By Scott Bittler
Understanding fastener torque and the corresponding values is important when working on aerial devices and digger derricks. There are critical fasteners that require periodic torque checks to verify the fasteners are uniformly loaded, not just a “by feel” or a visual inspection. Sometimes it’s not easy to access a bolt that needs to be torqued to a specific value on a piece of equipment. When other components are in the way, mechanics may be faced with disassembling equipment or using some kind of torque wrench adapter to get a better angle. A torque wrench adapter can help you work smarter, not harder, as long as you do so correctly.
FIGURE 1: Examples of items that can affect the torque applied to the fastener
It would be a misperception that if you are using an extension between the socket and the torque wrench that you automatically have to adjust for torque values, or worse, that an adapter does not require adjusting the torque wrench setting. It is true you must adjust the torque wrench setting if the pivot point distance to the direction of application of force on the torque wrench is affected; it is not true if only an extension with no adapter (in most cases) is used. Here’s why: The further away the fastener to be torqued is from the torque wrench pivot point, the less force it takes to apply the required torque on the fastener.
In the picture above, an extension with a swivel and socket can affect the torque depending on the angle. Adapters will affect the torque wrench setting if the distance changes between the fastener and the torque wrench handle. A straight extension will have no effect on the torque wrench setting.
Terex Utilities provides Tech Tips on its website to provide additional insight into frequently asked questions our service representatives receive. The following information is taken from Tech Tip #53. For more information, visit www.terex.com/utilities, click on Support, then choose Tech Tips. Tech Tip #53. It can be found under Auger Drill, Digger Derrick or any Aerial Device product category.
FIGURE 2: In this orientation of adapter to wrench, NO adjustment is needed.
Don’t Over Torque
Of the items that can affect the torque applied to the fastener (see Figure 1), straight extension used between the socket and the torque wrench do not affect the torque wrench setting.
Any adapter or offset that changes the distance between the centerline of the fastener and the centerline of the torque wrench drive will require an adjustment to the setting of the torque wrench. If no adjustment is made, the fastener will not have the correct torque applied.
The formula to adjust your torque wrench setting is:
Setting = (torque wrench length x torque desired) ÷ (torque wrench length + adapter extension length)
Step 1: Determine the adapter extension length or offset of fastener to torque wrench by measuring the distance between the following centers. The length of the torque adapter in this example is 3 inches.
Step 2: Measure your torque wrench length from the center of rotation to the center of the handle. Some wrenches have a mark on the handle for reference. If no reference mark is present on the torque wrench, mark the center of the handle area for measurement. The length of the torque wrench in this example is 18.5 inches.
Step 3: (torque wrench length x torque desired) = (18.5x180) = 3,330
Divide this by (torque wrench length + adapter extension length) = (18.5+3) = 21.5 inches
3330 ÷ 21.5 = 155 ft. lbs.
A torque wrench setting of 155 ft. lbs. is needed to adjust for the 3-inch torque adapter being used to get a torque value of 180 ft. lbs.
Summary: 155 ft. lbs. = (18.5 inches x 180 ft. lbs.) / (18.5 inches + 3 inches)
Additional examples are available online in Tech Tip #53.
Best Practices for Maintaining Torque Values
Critical fasteners, such as those found on the rotation bearing of aerial devices and digger derricks, often require mechanics to check the torque of bolts every six months. While every piece of equipment will have its own list of critical fasteners, users are more likely to keep up with manufacturer’s recommendations if the bolts are easy to access. During equipment design, Terex Utilities pays special attention to accessibility of fasteners for maintenance purposes, but space constraints may prevent easy access. This does not relieve the technician from the responsibility of inspecting all fasteners that require torque checks. For example, the new Optima Series of Hi-Ranger aerial devices feature a new pedestal design that provides technicians easier access when inspecting and torqueing lower rotation bearing bolts, which are now accessible on the outside of the pedestal. But when that’s not the case, making good use of a torque adapter makes proper inspection and maintenance easier. The best practices presented here apply to any bolt that must be torqued to a set value. UP
FIGURE 3: In this orientation, adjustment is required.
About the author: Scott Bittler is a National Service Trainer and Technician for Terex Utilities. He has more than 25 years of experience in shop and field service, and is an NCCCO certified digger derrick operator and practical examiner.