Customers occasionally ask whether StepperOnline offers a ready-made adapter flange for mounting a harmonic (strain-wave) gearbox to a motor. This article explains why a universal adapter flange is not offered and why a custom-designed flange is typically required.
Why Harmonic Gearboxes and Motors Cannot Always Be Mounted Directly
The mounting interface between a harmonic gearbox and a motor depends on many variables—motor brand, frame size, shaft diameter, pilot (spigot) diameter, bolt-circle diameter (PCD), and the specific gearbox series and size. Because these dimensions differ from one combination to another, a single off-the-shelf flange cannot cover every pairing.
Core Reasons a Custom Flange Is Usually Necessary
1. Industry Standards Are Not Unified (Mounting Dimensions Vary Widely)
- Motor dimensions differ. Servo motors and stepper motors from different brands have different pilot diameters, shaft diameters, locating-pin holes, and bolt-circle diameters (PCD).
- Harmonic gearbox models differ. Harmonic gearboxes come in several form factors—Component type, Mini (integrated) type, hollow-shaft type, and others—each with its own input-side mounting dimensions. StepperOnline's harmonic gearbox lineup includes the HHD, HHT, and HSS series, and each series is further divided into multiple sub-sizes, resulting in a large number of possible mounting dimensions.
2. Tight Space Constraints in the Equipment
- Limited axial space. A standard, universal adapter flange is typically made thicker to accommodate a wide range of motors. In lightweight robotic arms or compact joint modules, such a thick flange simply cannot fit.
- Integrated structural requirements. In many designs the flange is not merely a connector; it also serves as a motor mount, support bracket, cable exit, or even a pneumatic passage. Highly integrated, non-standard structures such as robotic arms require a flange tailored to the overall machine layout.
3. Special Thermal and Sealing Requirements
- Heat dissipation. Under heavy loads a harmonic gearbox generates significant heat. A custom flange can be machined from a high-conductivity aluminum alloy (e.g., AL7075) and incorporate cooling fins to improve thermal performance.
- Sealing and ingress protection. In food-processing, pharmaceutical, or underwater-robot applications, the mounting flange may need dedicated O-ring grooves to achieve IP65 or IP67 protection. Standard flanges generally do not include these specialized waterproof and dustproof features.
Summary
Because of the wide variation in motor and gearbox mounting dimensions, tight space constraints, and application-specific thermal or sealing requirements, a single standard adapter flange cannot adequately address all real-world conditions. Designing a custom flange tailored to your specific motor, gearbox, and mechanical layout is the recommended approach.