When you request a CNC machined part, one of the most important decisions you make is the tolerance grade. Too loose, and the part won’t fit. Too tight, and the cost skyrockets.
## Standard vs Precision vs Ultra-Tight
**Standard tolerance (±0.05 mm / ±0.002″)** — This is the default for most CNC milling and turning shops. Suitable for brackets, housings, and non-critical structural parts. Cost is lowest.
**Precision tolerance (±0.01 mm / ±0.0004″)** — Requires 3-axis or 5-axis CNC with in-process probing. Typical for medical devices, semiconductor equipment, and hydraulic components. Cost increases 30-50%.
**Ultra-tight tolerance (±0.005 mm / ±0.0002″)** — Requires climate-controlled inspection, CMM verification, and specialized tooling. Used for precision gauge blocks, optical mounts, and aerospace components. Cost can double.
## How to Choose the Right Tolerance
Ask yourself three questions:
1. Is this a mating surface or a free surface?
2. Does it affect assembly function or just appearance?
3. What is the production volume?
Most over-specification happens when designers apply ±0.01 mm tolerance to surfaces that don’t need it. This adds cost without functional benefit.
At Legend Precision, our engineering team reviews drawings before quoting and suggests tolerance optimizations that reduce cost while keeping critical dimensions tight. Contact us for a free DFM review.