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0908191ef3
Complete ISO 286-1 skill for mechanical designers covering: - Fit selection (clearance/transition/interference) with intake protocol - IT grades 1–16 with required machining processes for bores and shafts - Full functional elements reference: rolling bearings, gears, keys (DIN 6885), Seeger rings, cylindrical pins, plain bushings, lip seals, splined profiles, couplings, linear guides (14 sections total) - Fundamental deviations table (bores A–ZC, shafts a–zc, Ø1–500 mm) - Surface roughness Ra correlation by IT grade - Python calculator (scripts/calculate_fit.py) with JSON data files for exact clearance/interference computation and formatted fit data sheet output - Visual input support: analyses attached drawings, sketches, photos - Description ≤ 1024 chars, written in English for optimal trigger accuracy Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
6.1 KiB
6.1 KiB
IT Tolerance Grades — Manufacturing Processes and Applications
IT Grade Values by Diameter Range (µm, ISO 286-1)
| IT Grade | 1–3 mm | 3–6 mm | 6–10 mm | 10–18 mm | 18–30 mm | 30–50 mm | 50–80 mm | 80–120 mm | 120–180 mm | 180–250 mm |
|---|---|---|---|---|---|---|---|---|---|---|
| IT1 | 0.8 | 1 | 1 | 1.2 | 1.5 | 1.5 | 2 | 2.5 | 3.5 | 4.5 |
| IT2 | 1.2 | 1.5 | 1.5 | 2 | 2.5 | 2.5 | 3 | 4 | 5 | 7 |
| IT3 | 2 | 2.5 | 2.5 | 3 | 4 | 4 | 5 | 6 | 8 | 10 |
| IT4 | 3 | 4 | 4 | 5 | 6 | 7 | 8 | 10 | 12 | 14 |
| IT5 | 4 | 5 | 6 | 8 | 9 | 11 | 13 | 15 | 18 | 20 |
| IT6 | 6 | 8 | 9 | 11 | 13 | 16 | 19 | 22 | 25 | 29 |
| IT7 | 10 | 12 | 15 | 18 | 21 | 25 | 30 | 35 | 40 | 46 |
| IT8 | 14 | 18 | 22 | 27 | 33 | 39 | 46 | 54 | 63 | 72 |
| IT9 | 25 | 30 | 36 | 43 | 52 | 62 | 74 | 87 | 100 | 115 |
| IT10 | 40 | 48 | 58 | 70 | 84 | 100 | 120 | 140 | 160 | 185 |
| IT11 | 60 | 75 | 90 | 110 | 130 | 160 | 190 | 220 | 250 | 290 |
| IT12 | 100 | 120 | 150 | 180 | 210 | 250 | 300 | 350 | 400 | 460 |
| IT13 | 140 | 180 | 220 | 270 | 330 | 390 | 460 | 540 | 630 | 720 |
| IT14 | 250 | 300 | 360 | 430 | 520 | 620 | 740 | 870 | 1000 | 1150 |
Required Machining by IT Grade — Bores and Shafts
Distinguishing bore vs. shaft is critical: achieving IT7 on a bore is significantly harder and more expensive than on a shaft, because bores cannot be externally cylindrically ground.
| IT Grade | Machining for BORES | Machining for SHAFTS | Difficulty | Relative cost |
|---|---|---|---|---|
| IT3–IT4 | Precision honing, lapping | Ultra-precision cylindrical grinding, lapping | Extreme | ★★★★★ |
| IT5 | Precision boring (single-blade), fine honing | Precision cylindrical grinding (Ra 0.2) | Very high | ★★★★☆ |
| IT6 | Fine CNC boring (single-blade tool), internal grinding | Standard cylindrical grinding | High | ★★★☆☆ |
| IT7 | CNC boring with adjustable insert, fine internal turning | Fine CNC turning (high Vc, low feed), grinding | Medium | ★★☆☆☆ |
| IT8 | Standard drilling + reaming, internal turning | Standard CNC turning | Low | ★★☆☆☆ |
| IT9 | Drilling with sharp bits, rough internal turning | Standard turning | Very low | ★☆☆☆☆ |
| IT10–IT11 | Standard drilling, punching | Rough turning, milling | Minimal | ★☆☆☆☆ |
| IT12–IT14 | Shell casting, stamping | Forging, sand casting | — | ★☆☆☆☆ |
Operational notes by IT grade
IT5–IT6 (high precision)
- Bores: single-blade boring is the reference process. Requires rigid fixture, carbide tool, correct coolant. Alternative: internal grinding (more expensive, requires dedicated machine).
