What purpose do gimbals serve in torsionally rigid line shafts?

By Zak Khan

Line shafts transmit motion in systems over long distances. But to do so, they must have support along their lengths. A specific kind of line shaft, torsionally rigid line shafts, have unique properties that allow them to work with supports that function with the aid of gimbals.

Torsionally rigid line shafts are shafts that remain rigid in the face of torsional, or twisting, forces. This allows them to handle much more misalignment than other shafts as a factor of how long they are. They are usually built out of flexible bellows couplings, clamping hubs, and the shaft tubing itself, which is usually aluminum, steel, or carbon fiber. Of these, carbon fiber is best used for longer lengths of line shafts.

Gimbals are supports that allow the rotation of what it is supporting around one axis. As an example, gyroscopes use multiple gimbals to remain upright. In torsionally rigid line shafts, gimbals inside the shaft ends allow the end supports to hold the weight of the long tube section of the shaft. This is important because it allows engineers to avoid using external shaft supports at periodic intervals along the run of the line shaft.

Gimbals also aid in system design because they prevent the maximum deflection allowed in a system from being exceeded. This adds to the safety of a line shaft system. Because there is only one axis in which the line shaft can move, the rotational axis, and the bellows coupling fails, the shaft tubing can spin down to a rest and not damage other components in the system.

These combinations of characteristics allow engineers to use gimbals in torsionally rigid line shafts. Manufacturers provide documentation on how long shafts can extend with no support, often this can reach nearly 20 feet. Consult relevant information for specifics and always consult with manufacturers.