38 n MECHANICAL POWER TRANSMISSION June 2026 www.drivesncontrols.com What it takes to make a custom gearbox A fully customised gearbox is typically specified when the compromises associated with offthe-shelf products become unacceptable. Constraints around space, weight or cost often mean standard gearboxes fail to optimise overall system performance, particularly in compact or high-demand applications. According to PW Consulting’s Worldwide Industrial Single-stage Gearbox Market Research Report 2026, “over 60% of end-users expressed a preference for customisable options that meet their unique operational requirements”. Custom boxes are also needed when applications demand materials or features not available in off-the-shelf products. Harsh or specialised environments may need enhanced ingress protection, nonoutgassing materials or application-specific lubricants. In many cases, customisation also allows multiple components to be consolidated into a single gearbox to simplify procurement, assembly and system design. These requirements are crucial in sectors such as medical technology, where gearboxes must use non-corrosive materials, have smooth, cleanable surfaces, and low weights – particularly in handheld devices. Customers rarely have a fully defined specification. Instead, bespoke design begins by developing a system-level understanding of the application, using physical modelling and theoretical calculations to define key parameters such as loads, speeds, duty cycles and service life. If there is an existing gearbox, it may be possible to reverse engineer and analyse its real-world performance, often identifying quality or reliability issues caused by off-theshelf gearboxes being used beyond their datasheet limits. By instrumenting systems with sensors and capturing operating data, it is possible to develop accurate specifications within the constraints of the available space and system behaviour, enabling a robust, fitfor-purpose gearbox design. Balancing compromise Custom gearbox development is defined by a few recurring trade-offs – most commonly performance versus cost, and performance versus size or weight. Users often seek high torque densities, compact packaging and long service lives, while also expecting a custom gearbox to remain at a competitive price. Managing these competing demands is a key part of the design process. In his Servo Gearbox Secrets 2025 book, Mike Gulliford emphasises the growing importance of precision in modern gearbox technology. “The demand for higher accuracy, efficiency, and reliability in components across industries is increasing – and gearbox selection is often underestimated,” he points out. From a performance perspective, gearboxes must meet clearly defined requirements for load, speed and duty cycle. But achieving these targets has cost implications, especially when using bespoke components or high-end materials. To manage this, you may want to reduce component counts, limit the use of fully bespoke parts, or introduce proven proprietary components where appropriate. In some cases, functions may be simplified to achieve a better balance between cost and performance. This is where motor selection becomes a clear contributor to these trade-offs. Highperformance motors can deliver the required power within tight spatial constraints, but their cost must be considered alongside the gearbox design. The final answer is often a system-level compromise rather than a gearbox-only decision. Constraints around size and weight create further complexity. Where the available envelope is fixed, maintaining performance may require adjustments elsewhere, such as reducing safety factors or optimising material selection. It is possible to balance this through detailed verification calculations, ensuring that critical components such as gear teeth and bearings remain robust even if space is limited. Safety factors can be applied to account for real-world uncertainties that cannot be fully simulated, such as load variations, thermal effects and manufacturing tolerances. Gear teeth and bearings are typically designed with margins of 1.5 to 2 times the expected operating load, ensuring that stresses remain well below material yield limits. These margins are reviewed and refined during prototyping and testing, where designs can be reinforced if required. Material choices also plays a key role in this balance. While commercial-grade steels are cost-effective and well understood, medical and aerospace applications often need lighter, corrosion-resistant or higher strength-to-weight materials, such as stainless steels or titanium alloys. These materials enable compact, lightweight designs but are more challenging to verify and manufacture, meaning that prototyping is used to confirm performance. Simulation, prototyping and testing all play important roles in validating custom Whether it’s the whisper-quiet precision needed for medical devices or the durability required in aerospace applications, finding ideal drive systems can be a challenge. The answer often lies not in compromise, but in customised gearboxes. Chris Handcock, design lead at the micromotor supplier and custom gearbox manufacturer EMS, looks at what it takes to create a custom gearbox. A multi-stage gearbox and worm drive customised for a specific application
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