- Shafts: between-centers or collet cylindrical grinding. Freshly dressed wheel, active thermal compensation.
- Minimum equipment: rigid machining centre (≥15kN spindle), in-process gauging recommended.
IT7 (standard reference grade)
- Bores: CNC boring with adjustable insert (e.g. Sandvik CoroBore, Kennametal). Standard drilling alone does not reliably achieve IT7. Economic alternative: pilot drill + machine reamer with calibrated reamer (IT7 guaranteed).
- Shafts: fine turning with wiper insert. On modern CNC, IT7 is routine. Watch out: long chips or gummy materials (stainless steel, construction aluminium) tend to drift to IT8.
- Inspection: go/no-go plug gauge for bores, ring gauge or micrometer for shafts. Measure after the part has cooled.
IT8 (standard production)
- Achievable with standard turning and drilling — no special equipment.
- Suitable for keyways, non-critical sliding bushings, loose fits.
IT9–IT11 (free tolerances)
- Standard for non-functional dimensions. Covered by ISO 2768-m (IT11) general tolerances.
Manufacturing Processes and Achievable IT Grades
| Manufacturing process | Typical IT grades | Notes |
|---|---|---|
| Lapping / superfinishing | IT3 – IT5 | Extreme finishes, small parts |
| Precision honing | IT4 – IT6 | Cylinders, engine bore |
| Precision cylindrical grinding | IT4 – IT6 | High-precision shafts, spindles |
| Standard cylindrical grinding | IT5 – IT7 | Transmission shafts, bearing seats |
| Fine turning / diamond | IT5 – IT7 | Non-ferrous alloys, bronze, aluminium |
| Precision boring (single-blade) | IT5 – IT7 | High-precision bores |
| Internal grinding | IT5 – IT7 | Large diameter bores |
| CNC boring (adjustable insert) | IT6 – IT8 | Standard coupling bores |
| Fine CNC turning (wiper insert) | IT6 – IT8 | Standard functional shafts |
| EDM | IT5 – IT8 | Dies, complex forms |
| Standard CNC turning | IT7 – IT9 | Production standard |
| Standard reaming / drill + ream | IT8 – IT10 | Non-critical bores |
| CNC milling | IT8 – IT10 | Planes, profiles, slots |
| Standard drilling | IT10 – IT12 | Through holes, fasteners |
| Stamping / blanking | IT10 – IT12 | Sheet metal |
| Shell moulding | IT11 – IT14 | Precision castings |
| Sand casting | IT14 – IT16 | Raw castings |
| Forging | IT14 – IT16 | Semi-finished stock |
Grade Selection Guidelines
IT01 – IT4
- Measuring instruments, gauge blocks, reference standards
- Ultra-precision bearings (class P4, P2)
- Practically unused in standard mechanical production
- Very high cost, requires controlled environments
IT5 – IT6
- High-precision fits: machine tool spindles, precision shafts
- P6/P5 bearings
- Precision gears (ISO 1328 quality 5–7)
- High-pressure valve seats
- Grinding required
IT7
- The most widely used grade in industrial mechanics
- Functional shaft-bore fits (H7/k6, H7/g6, H7/h6, etc.)
- Standard bearing housing bores (class P0/P6)
- Fine turning or CNC boring on modern machines
IT8
- Less critical fits, larger clearances
- Keyways, key slots
- Non-critical sliding bushings
- Good-quality standard turning
IT9 – IT10
- Non-coupled components
- Thicknesses, lengths, non-functional positions
- High-quality free dimensions (ISO 2768-f, -m)
IT11 – IT14
- Standard free tolerances (ISO 2768-c, -v)
- General tolerances on drawings
- Non-functional distances, clearances, spaces