How to distinguish tolerances of inner holes of sprockets

The main difference in the tolerance of the inner bore of the sprocket is reflected in the "tolerance level" and "size range". The lower the tolerance level, the higher the accuracy, and the stricter the control of the aperture size, but it usually increases the cost; conversely, the higher the tolerance level, the larger the allowable dimensional change range, and the lower the cost. In practical applications, it is necessary to select appropriate tolerance levels and dimension ranges based on the operating accuracy requirements of the sprocket, the mating requirements of the shaft and the economy.

 1. Tolerance level (Tolerance band) • Definition: Tolerance level is the sum of allowable dimensional changes in the aperture or shaft diameter, represented by a combination of letters and numbers. • Value: The smaller the number, the smaller the tolerance and the higher the accuracy (such as level 6, level 7, etc.). • Significance: ◦ Accuracy requirements: High-precision sprockets usually use low tolerance levels (e.g., for precision instruments or high-speed equipment) to reduce vibration and noise and improve transmission efficiency. ◦ Cost consideration: Low tolerance levels mean higher requirements for processing accuracy and production costs will also increase accordingly. 

2. Size range (upper and lower limit of aperture) • Definition: Inner bore tolerance also includes the upper and lower limit of specific apertures under tolerance levels. • Calculation: It is calculated based on the base size (nominal size) and the selected tolerance level. • For example: A hole with a nominal diameter of 50mm, the actual dimensions of the inner hole must be within a specific range (for example, between 50mm ± 0.025mm), which is the upper and lower limits of the dimensions. 

3. How to distinguish between choices • Cooperation requirements: Determine the fit between the inner hole of the sprocket and the shaft, whether it is a tight fit, a transition fit or a clearance fit. Different fitting methods have different tolerance requirements for holes. • Accuracy requirements: To analyze the use scenarios of the sprocket, whether extremely high transmission accuracy is required to select the appropriate tolerance level. • Economic analysis: Select a relatively low-cost tolerance level and dimension range while meeting the requirements of accuracy and coordination. Summary: The key to choosing tolerances for the inner hole of the sprocket is balance accuracy requirements, coordination method and economy, and ensure the good operation of the sprocket by selecting the appropriate tolerance level and determining the upper and lower limits of the dimensions.