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Engineering Guide

Understanding Oldham Coupling Design: Selection, Performance, and Application

The Three-Piece Architecture

The Oldham coupling takes its name from John Oldham, who patented the three-piece sliding-disc mechanism in 1821 to transmit rotary motion between parallel but offset shafts. The design has remained fundamentally unchanged because it solves an enduring mechanical problem elegantly: how to couple two misaligned shafts without generating bending moments that damage bearings.

The assembly consists of two outer hubs and a centre disc. Each hub carries a rectangular tongue machined perpendicular to its face. The centre disc carries two grooves oriented 90° to each other, one on each face. The tongue of hub A slides in one groove of the disc; the tongue of hub B slides in the opposing groove. This arrangement ensures that regardless of the lateral offset between the two shaft centrelines, the centre disc transmits full torque while sliding radially to absorb the misalignment — generating no axial reaction force on either shaft.

Material Selection for Centre Disc Performance

The centre disc is the consumable wear element in an Oldham coupling, and material selection has a direct impact on torque capacity, service life, operating speed, and system noise level.

PA66 Nylon is the most widely used disc material for standard servo motor and stepper motor applications. It offers a good balance of tensile strength, surface hardness, and self-lubricating properties. The sliding contact between the aluminium hub tongue and the nylon groove produces low friction and acceptable wear rates at typical servo speeds of 1,000 to 3,000 rpm.

POM (Polyoxymethylene / Delrin) provides higher dimensional stability than nylon, lower moisture absorption, and improved surface finish. These properties make POM the preferred disc material in semiconductor and optical equipment where dimensional consistency across temperature cycles is critical. POM discs also exhibit better chemical resistance against cutting fluids and cleanroom solvents.

Polyurethane (PU) discs are specified where torque peaks and vibration damping are priorities rather than maximum speed. PU material absorbs shock loads and reduces transmission of rotational vibration, making it effective in packaging lines with cyclic indexing loads. The trade-off is higher sliding friction compared to nylon, so PU discs are not recommended above 3,000 rpm without specific verification.

Hub Material and Surface Treatment

Hub bodies are machined from 6061 aluminium alloy as standard. The alloy offers an excellent strength-to-weight ratio, high machinability for tight bore tolerances, and natural corrosion resistance. Black anodising provides additional surface hardness and a professional finish that prevents galvanic wear at the tongue contact faces. For applications in wet, hygienic, or chemically aggressive environments, SS304 stainless steel hubs are available at a material premium.

Selecting Bore and Fixation Method

Both set screw and clamping hub designs are offered across the product range. Set screw fixation uses one or two radial grub screws that bear against the shaft surface or a flat machined on the shaft. This provides adequate holding torque for light and medium duty cycles and is the lower-cost option for high-volume machine builds. However, repeated assembly and disassembly of set screw hubs can damage shaft surfaces over time.

Clamp-style hubs use a split bore and a tangential bolt to generate uniform radial clamping force around the shaft circumference. This method causes no localised stress concentration and preserves shaft surface integrity through many assembly cycles. Clamp hubs are the preferred choice for servo motor output shafts where shaft surface condition must be maintained for warranty compliance.

Bore diameters are available in standard metric and inch sizes. Custom bores and keyways are machined to order when standard dimensions do not match a specific shaft specification.

Coupling Selection Procedure

Correct Oldham coupling selection involves four key parameters: required torque capacity, shaft bore diameters, maximum operating speed, and radial misalignment. Begin by calculating the peak torque, including application service factors for start-stop cycles, load reversals, and shock loads. Choose a coupling series whose rated torque exceeds this figure by at least 20% as a safety margin.

Verify that the bore size range of the selected series accommodates both shaft diameters — they do not need to be equal. Check the operating speed against the maximum rpm rating of the series and disc material combination. Finally, measure or estimate the expected shaft-to-shaft parallel offset in the assembled machine and verify it sits within the ±0.5 mm to ±1.5 mm range depending on coupling size.

If your application parameters are at the boundary of a series rating, contact our technical team at [email protected] with your drive data. We will assess the duty cycle and recommend the most appropriate configuration, including disc material and fixation method.

Installation and Alignment Best Practices

An Oldham coupling tolerates misalignment, but the installation should still aim to minimise offset to preserve disc life. Use a dial gauge or laser alignment tool to bring shaft centres as close as practical — residual misalignment below 0.3 mm produces negligible disc wear and is entirely acceptable. Excessive deliberate misalignment beyond rated values will reduce disc service life proportionally and may introduce rotational torque ripple in precision servo axes.

Tighten set screws to the manufacturer torque specification and verify that both hubs are positioned so that the disc can be removed axially without disturbing either shaft mounting. This preserves the quick-change maintenance advantage that the Oldham design provides.

For further guidance on installation and maintenance, our technical team is available through the contact page. technical documentation models in dimensional are provided with all orders to facilitate digital verification in your machine assembly environment.