Shaft parts are the core transmission components in automation machinery, automotive systems, and industrial equipment—their tolerance control directly determines the stability, wear resistance, and service life of the entire mechanical system. Even a tiny tolerance deviation (as small as ±0.001 mm) can lead to component jamming, increased noise, or even complete equipment failure.

In this article, we will share practical techniques and key steps to control tolerance in shaft parts machining, helping you avoid common pitfalls and improve product quality.

Key Tolerance Indicators for Shaft Parts Machining

• Dimension Tolerance: The allowable variation of the shaft’s outer diameter, length, and step size. For example, the outer diameter of a robot arm shaft may require a dimension tolerance of φ20±0.002 mm to fit with bearings.
• Coaxiality Tolerance: Ensures that the central axes of multiple cylindrical features (e.g., journals, steps) on the shaft are aligned. Typically required to be within 0.002–0.005 mm for rotating shafts in automation machinery.
• Circular Runout Tolerance: Controls the deviation of the shaft’s outer surface during rotation, which affects the smoothness of motion. For high-speed rotating shafts, runout tolerance is usually limited to ≤0.003 mm.
• Surface Roughness (Ra): A smooth surface reduces friction and wear. Shaft parts in contact with bearings or seals typically require Ra ≤0.8 μm, while precision mating surfaces need Ra ≤0.2 μm.

6 Core Techniques for Tolerance Control in Shaft Parts Machining

1. Optimize Blank Selection and Pre-Processing

2. Choose the Right Machining Equipment and Tools

3. Rational Machining Process Design: Rough Machining + Semi-Finish Machining + Finish Machining

• Rough Machining: Remove 70–80% of the excess material quickly, with a large cutting depth (2–3 mm) and moderate cutting speed. The goal is to improve efficiency while leaving a uniform machining allowance (0.5–1 mm) for subsequent processes.
• Semi-Finish Machining: Remove most of the remaining allowance (0.1–0.2 mm left), correct the shape deviation caused by rough machining, and improve the surface flatness and coaxiality.
• Finish Machining: Use small cutting depth (0.05–0.1 mm) and high cutting speed (1500–3000 rpm, depending on material) to achieve the required tolerance and surface finish. For ultra-high-precision shafts, we add a grinding process after turning to further reduce surface roughness and ensure dimension stability.

4. Strict Fixture Design and Clamping Methods

• For slender shafts (length-diameter ratio >10), we use a "two-center positioning + steady rest" clamping method to prevent bending deformation during machining.
• For stepped shafts with multiple diameters, we use a combination of a chuck and a center frame to ensure coaxiality between different steps.
• We control the clamping force strictly—too much force will cause elastic deformation of the shaft, while too little force will lead to workpiece displacement during cutting. Pressure sensors are used to monitor clamping force in real time for high-precision projects.

5. Control Thermal Deformation During Machining

• Cutting Fluid Cooling: Use high-pressure cutting fluid (pressure up to 20 MPa) to spray the cutting area continuously, reducing cutting temperature and take away the chips quickly.
• Intermittent Machining: For long shafts or high-hardness materials, we adopt intermittent machining (machining for 30 seconds, stopping for 10 seconds) to allow the workpiece to cool down and avoid thermal accumulation.
• Ambient Temperature Control: Our machining workshop maintains a constant temperature of 20±2 ℃, which minimizes thermal deformation of the machine tool and workpiece—critical for ultra-high-precision tolerance control.

6. Comprehensive Quality Inspection and Feedback Adjustment

• In-Process Inspection: Operators use dial indicators, micrometers, and depth gauges to check key dimensions and coaxiality after semi-finish machining, adjusting machining parameters in time if deviations are found.
• Final Inspection: Use Coordinate Measuring Machines (CMM) to perform 100% inspection of critical dimensions and geometric tolerances for high-precision shafts. The CMM can measure up to 0.0001 mm, ensuring all indicators meet design requirements.
• Data Feedback: We record all inspection data and analyze the causes of any deviations (e.g., tool wear, thermal deformation). This data is used to optimize machining parameters for subsequent batches, forming a closed-loop quality control system.

Bomei’s Advantage in Shaft Parts Tolerance Control

• Achieve tolerance accuracy of ±0.001 mm for high-precision shafts, meeting the strict requirements of the automation machinery industry.
• Provide customized machining solutions according to your specific tolerance requirements, material characteristics, and production volume.
• Ensure consistent tolerance accuracy across batches, avoiding quality fluctuations caused by manual operations.
• Deliver on time even for tight-turnaround projects, thanks to optimized processes and efficient production scheduling.