Back to notes

January 18, 2026 - 1 min read

Tolerance Stack-Up Checklist for Early Design Reviews

A quick review structure I use to catch fit and assembly risk before release.

Last updated: 2026-02-24

Why this checklist exists

Most tolerance failures are not caused by one bad dimension. They come from small assumptions that stack together across interfaces.

Review sequence

  1. Identify all functional interfaces tied to fit, preload, or alignment.
  2. Define the critical direction for each stack (axial, radial, angular).
  3. Assign datum strategy and verify consistency across mating components.
  4. Compute worst-case and statistical bounds for each stack.
  5. Confirm manufacturing process capability supports selected limits.

Quick acceptance checks

Clearance Margin

>= 0.20 mm

At min tolerance condition

Assembly Force

< 80 N

For hand assembly station

Rework Risk

Low

No selective-fit required

Common misses

  • Datums that shift between CAD and drawing release.
  • Press-fit assumptions reused on printed parts.
  • Missing thermal-growth consideration for mixed materials.