CNC Machining Tolerance Standards Guide — ISO Metric Inch

Tolerance standards define acceptable dimensional variation in machined parts. Understanding the right tolerance level for each feature reduces cost without compromising function.

Standard Tolerance Tables (ISO 2768)

Dimension RangeFine (f)Medium (m)Coarse (c)
0.5-6 mm±0.05±0.10±0.20
6-30 mm±0.10±0.20±0.50
30-120 mm±0.15±0.30±0.80
120-400 mm±0.20±0.50±1.20
400-1000 mm±0.30±0.80±2.00

CNC Machining Capabilities

GD&T Basics

Geometric Dimensioning & Tolerancing (GD&T) defines the allowable variation in part geometry, not just size. Key symbols include: flatness (─), parallelism (//), perpendicularity (⊥), concentricity, position.

Cost Impact

Tighter tolerances increase cost exponentially: ±0.1 mm is baseline; ±0.05 mm adds 15-30%; ±0.02 mm adds 50-100%; ±0.005 mm adds 200-400% depending on feature complexity. Apply tight tolerances only on functional mating surfaces.

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