Design for Manufacturability, Not Just Precision.
A comprehensive guide to engineering tolerances and standards. Optimize your designs for cost, speed, and quality by understanding the practical limits of modern manufacturing.
CNC Tolerance Guide
Subtractive manufacturing offers the highest precision but cost scales exponentially with tighter tolerances. Focus precision on mating features and bearing seats while allowing standard tolerances for aesthetic surfaces.
CNC Practical Tolerance Ranges
| Feature Type | General/Standard | Precision | Critical/Tight | Cost Impact |
|---|---|---|---|---|
| Linear Dimensions | ±0.127 mm | ±0.050 mm | ±0.012 mm | low |
| Hole Diameters | ±0.050 mm | ±0.025 mm | ±0.005 mm | medium |
| Flatness/Straightness | 0.100 mm | 0.050 mm | 0.010 mm | high |
| Surface Roughness (Ra) | 3.2 μm | 1.6 μm | 0.4 μm | medium |
Pro Tip:
Never use the same tolerance for a flat laser-cut blank as a welded assembly. Thermal distortion in welding requires looser tolerances.
Injection Tolerance Guide
Molding tolerances are heavily influenced by material shrinkage, part geometry, and cooling rates. High-shrinkage materials like PP or PE are harder to control than low-shrinkage resins like ABS or PC.
Molding Tolerance Guidelines
| Feature Type | General/Standard | Precision | Critical/Tight | Cost Impact |
|---|---|---|---|---|
| Linear (Small Parts) | ±0.100 mm | ±0.050 mm | ±0.025 mm | medium |
| Wall Thickness | ±0.127 mm | ±0.075 mm | ±0.050 mm | high |
| Draft Angles | 1.0° – 2.0° | 0.5° | 0.25° | low |
Sheet Metal
Sheet metal fabrication involves bending, which introduces “springback.” Tolerances must account for the material thickness variations and the mechanical limits of press brakes.
Sheet Metal Fabrication Limits
| Feature Type | General/Standard | Precision | Critical/Tight | Cost Impact |
|---|---|---|---|---|
| Bending (Angle) | ±1.0° | ±0.5° | ±0.2° | medium |
| Hole to Edge | ±0.127 mm | ±0.075 mm | ±0.050 mm | low |
| Flat Pattern | ±0.250 mm | ±0.127 mm | ±0.075 mm | medium |
ISO / ASME / JIS References
ISO 2768
Standard for European and international projects where general title block notes are preferred.
Older national standards like DIN 7168.
ASME Y14.5
Standard for European and international projects where general title block notes are preferred.
Older national standards like DIN 7168.
JIS B 0405
Standard for European and international projects where general title block notes are preferred.
Older national standards like DIN 7168.
Measurement Methods
| Inspection Tool | Bore Diameter | Surface Flatness | Shaft Runout | Hole Position | Thread Pitch | Surface Finish |
|---|---|---|---|---|---|---|
| Caliper | Poor | N/A | Fair | N/A | ||
| Micrometer | N/A | N/A | N/A | N/A | ||
| CMM | Excellent | Excellent | Excellent | N/A | ||
| Dial Indicator | Good | Excellent | N/A | N/A | ||
| Profilometer | N/A | N/A | N/A | Excellent |