ISO 2768 / ISO 286
CNC Machining
Ref: ISO 2768, ISO 286, DIN 7150CNC milling and turning offer the widest range of achievable tolerances of any process. Tolerances depend heavily on machine quality, fixturing, thermal stability, tooling, and feature size.
| Tolerance Type | Standard | Typical | Precision | High Precision | Notes |
|---|---|---|---|---|---|
| Linear dimension (±) | ±0.1 mm | ±0.05 mm | ±0.01 mm | ±0.005 mm | Tighter requires temperature-controlled environment |
| Hole diameter (H7) | IT8 | IT7 | IT6 | IT5 | Reaming required for IT6 and below |
| Shaft diameter (h6) | IT8 | IT7 | IT6 | IT5 | Grinding required for IT5 |
| Flatness (per 100 mm) | 0.05 mm | 0.02 mm | 0.005 mm | 0.001 mm | Precision requires surface grinding |
| Perpendicularity | 0.05 mm | 0.02 mm | 0.005 mm | 0.002 mm | Per 100 mm |
| Parallelism | 0.05 mm | 0.02 mm | 0.005 mm | 0.002 mm | Per 100 mm; fixturing critical |
| Angular tolerance | ±0°30′ | ±0°10′ | ±0°2′ | ±0°1′ | 5-axis machining improves compound angles |
| Positional (hole pattern) | ±0.05 mm | ±0.02 mm | ±0.01 mm | ±0.005 mm | True position tolerance (∅ zone) |
| Thread pitch (ISO) | Class 6H/6g standard | Class 5H/5g | Class 4H/4g | Tap drill and tap condition critical | |
| Surface roughness Ra | 3.2 µm | 1.6 µm | 0.8 µm | 0.4 µm | Ra 0.4 requires sharp CBN/diamond tooling |
DIN 6930 / EN 13715
Sheet Metal Fabrication
Ref: DIN 6930, DIN 6935, ISO 2768Sheet metal tolerances vary significantly between cutting, bending, and hole operations. DIN 6930 governs punched and sheared parts; DIN 6935 governs bending. Tolerances tighten with sheet thickness.
| Feature / Operation | Economy | Standard | Precision | Notes |
|---|---|---|---|---|
| CUTTING (Laser, Punch, Waterjet) | ||||
| External profile (±) | ±0.5 mm | ±0.2 mm | ±0.1 mm | Laser: ±0.1mm; punch: ±0.2mm; plasma: ±0.5mm |
| Hole diameter (±) | ±0.3 mm | ±0.1 mm | ±0.05 mm | Min hole dia = 1× sheet thickness |
| Hole position (±) | ±0.3 mm | ±0.15 mm | ±0.05 mm | Laser punching: ±0.1mm typical |
| Edge straightness (per 100mm) | 0.5 mm | 0.2 mm | 0.1 mm | Laser improved by assist gas |
| BENDING (Press Brake) | ||||
| Bend angle (±) | ±2° | ±1° | ±0.5° | Springback compensation critical; material-dependent |
| Flange length (±) | ±0.5 mm | ±0.3 mm | ±0.1 mm | From bend centre line |
| Min bend radius | 1× t (soft Al, mild steel) | 0.5× t | t = sheet thickness; harder alloys need larger R | |
| Flatness after bend | 1.5 mm/m | 0.5 mm/m | 0.2 mm/m | Depends on springback and material thickness |
| FORMING & ASSEMBLY | ||||
| Overall assembly (±) | ±1.0 mm | ±0.5 mm | ±0.2 mm | Cumulative from multiple bends |
| Countersink / counterbore (±) | ±0.3 mm | ±0.15 mm | ±0.05 mm | CNC punching; depth controlled by punch travel |
ISO 8062 / DIN 1684
Casting Tolerances
Ref: ISO 8062-3 (Dimensional tolerances), DIN 1684 (sand casting)ISO 8062-3 defines Casting Tolerance grades (CT) from CT1 to CT16. Lower CT = tighter tolerance. Each casting process has an achievable CT range. All functional surfaces require machining unless explicitly designed to be as-cast.
