Micro Gearbox selection guide – How to choose gearbox shaft

In micro gearbox applications, the gearbox shaft plays a pivotal role by transmitting the motor’s mechanical energy to the intended application, serving as the critical…

In micro gearbox applications, the gearbox shaft plays a pivotal role by transmitting the motor’s mechanical energy to the intended application, serving as the critical link between the gear motor and your machinery.

But how do you select the ideal output shaft?

The answer lies in balancing several key factors: material strength, connection design, torque resistance, and environmental conditions. Each factor is crucial in ensuring that the shaft not only performs efficiently under load but also meets the specific demands of your operational environment.

In this article, we draw on SGMADA’s 20 years of expertise in output shaft design to guide you toward the optimal solution for your micro gearbox application.

4 Factors we consider about Gearbox shaft

When selecting the right output shaft for your micro gearbox, focus on these four key factors:

1.Material Strength

The material selection for the gearbox output shaft primarily hinges on two factors:

Material Strength: The material must have sufficient strength to endure operational loads.
Production Cost: The cost-effectiveness of manufacturing the output shaft is a key consideration.

Material	Strength	Cost	Processing
Stainless Steel (304/316)	+	–	Conventional machining & welding
Carbon Steel	+	+	Standard machining
Titanium Alloy	++	–	Specialized machining techniques
Engineering Plastics (POM)	–	+	Injection molding & plastic processing

Important Notice:
In typical gearbox applications, plastic materials are generally not used for output shafts due to their insufficient strength. For most gear transmission scenarios, metal alloys like stainless steel, carbon steel, or titanium are preferred to ensure robust performance and safety.

2.Connection Design

The shape of the output shaft should be selected according to the specific application of the gear motor. The connection method of the gear output shaft with different mechanical structures determines its shape design.

Shaft Type	Features	Diagram Illustration
Round Shaft	Simple, robust design for moderate torque	O
Keyed Shaft	Includes a key slot for secure connection	O▭
Splined Shaft	Multiple grooves for even torque distribution	O[=]
Threaded Shaft	External threads for fastener attachment	O~~~~
Hollow Shaft	Lightweight with a hollow center	O (hollow)
Integral Gear Shaft	Gear teeth integrated along the shaft	O⚙

3.Torque Resistance

Torque resistance is key to ensuring the output shaft’s durability and reliability, allowing it to safely transmit the required torque without failure, deformation, or excessive wear. Several factors should be considered when confirming the shaft operates within the required torque range:

Torque Load Calculation:
Calculate the expected torque based on motor power and gear ratio to determine the minimum torque the shaft must handle to avoid failure.
Material Selection:
Materials like alloy steel, stainless steel, or titanium, with high tensile and yield strength, are chosen for better stress resistance and fatigue endurance.
Shaft Diameter:
A larger shaft diameter helps withstand higher torque. Proper sizing based on material strength and applied torque ensures the shaft resists bending or twisting.
Safety Factor:
Design the shaft to handle torque spikes beyond the expected maximum, ensuring it can withstand unexpected load fluctuations.
Fatigue Resistance:
Repeated torque cycles can lead to material fatigue. Using fatigue-resistant materials and optimizing shaft geometry (e.

4.Environmental Conditions

Environmental conditions are also a factor in gear output shaft selection, as they directly affect material performance and durability. Output shafts must be designed to withstand specific environmental challenges, such as corrosion, high temperatures, or low temperatures.

Environmental Condition	Description	Materials/Coatings
Corrosion Resistance	For humid or chemically aggressive environments.	Stainless steel, nickel/zinc plating
High Temperature	High temperatures can weaken materials.	Titanium alloys, heat-treated steel, ceramics
Low Temperature	Low temperatures can make materials brittle.	Stainless steel, specialty alloys
Environmental Coatings	Surface treatments to improve resistance.	DLC, PTFE coatings

How we machine the gearbox shaft?

At SGMADA, we use efficient and precise methods to machine the gearbox shaft, ensuring high quality and reliability. Our process includes:

1. Machining Process

At SGMADA, we use the following methods to machine the gearbox shaft:

CNC Machining:
We use CNC machines to precisely shape and cut the gearbox shaft to meet exact specifications, ensuring high accuracy and consistency.
Spline Hobbing:
For shafts that require splines, we use spline hobbing to create keyways or splines, allowing for secure connections with other components.

2. Surface Treatment

After machining, we apply the following surface treatments to enhance the shaft’s durability:

Heat Treatment:
This process improves the shaft’s hardness and strength, making it more resistant to wear and fatigue.
Electroplating:
We apply electroplating (nickel or zinc coatings) to improve corrosion resistance, ensuring the shaft performs well in harsh environments.

How to incorporate the gearbox shaft into applications?

Step1.Calculate the torque load on the gearbox shaft

Based on the torque requirements of the system, determine the maximum torque that the shaft needs to withstand. This value will directly affect the selection of appropriate materials and shaft diameter. The shape of the shaft (such as round shaft, keyway, spline, etc.) must also match the load requirements.

The minimum shaft diameter based on the given torque formula：

$$T = \frac{\pi d^3 \tau}{16}$$

can be calculated using the following expression:

$$d = \frac{2 \cdot 2^{\frac{1}{3}} \cdot \left( \frac{T}{\tau} \right)^{\frac{1}{3}}}{\pi^{\frac{1}{3}}}$$

Where:

T is the torque applied to the shaft
τ is the shear stress of the material.

Step2.Consider the type of load: steady load vs. shock load

Constant Load:
For continuous loads, choose a standard carbon steel shaft with a keyway design, which effectively transmits uniform torque.

Shock Load:
For high-impact loads, select an alloy steel shaft with a spline design and increase the safety factor to improve shock resistance and durability.

Step3.Considering the Impact of the Environment on the Output Shaft

As a last step, we should consider the material and process of the output shaft from the working environment of the output shaft.

Environment	Material/Design	Purpose
High Temperature	Titanium alloys, heat-resistant steel	Maintain strength at high temps
Low Temperature	Stainless steel, low-temperature alloys	Prevent brittleness at low temps
Corrosive Environment	Stainless steel, corrosion-resistant coatings (e.g., nickel, zinc plating)	Resist corrosion in harsh conditions

Gearbox shaft Practical Tools Recommendation

Shaft Strength Calculation Software (e.g., MITCalc Shaft Design):
MITCalc Shaft Design is a reliable tool for calculating the strength, dimensions, and stress of shafts. It helps in designing shafts that meet required load and safety standards, ensuring optimal performance in gear systems.

3D Model Libraries:
For ease of design and component integration, you can use 3D model libraries like TraceParts or GrabCAD. These platforms offer extensive collections of standard shaft and gear models, allowing you to quickly download and implement pre-made components into your projects.