Tolerance design for the fit between bore and shaft for precision assemblies with significant error-scaling problems

Abstract

An inspection procedure may be necessary when a process does not have the capability to produce parts that meet specifications. After inspection, the accepted parts then have a probability density function which is truncated. In a previous paper, the authors presented a method for the computation of tolerances for the fit between a bore and a shaft, based on the construction of a probabilistic model of the fit, using truncated probability density functions for the bore and shaft. In this paper, a method of design is presented for the computation of tolerances for the bore and shaft that are necessary to satisfy the tolerance of the fit and at the same time minimize the probability of rejection for the processes that produce the bore and shaft. Application is made to the situation where the variations in the dimensions of the parts may be large compared with their nominal dimension or the fit requirement of the assembly. Such a situation will be denoted as the error-scaling problem.

Keywords:

• Design of fit
• Fit condition
• Inspection
• Operating characteristic
• Precision assemblies
• Process capability index
• Quality assurance
• Quality control
• Tolerance
• Truncated probability density function

Acknowledgement

This research is supported in part by NSF Award # DMI-0355125 and 0355214.