Motor shafts, which play a vital role in diverse fields such as industrial equipment, medical equipment, and automotive parts, are critical components that accurately transmit the rotational motion of a motor. To maximize motor performance, appropriate shape design tailored to the application, careful material selection, and high-precision machining techniques are essential.
In this article, we provide a detailed explanation of information that engineers can utilize in their daily work, covering everything from the basic roles and structure of motor shafts to representative types such as straight and stepped shapes, material properties of S45C and SCM, and major manufacturing processes such as turning and grinding.
| Supervised by: C.I. TAKIRON Corporation Electronic Devices Sales Group This article has been supervised based on the advanced technical expertise and insights we have cultivated since our founding in 1919 as a leading company in plastic processing. Our department continuously analyzes market trends and the latest technologies in ultra-compact, high-precision micro motors, focusing on providing high-value-added information to designers and developers. As a team of experts with in-depth knowledge of product characteristics, we support our customers’ problem-solving and technological innovation by delivering accurate and practical content. 。 |
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What Is a Motor Shaft?
A motor shaft is a rotating shaft that transmits the rotational motion of an electric motor to external equipment. Its applications range widely, from industrial pumps to automotive traction motors, and it is a component designed individually to meet specific requirements for diameter and shape . As a critical component requiring durability to withstand high-speed rotation and precision in coaxiality, its quality significantly impacts the overall performance and reliability of the motor.
Topics Covered in This Section
- Basic Structure and Role of Motor Shafts
- Main Applications of Motor Shafts
- Performance Requirements for Motor Shafts
The following explains the basic structure and role of motor shafts, their main applications, and the performance required of them.
Basic Structure and Role of Motor Shafts
A motor shaft consists of three main components: the rotating shaft body, the bearing section, and the power transmission section. The rotating shaft body is a cylindrical component that runs through the center of the motor and serves as the foundation for rotational motion. The bearing section, which comes into contact with the bearings, requires high roundness and a smooth surface finish. If the contact surface has irregularities or warping, vibration and wear during rotation increase, which shortens the motor’s lifespan.
The power transmission section is machined with keyways, splines, threads, and other features to ensure a secure connection with other components. Keyways are designed to secure gears and pulleys, preventing slippage during rotation. Splines feature multiple teeth machined into the outer circumference of the shaft, enabling the transmission of higher torque.
Main Applications of Motor Shafts
In the medical equipment sector, they have been adopted as the power source for endoscopic cameras and surgical pumps. Particularly in medical and optical equipment where high control precision is required, precise operation is made possible through the use of Coreless motors. In the automotive sector as well, they play a crucial role, such as supporting driving performance as the main motor in electric vehicles. While the performance required varies by application, high reliability and precision are common requirements.
Performance Requirements for Motor Shafts
Motor shafts require coaxiality accuracy to suppress vibration during high-speed rotation, as well as durability and wear resistance to withstand long-term use, and the ability to reliably transmit torque. Low coaxiality accuracy—which indicates misalignment of the shaft’s rotational center—can cause abnormal noise and vibration. The surface roughness of the bearing contact area is strictly controlled to prevent wear; if the surface is rough, friction with the bearings increases, leading to heat generation and accelerated wear.
Since fatigue strength is a key factor in durability, performance is ensured through careful material selection and heat treatment. Depending on the application, corrosion resistance and non-magnetic properties may also be required; for example, stainless steel is essential for medical equipment, and non-magnetic materials are indispensable for components used in MRI environments. Particularly in medical and precision equipment, combining these shafts with Coreless motors—which lack an iron core—enables smooth, cogging-free rotation and high-precision control.
Types and Materials of Motor Shafts
The optimal shape and material for a motor shaft are selected based on the type of components to be mounted, the required torque, and precision requirements. The basic shapes are straight and stepped, and for securing pulleys or gears, there are keyway and flat shapes.
Regarding materials, S45C is the most widely used; alloy steels such as SCM435 are chosen when higher strength is required; and stainless steels such as SUS303 or SUS304 are selected for environments where corrosion resistance is essential.
Contents of this section
- Straight and stepped shapes
- Keyway and Flat Shapes
- Properties of S45C, SCM, and Stainless Steel
Below, we provide a detailed explanation of the characteristics of typical shapes and the properties of each material.
Straight and stepped shapes
The straight shape is the simplest structure, featuring a uniform diameter along its entire length. Its major advantages are ease of machining and low cost. Since it can be manufactured primarily by lathe machining, lead times can be shortened, making it suitable for compact motors and general-purpose motors. Although design flexibility is limited, it is the optimal choice for applications where the bearing and power transmission sections can be constructed with the same diameter.
On the other hand, the stepped shape, which features multiple steps, allows the diameters of the bearing section and the power transmission section to be set individually. Since the steps function as positioning stops for components, they improve positional accuracy and work efficiency during assembly. For example, by designing the bearing section to be thinner and the gear mounting section to be thicker, it is possible to achieve both smaller bearings and higher torque transmission capacity simultaneously.This stepped design is also highly valuable in medical equipment and precision equipment where multiple functional components are arranged on a single shaft.
Keyway and flat profiles
A keyway design involves machining a narrow groove into the outer circumference of a shaft and inserting a key to securely fasten gears or pulleys. The interlocking of the key and the groove prevents slippage during rotation and allows for the efficient transmission of high torque. This method is widely used in high-load applications such as industrial pumps and machine tools. Keyway dimensions are standardized by JIS and other standards, enabling designs with excellent compatibility.