| Casting Process | CT Grade Range | Achievable Linear (±mm) at 100mm | Surface Ra (µm) | Notes |
|---|---|---|---|---|
| Investment / Lost Wax | CT4–CT6 | ±0.26–0.50 | 1.6–6.3 | Best near-net shape; complex geometries; aerospace |
| Die Casting (pressure) | CT4–CT7 | ±0.26–0.64 | 0.8–3.2 | High volume; excellent surface; Al/Zn/Mg alloys |
| Permanent Mold / Gravity Die | CT6–CT9 | ±0.50–1.30 | 3.2–12.5 | Medium volume; better than sand |
| Shell Mold Casting | CT5–CT8 | ±0.38–1.00 | 3.2–12.5 | Better surface than green sand |
| Green Sand Casting (machine) | CT8–CT12 | ±1.00–3.20 | 6.3–25 | Most economical; ferrous and non-ferrous |
| Green Sand Casting (hand) | CT11–CT14 | ±2.60–6.40 | 12.5–50 | Low volume; prototype; large parts |
| Lost Foam Casting | CT8–CT10 | ±1.00–2.00 | 6.3–25 | Complex shapes; automotive blocks |
| Centrifugal Casting | CT8–CT11 | ±1.00–2.60 | 6.3–25 | Pipes, rings, cylinders; OD better than ID |
| CT Grade | up to 25 mm | 25–63 mm | 63–160 mm | 160–400 mm | 400–1000 mm |
|---|---|---|---|---|---|
| CT4 | ±0.16 | ±0.20 | ±0.26 | ±0.32 | ±0.42 |
| CT5 | ±0.22 | ±0.28 | ±0.36 | ±0.46 | ±0.58 |
| CT6 | ±0.32 | ±0.40 | ±0.50 | ±0.64 | ±0.82 |
| CT7 | ±0.44 | ±0.56 | ±0.72 | ±0.90 | ±1.14 |
| CT8 | ±0.62 | ±0.80 | ±1.00 | ±1.28 | ±1.60 |
| CT9 | ±0.88 | ±1.12 | ±1.40 | ±1.80 | ±2.24 |
| CT10 | ±1.24 | ±1.60 | ±2.00 | ±2.52 | ±3.20 |
| CT11 | ±1.76 | ±2.24 | ±2.80 | ±3.52 | ±4.48 |
| CT12 | ±2.48 | ±3.20 | ±4.00 | ±5.04 | ±6.40 |
ISO 20457 / DIN 16742
Injection Molding Tolerances
Ref: ISO 20457, DIN 16742Injection molding tolerances depend on material (shrinkage), part geometry, wall thickness, gate location, and mold quality. ISO 20457 supersedes DIN 16742. Tolerances are specified as tolerance classes T1 (tight) through T5 (loose).
| Tolerance Class | up to 18 mm | 18–50 mm | 50–120 mm | 120–315 mm | Application |
|---|---|---|---|---|---|
| T1 — Precision | ±0.05 | ±0.08 | ±0.12 | ±0.20 | Precision optics, medical devices; validated tool + material |
| T2 — Fine | ±0.08 | ±0.12 | ±0.20 | ±0.32 | Precision consumer electronics, connectors |
| T3 — Standard | ±0.12 | ±0.20 | ±0.32 | ±0.50 | Most industrial parts; standard tooling |
| T4 — Commercial | ±0.20 | ±0.32 | ±0.50 | ±0.80 | Consumer goods; relaxed requirements |
| T5 — Coarse | ±0.32 | ±0.50 | ±0.80 | ±1.25 | Large parts; high shrinkage materials; non-critical |
| Material | Shrinkage (%) | Notes |
|---|---|---|
| ABS | 0.4–0.9% | Low, consistent — good for precision parts |
| PC (Polycarbonate) | 0.5–0.7% | Low and consistent; optical applications |
| PA6 (Nylon 6) | 0.8–1.5% | Hygroscopic; moisture changes dimensions post-mold |
| PA66 (Nylon 66) | 1.0–2.0% | Higher shrinkage; directional (flow vs transverse) |
| PP (Polypropylene) | 1.5–2.5% | High and variable; avoid tight tolerances |
| HDPE | 2.0–4.0% | Very high; poor tolerance capability |
| POM (Acetal / Delrin) | 1.8–2.5% | Good stability after initial shrinkage |
| PEEK | 0.1–0.5% | Very low; excellent for precision; high cost |
| GF-reinforced PA66 | 0.3–0.8% | Glass reduces shrinkage significantly; anisotropic |
| GF-reinforced PP | 0.4–1.0% | Better tolerance than unfilled PP |
ISO 10243 / DIN 7526
Forging Tolerances
Ref: ISO 10243 (closed die), DIN 7526, EN 10243-1Forging tolerances depend on part weight, material, die complexity, and whether the operation is hot or cold. EN 10243-1 defines tolerance grades for steel die forgings (E, F, G classes). Functional surfaces always require subsequent machining.
