Quick Answer
ISO 8062-3 (Dimensional and Geometrical Tolerances for Castings) defines 16 casting tolerance grades from CT1 (tightest) to CT16 (coarsest), where Silica Sol Lost Wax Investment Casting routinely achieves CT4 to CT6 (±0.13 mm to ±0.40 mm on features under 100 mm), Shell Molding achieves CT6 to CT8, and Resin Sand Casting achieves CT8 to CT10. For functional bores, sealing faces, and bearing seats requiring tighter than CT4 (such as ISO 2768-m/f or IT6–IT7), OEM buyers specify ISO 8062 Required Machining Allowance (RMA Grade E–H, 0.5–3.5 mm per side) and finish-machine on 3/4/5-axis CNC centers to ±0.025 mm.
⚙ Engineering & Foundry Verification — Qingdao Yucheng (YCUMETAL) 34,000㎡ Pingdu Facility
All casting grades on this page are poured and machined in-house at our 34,000㎡ Pingdu foundry & CNC plant (400+ staff, IATF 16949 & ISO 9001 certified). Every heat is verified by Spectro optical emission spectrometry before pouring, with internal soundness and machined datums validated via Nikon XTH 320 industrial CT, Hexagon CMM, and Nikon metallographic microscopy.
Process Capability: Silica Sol Investment Casting (cavity accuracy ≤0.05 mm, min hole Ø0.3 mm, ISO 8062 CT4–CT6) • Shell Mold & Resin Sand Casting • 3/4/5-Axis CNC Machining (±0.025 mm, Ra 0.8–3.2 μm) • Upload STEP / IGS / PDF Drawing for Free DFM Review →
1. Process-to-Tolerance Mapping: Which ISO 8062 CT Grade Matches Each Casting Method?
Before placing a blanket tolerance note on a 2D drawing, match the Dimensional Casting Tolerance Grade (DCTG) to both the molding method and alloy family. At our 34,000㎡ Pingdu plant, we apply the following production capabilities across all 5 casting processes and CNC machining:
| Manufacturing Process at YCUMETAL | Stainless & Carbon Steel | Ductile & Gray Cast Iron | Aluminum & Copper Alloys | Typical As-Cast Surface Roughness (Ra) | Recommended RMA (Machining Stock / Side) |
|---|---|---|---|---|---|
| Silica Sol Investment Casting | CT5 – CT6 (Small features CT4) | CT5 – CT6 | CT4 – CT5 | Ra 1.6 – 3.2 μm | 0.5 – 1.5 mm (RMA Grade E) |
| Coated-Sand Shell Molding | CT7 – CT8 | CT6 – CT7 | CT6 – CT7 | Ra 6.3 – 12.5 μm | 1.0 – 2.5 mm (RMA Grade F) |
| Gravity / Low-Pressure Permanent Mold | — | — | CT5 – CT7 | Ra 3.2 – 6.3 μm | 0.8 – 2.0 mm (RMA Grade E–F) |
| Lost Foam Casting | CT7 – CT9 | CT7 – CT8 | CT6 – CT8 | Ra 6.3 – 12.5 μm | 1.5 – 3.0 mm (RMA Grade F–G) |
| Furan Resin Sand Casting | CT9 – CT11 | CT8 – CT10 | CT8 – CT9 | Ra 12.5 – 25 μm | 2.0 – 6.0 mm (RMA Grade G–H) |
| Post-Casting 3/4/5-Axis CNC Machining | ±0.015 – ±0.025 mm (IT6–IT7) | ±0.015 – ±0.025 mm | ±0.010 – ±0.025 mm | Ra 0.8 – 3.2 μm | Verified on Hexagon CMM |
2. Complete ISO 8062-3 Linear Dimensional Casting Tolerance Chart (CT4 to CT12 in mm)
The table below lists the total casting tolerance band (mm) per ISO 8062-3. For symmetrical bilateral tolerancing, divide the table value by 2 (for example, a 50 mm investment-cast dimension at CT5 has a total tolerance band of 0.36 mm, which equals ±0.18 mm):
| Nominal Cast Dimension (mm) | CT4 (Total / ±mm) | CT5 (Total / ±mm) | CT6 (Total / ±mm) | CT7 (Total / ±mm) | CT8 (Total / ±mm) | CT9 (Total / ±mm) | CT10 (Total / ±mm) | CT11 (Total / ±mm) | CT12 (Total / ±mm) |
|---|---|---|---|---|---|---|---|---|---|
| ≤ 10 mm | 0.18 (±0.09) | 0.26 (±0.13) | 0.36 (±0.18) | 0.50 (±0.25) | 0.70 (±0.35) | 1.0 (±0.50) | 1.5 (±0.75) | 2.0 (±1.0) | 2.8 (±1.4) |
| > 10 to 16 mm | 0.20 (±0.10) | 0.28 (±0.14) | 0.38 (±0.19) | 0.54 (±0.27) | 0.78 (±0.39) | 1.1 (±0.55) | 1.6 (±0.80) | 2.2 (±1.1) | 3.0 (±1.5) |
| > 16 to 25 mm | 0.22 (±0.11) | 0.30 (±0.15) | 0.42 (±0.21) | 0.58 (±0.29) | 0.82 (±0.41) | 1.2 (±0.60) | 1.7 (±0.85) | 2.4 (±1.2) | 3.2 (±1.6) |
| > 25 to 40 mm | 0.24 (±0.12) | 0.32 (±0.16) | 0.46 (±0.23) | 0.64 (±0.32) | 0.90 (±0.45) | 1.3 (±0.65) | 1.8 (±0.90) | 2.6 (±1.3) | 3.6 (±1.8) |
| > 40 to 63 mm | 0.26 (±0.13) | 0.36 (±0.18) | 0.50 (±0.25) | 0.70 (±0.35) | 1.00 (±0.50) | 1.4 (±0.70) | 2.0 (±1.00) | 2.8 (±1.4) | 4.0 (±2.0) |