The flat design involves machining a portion of the shaft flat and securing the component with a set screw. This structure is simpler to machine than a keyway and is suitable for compact motors and low-torque applications. Since the set screw is secured by its tip engaging with the flat surface, installation and removal are easy. Both methods are effective for preventing slippage, but the appropriate choice depends on the required torque and cost considerations.
Properties of S45C, SCM, and Stainless Steel
S45C is a medium-carbon steel with a carbon content of approximately 0.45%, offering excellent strength and machinability. It has a tensile strength of approximately 570–750 MPa and a hardness of approximately HB 160–220, and is widely used in general industrial equipment and power tools. It is easy to machine, and its surface hardness can be increased through heat treatment, providing a good balance between cost and performance.
SCM steel is an alloy steel containing added chromium and molybdenum, making it suitable for applications requiring higher strength. SCM435 boasts high mechanical properties, with a tensile strength of 930 MPa or higher and a hardness of approximately HB 269–331, and is used in demanding conditions such as automotive parts.
In medical equipment and food processing machinery, where corrosion resistance is a priority, stainless steel is commonly used. SUS303 offers excellent machinability and is easy to process, while SUS304 is a general-purpose material with high corrosion resistance; the choice depends on the specific environment. In environments where non-magnetic properties are essential, such as MRI settings, special steels like SUS316 may be selected.
Motor Shaft Machining Methods
The manufacture of motor shafts involves a combination of multiple processes, including turning, grinding, gear cutting, rolling, and heat treatment.
Topics Covered in This Section
- Material Cutting and Centering
- Turning and Grinding
- Gear Cutting, Roll Forming, and Heat Treatment
Below, we provide a detailed explanation of the purpose and importance of each machining process.
Material Cutting and Centering
After cutting the material to the required length based on the drawings, both end faces are machined on a centering machine to create center holes that serve as reference points for the rotational axis. Since these center holes act as reference points for securing the shaft during subsequent turning and grinding processes, positional accuracy is of the utmost importance.
Accurately achieving the required flatness and concentricity in this process is a critical factor that determines the machining accuracy of subsequent operations. If the end faces are tilted or the hole is misaligned, the shaft will rotate eccentrically during turning, making it difficult to ensure roundness. For material cutting, band saws and circular saws are generally used to maintain perpendicularity.
It is also essential to strictly control cutting speed to minimize burrs and warping during cutting. After centering is complete, it is crucial to rigorously verify that the hole depth and angle are within specification.
Lathe Machining and Grinding
Turning is a process in which a rotating workpiece is machined with cutting tools to form basic shapes such as outer diameters and steps. CNC lathes achieve high repeatability and can accurately machine complex stepped and tapered shapes.
In turning, machining accuracy and surface finish are improved by optimizing cutting speed, feed rate, and depth of cut.Grinding is a high-precision finishing process that finely removes material from the surface using a grinding wheel to achieve dimensional accuracy and surface roughness at the micron level. Depending on the required specifications for parts such as bearings, cylindrical grinders are used to create surfaces that meet these requirements. Grinding makes it possible to achieve levels of roundness and concentricity that are difficult to attain with turning alone.
During machining, coolant is used to suppress heat generation and prevent dimensional errors caused by thermal expansion. Finally, each dimension is measured using a coordinate measuring machine (CMM) or similar equipment to verify compliance with quality standards.
Gear Cutting, Roll Forming, and Heat Treatment
We perform gear cutting on a hobbing machine and rolling on a rolling machine to form spline and gear shapes. Gear cutting is a method that uses cutting tools to cut teeth into the outer circumference of a shaft, and it is characterized by its flexibility in handling complex tooth profiles. When using a hobbing machine, a cylindrical tool is rotated while being pressed against the shaft to continuously cut out the teeth.
In contrast, rolling—which involves the plastic deformation of the material—offers superior durability because it hardens the surface. By applying pressure with a rolling die, the material’s fiber flow remains intact, leading to improved fatigue strength. Since processing time is shorter compared to cutting, this method is well-suited for mass production. Furthermore, heat treatments such as high-frequency hardening or carburizing are performed to increase surface hardness.
The former method involves rapidly heating and cooling only the surface to harden it, achieving high hardness while maintaining the toughness of the core. The latter method involves diffusing carbon into the material, which is expected to improve wear resistance through a deeper hardened layer. After heat treatment is complete, the part is straightened to correct any distortion, then re-ground to achieve the final dimensions.
Summary
The motor shaft is a critical component that accurately transmits the motor’s rotational motion, requiring shape design, material selection, and high-precision machining techniques tailored to the specific application. This article explains the basic structure and role of motor shafts, representative types such as straight and stepped shapes, the characteristics of materials like S45C and SCM, and major manufacturing processes such as turning and grinding.
For industrial and medical equipment requiring precise control, Coreless motors are ideal because they achieve smooth, cogging-free rotation—a factor that directly impacts performance by minimizing rotational irregularities and vibration. Due to their core-less design, Coreless motors exhibit minimal rotational irregularities and vibration, enabling high-precision positioning and speed control. C.I. Takiron Corporation offers high-performance Coreless motors and can customize them to meet your specific application needs. Please feel free to contact us.
Product Information & Inquiries
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