If you have ever tried to connect two shafts that are not perfectly aligned — and in the real world, they almost never are — you quickly discover that a rigid connection is not a solution. Rigid couplings transmit misalignment forces directly into the shafts and their supporting bearings, causing accelerated wear, vibration, and eventually premature failure. The Oldham coupling exists to solve exactly this problem, and it does so through a mechanism that is as elegant as it is effective.
This guide explains in plain engineering terms how an Oldham coupling works, what happens inside the coupling during operation, how it compensates for lateral shaft misalignment, and what its practical limits are.
Every Oldham coupling consists of exactly three parts: two identical outer hubs and one centre disc. This simplicity is intentional — there are no springs, no elastomeric elements, and no lubrication passages that can fail or degrade.
The two outer hubs are typically machined from aluminium alloy or stainless steel. Each hub has a bore that clamps onto its respective shaft using a set screw or a split-clamp arrangement. On the face of each hub, a single rectangular slot (or a raised tenon, depending on the design convention) is precisely machined. The critical geometric fact is that the slot on the driving hub and the slot on the driven hub are oriented at exactly 90 degrees to each other.
The centre disc — also called the slider, insert, or tongue disc — has a raised tenon on each face. These tenons are also perpendicular to each other, matching the slot geometry on the hubs. When the assembly is complete, each tenon sits inside a hub slot, and the disc is sandwiched between the two hubs, free to slide laterally but rotationally locked to both.
When the driving shaft rotates, the driving hub rotates with it. The hub’s slot engages the tenon on one face of the centre disc, pushing the disc rotationally. The disc, now rotating, engages the tenon on its other face into the driven hub’s slot, causing the driven hub and its shaft to rotate at the same speed and in the same direction.
The torque path is therefore: driving shaft → driving hub slot → centre disc tenon (face 1) → centre disc body → centre disc tenon (face 2) → driven hub slot → driven shaft.
At every point in this chain, the connection is a positive form-fit — a solid surface pushing against another solid surface. There is no compression of an elastomeric element and no angular free play. This is why Oldham couplings are classified as zero-backlash devices: the direction of torque transmission reverses instantly without any dead band.
This is the mechanism that makes the Oldham coupling truly unique. Lateral misalignment — also called parallel offset — occurs when the centrelines of the two shafts are parallel to each other but separated by a distance in the radial direction. This is extremely common in real machinery where perfect coaxial alignment is difficult to achieve and maintain.
Here is what happens inside the Oldham coupling when the two shafts have a lateral offset:
Step 1: As the driving hub rotates, its centre traces a circular path around the driving shaft axis.
Step 2: The centre disc is constrained to slide along one axis relative to the driving hub (the hub slot allows sliding in only one direction). As the hub rotates, it pushes the disc, which slides back and forth within the hub slot in a reciprocating linear motion.
Step 3: Simultaneously, the driven hub is constrained to slide along the perpendicular axis relative to the centre disc. As the centre disc oscillates, it drives the driven hub, which itself slides back and forth in the perpendicular direction.
The net result is that the centre disc performs a simple circular orbit between the two hubs — tracing a circle whose diameter equals twice the lateral offset between the shafts. This orbital motion fully absorbs the offset without transmitting any radial force onto the shaft bearings. The lateral misalignment is accommodated entirely by the sliding motion of the disc within the hub slots.
This is the key insight: while the disc moves, the shafts themselves rotate smoothly about their own axes. The coupling acts as a kinematic bridge between two non-coaxial rotation centres, transferring torque faithfully while allowing the offset to exist without creating destructive reaction forces.
This is a question that engineers sometimes overlook, and the answer is nuanced. When the two shaft axes are perfectly coaxial (zero offset), the Oldham coupling transmits rotation at a constant 1:1 speed ratio with no velocity fluctuation.
