Type of Torque WrenchesThe torque wrench is a specially calibrated tool that, used to accurately tighten a fastener to a given torque. The torque wrench measures the amount of twisting force applied to the nut, bolt or screw that is being fastened. The wrench will be equipped with either a scale or dial attached which shows the applied pressure, featured on the rigid & flexible beam type torque wrenches. Ratchet or snap type torque wrenches have a ratcheting mechanism that releases or “snaps” when the selected pressure has been reached.
Flexible Beam Wrench
Flexible beam wrenches are easy to operate because when pressure is applied to the handle of the wrench, the needle moves to the right or left which indicates the amount of pressure or torque being applied to the fastener. When the pressure is removed, the needle will automatically return to zero. The pivoted handle focuses the applied turning force at the precise point on the lever to ensure the accuracy of the torque. This wrench can either be used in the left or right hand directions. Accuracy is +/- 2%.
How to use a Flexible Beam torque wrench
Install the proper size socket on the drive end of the torque wrench.
Attach the socket to the fastener that needs to be tightened. If necessary, hold the head of the bolt with the appropriate size wrench.
While keeping the direction of pull at right angles to the handle, pull the wrench with a smooth and steady motion. Make sure you apply the force to the center of the handle. If the handle is equipped with a pivot point, apply equal force to keep the handle centered on the pivot point.
Tighten the bolt until the scale reaches the required torque.
Dial Type Torque Wrench
This wrench gets its name for the easy to read torque measurement dial attached to the wrench and allows the operator to quickly identify the torque that is being applied. The torque is measured by a needle that moves inside a dial and can be used in both right and left directions.
How to use a Dial Type torque wrench
The first three steps used for the flexible beam torque wrench are the same for the dial type torque wrench.
Turn the bolt until the reading on the wrench matches the required torque value.
Ratcheting or Snap Type Torque Wrench
When using this type of wrench, the required torque is determined before the wrench is used by turning the micrometer, located above the handle, to the desired setting on the shaft of the torque wrench. When the pre-set torque is reached a click can be felt and heard. Most of these wrenches are designed for use in only one direction (either clockwise or counter-clockwise).
How to use a Snap Type torque wrench
Unlock the handle and adjust it to the necessary scale position for the required torque, then lock the handle. Apply pressure in a steady and smooth motion. When the wrench reaches the set torque the handle will automatically release or snap.
Follow the maintenance manual
Always follow the maintenance manual’s procedures for torque wrench use. The manual needs to be followed carefully because it will contain information on torquing techniques, standard practices in using a torque wrench and standard torque value tables.When the torque value for a particular fastener or fitting is not specified in the maintenance manual procedures, the mechanic should use the torque values listed in the maintenance manual’s standard torque tables.
Select the proper torque wrench
Select a torque wrench that has the required torque to be applied falling around the middle or well within the wrench’s high-low torque range. Make sure the selected wrench’s capacity is rated above the torque required. Never exceed or go below the torque value range of the torque wrench. Don’t ever use a torque wrench as a breaker bar to loosen nuts or bolts.
Before using any torque wrench, make sure it has been calibrated and that its calibration date has not expired. The torque wrench will have a sticker that lists the last calibration date and the next calibration due date. Don’t use a torque wrench if the calibration sticker is missing or expired.Torque wrenches must be calibrated at least once a year and they need to be tested for accuracy at least once a month. Some companies require that you check the accuracy of the torque wrench before each use by comparing its reading to a calibrated torque pendulum. If the wrench is dropped or damaged in service, return it to the tool room for re-calibration or repair. Never use your own personal torque wrench unless its calibration requirements satisfy FAA and Airline requirements if permitted at all.
Units of measurementAlways know the units of measure the torque wrench you select uses. As long as the required torque falls well within the torque value range of the wrench, you can use either inch-pound or foot-pound torque wrenches. You will just need to convert the required torque to the proper units of the wrench if the required torque is not given in the units of the torque wrench you are using. Foot-pound torque wrenches are usually only used for larger torques.
Torque nuts & bolts with clean and dry threads
Unless otherwise specified in the maintenance manual, always make sure that the nut or bolt you plan to torque has clean and dry threads. In some engine manuals it specifies that thread lubricant shall be applied to all engine parts which are to be torqued unless otherwise specified.
Always use a backup wrench when tightening a nut onto a bolt or when tightening couplings and bulkhead style fittings. Back the fitting and torque the nut in all cases.
Unless otherwise specified by the maintenance manual. When you are given a torque range, for example of 60 to 80 inch-pounds, torque on a specific fastener do the following:
Torque to the midpoint of the torque range (in this case torque to 70 inch-pounds).
If you have to torque the bolt head of a nut-bolt combination instead of the nut because the nut isn’t accessible, tighten it to the upper limit of the torque range (in this case 80 inch-pounds).
If you are torquing a castellated nut, torque to the low end of the torque range (in this case 60 inch-pounds), and then check if the castle cut-out on the nut is aligned with the hole in the bolt shank to allow for the insertion of a cotter pin. If they don’t align, tighten the nut until they do but in no case is the maximum torque of the range to be exceeded. If the alignment can’t be accomplished without exceeding the maximum torque it may be necessary to select a different length bolt or to add washers (a maximum of 2 under the nut and or bolt head).
Applying torque to a fastener
Apply torque with a slow, smooth and uniformed pull at right angles to the torque wrench handle.
Tighten the nut-bolt combination or bolt until it just begins to connect the component, washer or bearing surface. As you do this, check the torque required to turn the bolt into the hole or for the nut to be turned onto the bolt. This is known as the friction drag torque. It is basically a measure of how much torque is needed to screw a nut (especially a self-locking nut) onto a bolt or to screw a bolt into a hole. This measurement must be done before the nut or bolt contacts the component or structure. This friction must be added to the desired torque to get a final torque for the fastener. This final torque is the one to be indicated on the torque wrench.
Using the torque wrench, tighten the nut or bolt to its required final torque. For accurate torquing, the final turn of the nut or bolt must be made with the torque wrench.
Re-check the torque on the fastener.
Applying torque to multiple fasteners in sequence
When there are several bolts to tighten on a component (especially when they are arranged in a circle) they must be tightened in a specific sequence that is usually specified in the manual. If it isn’t specified, torque the bolts 180 degrees apart.
Tighten each bolt until it just begins to contact the structure.
Tighten each bolt to half it’s torque value following the proper sequence.
Tighten each bolt to it’s final torque following the proper sequence.
Re-check the torque on each fastener.
A L + E L = Lever length of the torque wrench.
E = Length of the extension.
T = Required torque on nut or bolt.
A = Distance through which force is applied (= L + E ).Example: A nut requires 180 foot-pounds of torque. You are using a 12 inch long torque wrench with a three inch extension. What should the torque wrench dial read in order to provide 180 foot-pounds of torque? R= L x T = 180 x 12 = 144 foot-pounds. L + E 15 See more of our How To Guides