The oldham coupling is a form of flexible coupling designed for applications that must be free from backlash. They are also increasingly being used as a replacement for straight jaw couplings. The oldham coupling consists of three discs. Two of the discs, typically made of aluminum or stainless steel, are connected to either side of the drive, while the third, made from one of several different plastics, is sandwiched in between with a tongue and groove design. The tongue and groove on one side is perpendicular to the tongue and groove on the other. Springs are often used to reduce the coupling’s backlash.
During operation the center disk slides on the tongues, or tenons, of each hub (which are orientated 90° apart) to transmit torque. While the couplings accommodate a small amount of angular and axial misalignment, they are especially useful in applications with parallel misalignment.
The oldham coupling features several other advantages including their compact size and potential for electrical isolation through the plastic center disk. The couplings may also act as a sort of fuse for a machine. If torque limits are exceeded the center disc of the coupling will break apart first, preventing torque transmission and potential damage to more costly machine components.