Die Casting Tolerance Guide: NADCA Standards and Practical Limits
Die casting tolerances per NADCA for aluminum, zinc and magnesium: linear, parting-line and moving-die limits, plus draft angles and wall-thickness practical guidance for drawings.
Die Casting Tolerance Guide: NADCA Standards and Practical Limits
Overview
Tolerance is where die casting programs lose money quietly. A drawing dimensioned to ±0.05 mm everywhere forces the supplier into 100% inspection, accelerated die wear and scrap that no one budgeted for. The NADCA Product Specification Standards give two linear tolerance classes — Class 1 (premium) and Class 2 (commercial) — that reflect what a well-maintained die casting machine and tool can hold repeatably. Features split by the parting line, or controlled by a moving die component (slider, core, unscrewing device), cannot hold the same numbers and must be toleranced separately.
This reference lists the practical limits most often mis-specified: linear dimensions, parting-line and moving-die-component variation, draft angles, and wall thickness. Values below are representative of aluminum HPDC; zinc holds tighter and magnesium sits between. Confirm against the controlling NADCA specification before release.
Linear Tolerances (Aluminum, Approximate)
| Dimension (mm) | Class 1 ± (mm) | Class 2 ± (mm) |
|---|---|---|
| 0 - 25 | 0.10 | 0.15 |
| 25 - 50 | 0.13 | 0.20 |
| 50 - 100 | 0.18 | 0.28 |
| 100 - 200 | 0.30 | 0.43 |
| 200 - 400 | 0.55 | 0.75 |
Parting-Line and Moving-Die-Component Tolerances
| Feature type | Typical ± (mm) | Note |
|---|---|---|
| Parting-line mismatch (flat) | 0.10 - 0.15 | Per side of shutoff |
| Parting-line mismatch (perpendicular) | 0.15 - 0.25 | Step at parting line |
| Slider / core (moving die) | 0.13 - 0.25 | Worse with wear |
| Ejector-pin witness | 0.05 - 0.15 | Bump height, not a dimension |
Draft Angles and Wall Thickness
| Parameter | Practical range | Recommended |
|---|---|---|
| External draft | 1° - 3° | 2° |
| Internal / core draft | 2° - 5° | 3° |
| Textured surfaces (add) | +1° - 2° | — |
| Wall thickness (typical) | 1.5 - 4.0 mm | 2.0 - 3.0 mm |
| Wall thickness (thin, achievable) | 0.8 - 1.2 mm | local only |
How to use this reference
- Dimension only what functions. Apply Class 2 (commercial) as the default and reserve Class 1 for fit and seal features.
- Never tolerance a parting-line-split diameter to Class 1. Split it into two half-features or accept the parting-line band.
- Give moving-die features (slides, cores) their own looser callout; do not co-locate a tight tolerance with a slider.
- Hold draft to the recommended values. Removing draft to hit a cosmetic flat forces abrasive stripping that wears the tool.
- Keep nominal walls in the 2.0-3.0 mm band. Pushing below 1.2 mm raises cold-shut and short-fill risk — see Die Casting DFM Guidelines.
- For machined features, switch to ISO 2768 or CNC limits — see Tolerances and GD&T.
Related Articles
- Die Casting DFM Guidelines
- Die Casting vs Sand vs Gravity Casting
- Tolerances and GD&T
- Surface Treatment and Coatings
References
- NADCA Product Specification Standards for Die Castings — https://www.diecasting.org/
- ISO 2768-1, General tolerances for linear and angular dimensions