| Process / Grade | Linear Tolerance (±mm) at 100mm | Die Parting Offset (mm) | Flatness (mm/m) | Notes |
|---|---|---|---|---|
| Hot Forging — Grade E (fine) | ±0.8 | 0.4 | 5 | Trimmed, corrected; precision applications |
| Hot Forging — Grade F (normal) | ±1.2 | 0.6 | 7 | Standard production; most common |
| Hot Forging — Grade G (coarse) | ±1.8 | 1.0 | 10 | Complex shapes; high die wear |
| Cold Forging / Coining | ±0.1–0.3 | 0.1 | 1 | Near-net shape; limited to softer alloys and small parts |
| Precision Forging (net-shape) | ±0.2–0.5 | 0.2 | 2 | Titanium aerospace gears; expensive tooling |
| Roll Forging | ±1.0–2.0 | — | — | Shafts and bar profiles; elongated parts |
ISO 13920 / EN ISO 13920
Welded Structure Tolerances
Ref: ISO 13920, ISO 2768, AWS D1.1ISO 13920 defines general tolerances for welded constructions on linear and angular dimensions, and for form and position. Four tolerance classes: A (fine), B (medium), C (coarse), D (very coarse). Separate from weld joint quality (see Welding Reference page).
| Class | 30–120 mm | 120–400 mm | 400–1000 mm | 1000–2000 mm | 2000–4000 mm | >4000 mm |
|---|---|---|---|---|---|---|
| A — Fine | ±1 | ±1 | ±2 | ±3 | ±4 | ±5 |
| B — Medium | ±1 | ±2 | ±3 | ±4 | ±6 | ±8 |
| C — Coarse | ±2 | ±3 | ±5 | ±7 | ±10 | ±14 |
| D — Very Coarse | ±3 | ±5 | ±8 | ±11 | ±16 | ±22 |
| Class | Angular (per 1000 mm) | Straightness / Flatness (per 1000 mm) |
|---|---|---|
| A — Fine | ±2 mm | ±2 mm |
| B — Medium | ±3 mm | ±4 mm |
| C — Coarse | ±6 mm | ±8 mm |
| D — Very Coarse | ±10 mm | ±16 mm |
ISO/ASTM 52900
Additive Manufacturing Tolerances
Ref: ISO/ASTM 52910, ISO/ASTM 52900AM tolerances vary dramatically by process, material, machine, and part geometry. As-built tolerances are typically insufficient for functional fits — post-machining is standard for bearing surfaces, threads, and precision holes.
| Process | Typical XY (±mm) | Typical Z (±mm) | Min Feature (mm) | Surface Ra (µm) | Notes |
|---|---|---|---|---|---|
| SLA (Resin) | ±0.1 | ±0.1 | 0.2 | 0.8–3.2 | Best accuracy of polymer AM; Z layers visible |
| DLP / MSLA | ±0.1–0.2 | ±0.1 | 0.2 | 0.8–3.2 | Similar to SLA; pixelation visible at edges |
| FDM / FFF | ±0.2–0.5 | ±0.2–0.5 | 0.8 | 6.3–50 | Layer lines prominent; anisotropic strength |
| MJF / SLS (Nylon) | ±0.2–0.3 | ±0.2–0.3 | 0.5 | 6.3–12.5 | No supports needed; good for interlocking parts |
| SLM / DMLS (Metal) | ±0.1–0.2 | ±0.1–0.2 | 0.3 | 6.3–25 | Thermal distortion; support removal marks |
| EBM (Ti/Inconel) | ±0.2–0.5 | ±0.2–0.5 | 0.5 | 12.5–50 | Powder partially sintered; requires blasting |
| LENS / DED | ±0.5–1.0 | ±0.3–0.5 | 1.0 | 12.5–50 | Near-net shape; machining always required |
| Binder Jetting (Metal) | ±0.3–0.5 | ±0.3–0.5 | 0.4 | 3.2–12.5 | Sintering shrinkage ~15–20%; must be calibrated |
DIN 8580 / Industry Practice
EDM Tolerances
Ref: DIN 8580, industry standards| Process | Dimensional (±mm) | IT Grade | Surface Ra (µm) | Notes |