When lateral offset is present, the output velocity is theoretically constant in a true kinematic Oldham coupling. This is because the mechanism is a constant-velocity (CV) joint for parallel offset — a property it shares with only a few other coupling types. At any given input angle, the output angle is identical, and the angular velocity ratio remains exactly 1:1 throughout the full rotation.
This constant velocity property is one reason the Oldham coupling is preferred over a double-Hooke’s joint (double cardan joint) in precision applications requiring parallel offset compensation. The Hooke’s joint inherently produces a sinusoidal velocity fluctuation, while the Oldham coupling does not.
Understanding the coupling’s capabilities requires distinguishing between the three fundamental types of shaft misalignment:
Lateral (parallel) offset: The Oldham coupling’s primary design function. It can typically accommodate between 0.2 mm and 2.0 mm of parallel offset, depending on the coupling size. Some large industrial variants handle even greater offsets. This is the misalignment type the coupling handles with zero additional bearing load and no velocity distortion.
Angular misalignment: An Oldham coupling is not designed for angular misalignment — the condition where the two shaft centrelines are not parallel to each other. Its theoretical angular capacity is close to zero; in practice, manufacturers typically specify a maximum of 0.5 to 1.0 degrees. Exceeding this causes binding in the hub slots and introduces undesirable axial forces. For angular misalignment, bellows or beam couplings are more appropriate.
Axial misalignment (end-float): Some axial play (shaft end movement) can be accommodated because the centre disc can move slightly in the axial direction between the two hub faces. However, Oldham couplings are not designed to absorb significant axial motion. If substantial axial displacement is anticipated, a coupling with an axial compliance element should be used.
The centre disc is the only moving interface in the coupling, and its material determines almost every practical performance characteristic. For general precision motion applications, acetal (POM) is the standard choice. Its natural lubricity allows the tenons to slide within the hub slots without grease, its dimensional stability keeps the fit consistent over temperature cycles, and its stiffness is high enough to maintain near-zero backlash throughout a long service life.
For higher temperatures or chemical exposure, PEEK discs are available. For very heavy loads, metal-on-metal variants with grease lubrication provide much higher torque capacity at the cost of dry-running convenience and the electrical isolation property that polymer discs provide.
Because the disc is a wear part — and in a well-designed Oldham coupling it is intended to be — most manufacturers offer replacement discs separately. When the disc eventually shows signs of wear, it can be swapped out in a few minutes without disturbing the shaft alignment or removing the hubs from the shafts.
Because the centre disc is in continuous sliding motion relative to the hubs during operation, friction and heat generation are always present. The severity of both increases with higher rotational speed and greater lateral offset. This creates a practical trade-off: you can run at high speed with minimal offset, or at lower speed with larger offset, but combining high speed with large offset generates excessive heat in the disc that will accelerate wear and ultimately compromise backlash performance.
Most polymer-disc Oldham couplings intended for precision applications carry speed ratings in the range of 3,000 to 6,000 RPM. Metal-disc industrial versions can operate at lower speeds with much higher torque. Always consult the manufacturer’s combined speed-and-offset derating curves when operating near either limit.
The mechanism described above makes the Oldham coupling well suited for any application where:
Common deployment environments include servo and stepper motor drives for CNC axes and linear stages, encoder and resolver feedback connections, medical laboratory instruments, packaging and converting machinery, and semiconductor wafer handling systems.
The Oldham coupling works by converting lateral shaft offset into a controlled, reciprocating sliding motion at the centre disc. This motion is fully absorbed within the coupling itself, so the shafts and their bearings see no radial force from the misalignment. Torque is transmitted through a positive form-fit interface that maintains zero backlash throughout the full rotation cycle. The result is a coupling that handles parallel offset better than any comparable design while simultaneously delivering the constant-velocity, backlash-free torque transmission that precision motion systems demand.
Browse our Oldham coupling product range to find the right size and hub configuration for your application, or speak to our engineering team for personalised selection guidance.
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