Position Brakes vs Torque Brakes
Any torque arm can be equipped with several positioning brakes or with one torque brake.
The positioning brake or ‘drag brake’ holds the arm in one position so that it does not drift. They attach to each of the first and second axis of the arm. By applying some light pressure to the nutrunner or the end of the arm, you can overcome these brakes. Many torque arms are not equipped with positioning brakes at all, and are expected to drift away when the operator releases the nutrunner.
Positioning brakes are not meant to hold against a torque; they merely prevent arm drift.
Torque Brakes, on the other hand, are meant to withstand the torque exerted by the nutrunner. While it is theoretically possible to mount them on the second axis, typically they are mounted on the third.
There are two heavy caliper brakes and a disk brake in the photo below right. These brakes are normally off until the time the nutrunner begins to spin. Torque brakes will have a safety factor against slippage of about 2:1.
Torque brakes are generally air-operated and are much more powerful than positioning brakes. If a torque brake is not present when it should be, the arm will begin to turn unexpectedly when torque is applied, possibly resulting in injury.
When do I need a torque brake?
Usually, torque brakes are only needed when the fasteners to be tightened are vertical (or semi-vertical) and the nutrunner must be repositioned at the third axis.
Example 1: All fasteners are horizontal: typically, no torque brake is required because the arm geometry withstands the torque.
Example 2: All fasteners are vertical and the nutrunner has an in-line shape. There is no reason to spin or reposition the nutrunner at the end of the arm and no torque brake is required. The nutrunner can be fixed at the end of the arm and the arm geometry withstands the torque.
Example 3: Several fasteners are significantly off vertical (but are not horizontal) and are arranged in a long row. In this case, the nutrunner has to be twisted slightly with respect to the arm as each fastener is engaged and a torque brake at the third axis is required.
Example 4: All fasteners are vertical and arranged around the perimeter of a hub. The nutrunner has a right-angle shape. The operator must reposition the nutrunner at the third axis with each fastener to avoid interfering with the hub, and a torque brake is required.
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