Oldham couplings are constant velocity couplings used for connecting two parallel shafts that are close together and run at the same speed. They are composed of three parts: a center piece sandwiched in between two hubs. The two hubs of Oldham couplings are generally made out of steel, stainless steel or aluminum while the center component is usually a plastic material and rarely metal. Torque transmission is accomplished by interlocking the slots of the center piece with the drive tenons of the hubs. They fit together by snapping into place, which creates zero backlash.

Oldham couplings are flexible and designed for general
purpose use up to 4000 rotations per minute because they have few
disadvantages. Their only disadvantages are their limited angular
displacement of shafts and their need for lubrication. This type of
coupling allows less than half a degree of angular misalignment and
less than 0.005 inches of axial motion. The axial motion is limited by
the design of the coupling which cannot accommodate push-pull motion.
Because the center piece is essentially floating, both shafts must be
supported to keep the coupling from coming apart. Their advantages
include no velocity variation, high lateral misalignments, high torque
capacity and easy disassembly. Oldham couplings are widely used for CNC
machines, homokinetic transmission, servo or robotic machines, copy and
printing machines and instrumentation.
Oldham
couplings function when one hub, or disc, is coupled to the input,
while the other is coupled to the output and the center piece is joined
to the other two by a series of tongue and grooves. During operation,
the center element slides on a hub tenon to accommodate misalignment.
This eventually wears down the discs. Springs are often employed to
prevent this and worn discs are easily and inexpensively replaced.
There are many different kinds of flexible shaft couplings besides Oldham couplings. The bellows coupling
has two hubs and a thin walled metallic bellows and can accommodate all
three types of misalignment. Single beam couplings are usually made of
a single piece of aluminum and have a system of spiral cuts that allow
it to bend in order to accommodate angular misalignment. Multiple beam
couplings consist of two to three overlapping beams that address
problems of torsional rigidity. Jaw,
or spider, couplings consist of two metallic hubs, each with a set of
interlocking teeth, and a flexible rubber or plastic piece in the shape
of a star which fits between them. These couplings have zero backlash
and function well at high speeds but do not tolerate a great deal of
misalignment.