| > 63 to 100 mm | 0.28 (±0.14) | 0.40 (±0.20) | 0.56 (±0.28) | 0.78 (±0.39) | 1.10 (±0.55) | 1.6 (±0.80) | 2.2 (±1.10) | 3.2 (±1.6) | 4.4 (±2.2) |
| > 100 to 160 mm | 0.30 (±0.15) | 0.44 (±0.22) | 0.62 (±0.31) | 0.88 (±0.44) | 1.20 (±0.60) | 1.8 (±0.90) | 2.5 (±1.25) | 3.6 (±1.8) | 5.0 (±2.5) |
| > 160 to 250 mm | 0.34 (±0.17) | 0.50 (±0.25) | 0.70 (±0.35) | 1.00 (±0.50) | 1.40 (±0.70) | 2.0 (±1.00) | 2.8 (±1.40) | 4.0 (±2.0) | 5.6 (±2.8) |
| > 250 to 400 mm | 0.40 (±0.20) | 0.56 (±0.28) | 0.78 (±0.39) | 1.10 (±0.55) | 1.60 (±0.80) | 2.2 (±1.10) | 3.2 (±1.60) | 4.4 (±2.2) | 6.2 (±3.1) |
| > 400 to 630 mm | — | 0.64 (±0.32) | 0.90 (±0.45) | 1.20 (±0.60) | 1.80 (±0.90) | 2.6 (±1.30) | 3.6 (±1.80) | 5.0 (±2.5) | 7.0 (±3.5) |
| > 630 to 1,000 mm | — | — | 1.00 (±0.50) | 1.40 (±0.70) | 2.00 (±1.00) | 2.8 (±1.40) | 4.0 (±2.00) | 6.0 (±3.0) | 8.0 (±4.0) |
3. VDG P690 vs ISO 8062 Equivalence (D1 / D2 / D3 Investment Casting Tolerances)
Many German and European automotive/robotics drawings still call out VDG Merkblatt P690 (D1, D2, D3) for investment castings. Here is how VDG P690 maps to ISO 8062-3 and our Pingdu silica sol investment casting line:
- VDG P690 D1 (General Investment Casting Tolerance): Equivalent to ISO 8062 CT6 — achieved as-cast on all standard dimensions without straightening fixtures.
- VDG P690 D2 (Selected Functional Cast Features): Equivalent to ISO 8062 CT5 — standard on YCUMETAL’s automated robotic shell-building line for features within a single die half.
- VDG P690 D3 (High-Precision Gauge/Coined Features): Equivalent to ISO 8062 CT4 — achieved on short dimensions (≤50 mm) or via hydraulic cold/warm coining gauges after heat treatment.
4. Four Rules to Prevent Datum Drift Between Foundry Tooling and CNC Fixturing
- Never Place As-Cast Locating Datums (A-B-C) Across a Parting Line or Gate Area: Dimensions that cross a mold parting line or wax-die split add parting-line shift. Keep primary CNC fixture targets on a single mold side (see Parting Surface Design for Castings).
- Size Machining Allowance (RMA) to Match Distortion, Not Just Surface Roughness: Long slender stainless steel investment castings (CF8M / CF8) experience thermal movement during 1,080°C water-quench solution annealing. Specify 1.0–1.5 mm RMA per side on spans >150 mm (see Machining Allowance for Castings).
- Separate As-Cast Notes from Machined GD&T Notes on Your 2D Print: State both general standards clearly in the title block: e.g., “Untoleranced Cast Surfaces: ISO 8062-3 – DCTG 5 – GCTG 4; Untoleranced Machined Surfaces: ISO 2768-mK.”
- Lock First-Piece CMM Datums Before Production Tooling Freeze: Read our Casting Tolerances Buyer Guide and CNC Machining Tolerances Guide for complete PPAP / FAI inspection workflows.
Frequently Asked Questions (FAQ)
What is a realistic ISO 8062 tolerance grade for stainless steel investment castings?
For silica sol lost wax investment castings in 304/CF8, 316/CF8M, and 17-4PH, ISO 8062 CT5 is the realistic engineering target for functional cast features within one wax-die cavity, and CT6 for overall envelope dimensions up to 300 mm. CT4 can be held on small features under 25 mm or with dedicated coining/straightening fixtures.
Why shouldn’t I apply ISO 2768-m to raw unmachined casting surfaces?
ISO 2768-m is a machining/metal-removal standard (±0.2 mm at 30–120 mm) that does not account for alloy solidification shrinkage, shell thermal expansion, or heat-treatment distortion. Applying ISO 2768-m globally to raw cast walls forces unnecessary 100% CNC profiling and inflates part cost by 40–200%. Use ISO 8062 CT5–CT6 on non-mating cast walls and apply ISO 2768-m/f only to CNC-machined datums and bores.
How much machining allowance (RMA) should I leave for CNC machining on castings?
Per ISO 8062-3, allow 0.5–1.5 mm per side (RMA Grade E) for silica sol investment castings, 1.0–2.5 mm (Grade F) for shell mold and gravity castings, and 2.0–6.0 mm (Grade G–H) for resin sand castings depending on largest envelope dimension.