A common tool that is used by the aerospace technician is the torque wrench. The purpose of the wrench is to precisely place the required amount of torque or tightening of a nut on a bolt without under or over torquing the nut. It is a misconception that people believe that “the tighter the better” applies to all nut/bolt arrangements. That is not true. Over-tightening a nut can crush the gaskets underneath, warp the bold threads, or cause the nut to be difficult to remove. Under-tightening can result in the nut coming off at an inopportune time. Using a torque wrench, you ensure that the nut is at the proper torque that is required avoiding damage or breakage.
There are four major types of torque wrenches an aerospace technician can use: Flexible beam, Rigid frame with a dial indicator, preset or “clicker” torque, or digital.
Flexible beam is used by grasping the center of the handle, turning the nut until the needle points to the torque desired.
Rigid Frame torque wrenches use a dial indicator to read the torque being applied.
Preset or “Clicker” torque wrenches can be set to the desired torque and will “click” when the proper torque is reached. The unit showed above can be set for either english standard or metric.
Digital torque wrenches will show the torque being applied via a digital readout and some models will actually beep when you have achieved the torque desired.
When using a torque wrench, keep these things in mind:
- Select the proper wrench for the measurement being called for. If inch/lbs are called for, then you select a inch/lb wrench. If inch/grams are called for, then select a wrench that is measured in grams.
- Check the calibration date on the wrench. If it is outdated, return to logistics and get a wrench that is within the calibration date.
- Always test the torque wrench on a torque measuring device to ensure that it is still calibrated and reading accurately.
- Never jerk the wrench, but pull on it slowly keeping close eye on the torque being applied.
- Always set the wrench back to it’s lowest torque setting after use to ensure that the spring does not compress and end up with “memory.”
- Always handle torque wrenches with care. Do not drop them or bang them around. Return them to their foam case once finished.
Torque is determined by the formula:
Torque=force X distance
For example if a an engineering drawing requires a 120 lb inch pound torque for a specific nut and you have a 10 inch torque wrench, you would figure out the following:
120 inch/lb=force X 10 inches
120 inch/lb divided by 10 inches=force X 10 inches divided by 10 inches
or 120 inch/lb divided by 10 inches= force
Therefore you need 12 lbs of force to achieve 120 inch/lbs using a 10 inch torque wrench.
This formula is very useful in determining the torque required.
Some technicians have been known to alter the length of their torque wrench by adding an extender. If that is done, then the force required to achieve 120 inch/lb of torque is changed. Let’s look at the same problem again and assume the aerospace technician has decided to add a 15 inch extender on his wrench.
120 inch/lb=force X (10 inches (wrench length) + 15 inches (extension length))
120 inch/lb=force X 25 inches
120 inch/lb divided by 25 inches=force X 25 inches divided by 25 inches
120 inch/lb divided by 25 inches=force
Note the difference in force required! If you had not taken into account the added length of the wrench, you would have over torqued the nut possible resulting in damage to the aerospace hardware.
With good care and timely calibrations, your torque wrench should last and be an invaluable tool in your work.