Failures can occur in brushless alternators due to interferences between the moving and stationary parts, called “rub.” Improper design of component target dimensions and tolerances can result in interferences. A method was developed to evaluate the component tolerances that can create interference in a brushless alternator. Mathematic models were created to relate target dimensions to the interferences. Monte Carlo simulation was utilized to statistically evaluate the effects of tolerances on failure rate. This method allows a designer to avoid potential rub failures while still in the design phase. It can also be used to analyze rotary machines of similar designs.