Guided by YB Metal (Suzhou, China), GD&T for castings — green sand, resin/no-bake & shell molding under one roof, plus machining, simulation-led gating/risers, and traceable QA.
Excerpt: Casting drawings mix as-cast and machined features. This guide shows how to set GD&T (flatness, position, profile) that matches process capability—so parts pass first time without over-specifying cost.
Table of contents
- Castings + GD&T: the mindset
- Pick the right datums (stack-friendly)
- Capability: as-cast vs machined (start values)
- Flatness, position & profile — practical callouts
- Drawing & RFQ notes (copy-paste)
- Inspection plan (what to measure, when)
- FAQs
Castings + GD&T: the mindset
- Separate what is as-cast from what is machined.
- Tie functional features to a machined datum scheme where possible; avoid relying on raw, unstable surfaces as primary datums.
- Match tolerances to process capability (ISO 8062-3 CT grades for as-cast; machining capability for finished faces).
Pick the right datums (stack-friendly)
Table A — Datum schemes that work for iron castings
| Use case | Primary (A) | Secondary (B) | Tertiary (C) | Notes |
|---|---|---|---|---|
| Mounting face + bolt pattern | Machined mounting plane | Machined Ø bore or pilot | Bolt hole @ MMC | Robust: assembly sits on A; B locks rotation; C clocks pattern |
| Pump/gearbox housing | Machined seal face | Main bearing bore | Cross bore or pad | Locates shaft centerline; good for leak-tight bosses |
| As-cast datum needed | Best as-cast pad/plane | Machined pilot | Secondary machined face | Use only if no machined plane exists; keep tolerances generous |
Tip: Avoid making a cored hole a datum feature for assembly unless it is finish-machined.
Capability: as-cast vs machined (start values)
Indicative ranges. Confirm with your foundry/machine shop. CT = ISO 8062-3 casting tolerance grade. Units in mm (in).
Table B — Flatness & profile starters by process
| Feature / Process | Green sand (CT9–CT10) | Resin/no-bake (CT8–CT9) | Shell (CT6–CT7) |
|---|---|---|---|
| As-cast flatness ≤100 mm (3.9 in) | 0.3–0.6 (0.012–0.024) | 0.2–0.5 (0.008–0.020) | 0.15–0.3 (0.006–0.012) |
| As-cast flatness 100–300 mm (3.9–11.8 in) | 0.5–1.0 (0.020–0.039) | 0.3–0.8 (0.012–0.031) | 0.25–0.6 (0.010–0.024) |
| As-cast profile (total band) | 1.0–2.0 | 0.6–1.5 | 0.4–1.0 |
| Machined flatness ≤100 mm | 0.05–0.10 (0.002–0.004) | — | — |
| Machined flatness 100–300 mm | 0.08–0.20 (0.003–0.008) | — | — |
Table C — Position tolerance starters (holes, relative to A|B(M)|C(M))
| Hole Ø (mm) | Typical function | Position @ MMC (mm) | Position @ RFS (mm) |
|---|---|---|---|
| ≤10 (≤0.39 in) | Fasteners, dowels | 0.10–0.20 | 0.15–0.25 |
| >10–20 (0.39–0.79 in) | Bolts, studs | 0.15–0.30 | 0.25–0.40 |
| >20–40 (0.79–1.57 in) | Through bolts, ports | 0.25–0.50 | 0.35–0.70 |
| Cored holes (as-cast) | Flow/vent, non-locating | 0.5–1.0 | 0.8–1.5 |
Use MMC (⟂ with M modifier) on holes when assembly has clearance; it gives bonus tolerance that reduces scrap without hurting fit.
Drawing & RFQ notes（copy-paste）
Table D — Notes that save cost and pain
| Topic | Copy-paste note |
|---|---|
| Process & CT | Casting route: Green sand (or Resin/Shell). Target ISO 8062-3 CT9 (or CT8/CT6) for as-cast geometry. |
| Datum policy | Functional features to be related to machined datums where possible. As-cast datums used only when no machined datum exists. |
| Flatness | As-cast flatness per Table B. Machined flatness 0.05–0.20 mm by size. |
| Position | Machined holes use MMC where clearance allows. Cored holes are non-locating unless noted. |
| Profile | *As-cast external surfaces: profile 1.0–2.0 mm (process-dependent), relative to A |
| Stock & finish | Machining allowance per mass range; machined faces Ra 3.2–6.3 μm (125–250 μin). |
| Inspection pack | Provide CMM report for criticals, hardness/chemistry certs, and leak/NDT if applicable. |
Inspection plan（what to measure, when）
Table E — Sample plan for pilot runs
| Item | Method | Frequency |
|---|---|---|
| Datums A/B/C | CMM | 100% at FAI, then 1/shift |
| Flatness (machined) | CMM/sweep indicator | 5 pcs/lot |
| Position (machined holes) | CMM | 5 pcs/lot (capability to Cpk ≥ 1.33) |
| Profile (as-cast) | CMM point cloud / templates | 5 pcs/lot |
| Leak test (if housing) | Air 0.8–1.5 bar, 30–60 s | 100% through T1 |
| Visual | AQL | Each lot |
Why YB Metal for drawing + GD&T execution
- One roof: green sand/resin/shell + machining
- Simulation-led risers/chills & datum feasibility reviews
- CMM reports tied to serials; leak/NDT evidence on pilot runs
FAQs
CTA — set tolerances you can defend
YBmetal quotes with process capability, profile/flatness/position recommendations, and pilot-run evidence—so engineering and SQE sign off faster.