|---|---|---|---|---|
| Wire EDM (rough) | ±0.01–0.02 | IT6–IT7 | 1.6–3.2 | Single pass; fast |
| Wire EDM (precision) | ±0.003–0.005 | IT4–IT5 | 0.4–0.8 | 3–4 trim passes; slow |
| Sinker EDM (standard) | ±0.01–0.05 | IT6–IT8 | 1.6–6.3 | Electrode wear compensated |
| Sinker EDM (fine) | ±0.005–0.01 | IT5–IT6 | 0.4–1.6 | Fine finish settings; multiple electrodes |
| Micro EDM | ±0.002–0.005 | IT3–IT5 | 0.2–0.8 | Features below 0.5mm; watch/medical |
| ECM (Electrochemical) | ±0.02–0.1 | IT7–IT9 | 0.025–0.4 | No tool wear; very smooth; no recast layer |
EN 755 / EN 12020
Extrusion Tolerances
Ref: EN 755 (Al rod/tube), EN 12020 (precision Al), ISO 11960| Feature | Class A (Normal) | Class B (Precision) | Notes |
|---|---|---|---|
| Cross-section dimension ≤ 10 mm | ±0.3 mm | ±0.15 mm | Die precision and alloy affect achievable |
| Cross-section dimension 10–25 mm | ±0.4 mm | ±0.20 mm | 6000-series alloys best for extrusion tolerance |
| Cross-section dimension 25–100 mm | ±0.5 mm | ±0.25 mm | |
| Angular deviation | ±1.5° | ±1.0° | Between adjacent faces |
| Straightness (per metre) | 1.5 mm/m | 0.5 mm/m | Stretch straightening improves to 0.5mm/m |
| Wall thickness | ±10% | ±7% | Min wall = 1.0–2.0 mm depending on circumscribed circle |
| Length tolerance | +3/−0 mm | +2/−0 mm | Standard cut-to-length; saw cutting |
DfMA Summary
Quick Comparison — All Processes
A single-table overview for process selection at the conceptual design stage. Typical values for a ~100mm feature in a common structural material.
| Process | Typical Linear (±mm) | Best Achievable (±mm) | IT Grade (typical) | Ra Typical (µm) | Machining Required? |
|---|---|---|---|---|---|
| CNC Machining | ±0.05 | ±0.005 | IT7 | 1.6 | No (is machining) |
| Grinding | ±0.01 | ±0.001 | IT5–6 | 0.4 | No (is machining) |
| Sheet Metal | ±0.2 | ±0.05 | IT10 | 3.2 | Rarely |
| Die Casting | ±0.3 | ±0.1 | IT11 | 1.6 | For fits & threads |
| Investment Casting | ±0.5 | ±0.2 | IT11 | 3.2 | For fits & threads |
| Sand Casting | ±1.5 | ±0.8 | IT13 | 12.5 | Always for functions |
| Injection Molding | ±0.3 | ±0.05 | IT11 | 1.6 | Rarely |
| Hot Forging | ±1.2 | ±0.5 | IT13 | 12.5 | Always for functions |
| Cold Forging | ±0.2 | ±0.05 | IT10 | 3.2 | For precision fits |
| Welded Structure | ±1.5 | ±0.5 | — | 6.3 | For precision features |
| SLM Metal Print | ±0.15 | ±0.05 | IT12 | 12.5 | For fits & threads |
| FDM Plastic Print | ±0.3 | ±0.15 | IT13 | 12.5 | Usually not feasible |
| Wire EDM | ±0.01 | ±0.003 | IT5 | 0.8 | No (is machining) |
| Al Extrusion | ±0.4 | ±0.15 | IT11 | 3.2 | For precision features |
Tolerance Stack-Up Reminder
These are single-feature tolerances. When multiple features accumulate in an assembly, worst-case tolerance stack-up can easily exceed any individual tolerance. For assemblies, perform a proper 1D tolerance analysis (worst case or RSS) before committing to a process. The Tolerance Stack Analyzer tool (coming soon) covers this.