightening.
Tightening Nuts with a Torque Wrench
Nuts for any assembly should not be tightened at one go. It is better to do the job in steps, at least three and move from 50 percent tight to 75 percent tight and then finally to the figure recommended.
Most assemblies would have more than one nut holding it together. When there is more than one nut involved tighten all the nuts for the first step of 50 percent, then again do all the nuts to seventy five percent and then all of them to the final hundred percent. This is necessary so that the assembly fits correctly, as if you tighten one side first, the assembly may not fit snugly and cause some problems later on in the function. Where gaskets are involved, it could cause a leak opposite the side which has been tightened to the full value first without using the other nuts. Follow the criss-cross pattern when starting with the assembly and tightening the nuts.
Once the nuts have all been tightened to the required pressure do not try to tighten them further. People have a tendency to give a last final tightening on a nut before they consider the job complete, quite often leaning on the wrench with one’s full body weight. If you are not too sure, reset your torque wrench and then check again to see if the nuts have been correctly tightened.
While tightening a nut, apply a smooth pressure on the wrench and avoid jerking it as this could upset the setting and cause your wrench to indicate completion before it has actually been achieved.
Caring for a Torque Wrench
A torque wrench is a precision tool and needs to be handled carefully. Before you put away a torque wrench set it to zero. If you are having any doubts about your torque wrench have it professionally recalibrated so that you are sure of the settings.