What type of allowance exists when a roller bearing is pressed onto a shaft?

When a roller bearing is pressed onto a shaft, a negative allowance is typically present. This condition occurs because the inner diameter of the bearing is designed to be slightly smaller than the outer diameter of the shaft. This slight difference in measurement is intended to create an interference fit, which ensures a secure and stable connection between the bearing and the shaft.

The negative allowance is crucial for performance, as it allows the bearing to withstand operational stresses without slipping or loosening during use. This fit generates a strong connection that is essential for the efficient operation of machinery, especially in high-load applications. By designing this interference, engineers ensure that the bearing will stay in place and maintain proper alignment with the shaft, which is vital for optimal functionality and longevity of the mechanical components.