Educational Resource

This is an educational case study based on common industry practices and methodologies documented in peer-reviewed literature. While scenarios are realistic, they represent composite examples for learning purposes.

This case study is an educational composite example based on tolerance analysis methodologies documented in the NIST/SEMATECH e-Handbook of Statistical Methods and peer-reviewed literature on dimensional variation management in precision mechanical assemblies.

NIST/SEMATECH e-Handbook of Statistical Methods — Uncertainty Analysis & Tolerance Intervals

NIST/SEMATECH

NIST Engineering Statistics Handbook • 2012

Tolerance Stack-Up Analysis in Precision Assembly

An educational case study demonstrating how 1-D tolerance stack-up analysis — using both worst-case and Monte Carlo methods — is applied to a multi-component mechanical assembly for clearance verification and interference prevention.

Case Study Overview

The Challenge

• • 5-component precision shaft-housing assembly
• • Field returns due to intermittent interference (binding)
• • Current tolerance scheme based on engineering judgment only
• • Need to quantify actual assembly risk with data
• • Cost pressure — avoid unnecessary tolerance tightening

Educational Outcomes

• • Signed Dimensional Chain
• • Worst-Case Analysis
• • Monte Carlo Simulation
• • Contribution Ranking
• • Tolerance Reallocation

Problem Definition & Current State

Understanding the assembly failure and dimensional contributors

Assembly Description

A precision rotary actuator requires a functional clearance gap between the shaft assembly and the housing bore. The gap is formed by 5 contributors arranged in a linear dimensional chain:

1. Housing Bore (ID)

Nominal: 50.000 mm, Tolerance: ±0.025 mm

2. Shaft OD

Nominal: 49.500 mm, Tolerance: ±0.015 mm

3. Bearing Width

Nominal: 0.200 mm, Tolerance: +0.010/−0.000 mm

4. Spacer Thickness

Nominal: 0.050 mm, Tolerance: ±0.020 mm

5. Retaining Ring Groove Depth

Nominal: 0.030 mm, Tolerance: ±0.010 mm

Current Performance

Business Impact

Warranty Cost

$42K/month in field replacements

Customer Satisfaction

NPS dropped 12 points in Q3

Regulatory Risk

Potential CAPA required if trend continues