{ "slug": "standard-tolerances", "title": "General Tolerances for CNC Parts: ISO 2768 and IT Grades", "description": "ISO 2768 general tolerances in four precision classes, IT grades IT01 to IT18, and what each CNC process holds — with the class to put on your drawing.", "lang": "en", "tables": [ { "caption": "ISO 2768-1 general tolerances for linear dimensions (mm)", "columns": [ "Nominal size range (mm)", "ISO 2768-f", "ISO 2768-m", "ISO 2768-c", "ISO 2768-v" ], "rows": [ { "Nominal size range (mm)": "0.5 – 3", "ISO 2768-f": "±0.05", "ISO 2768-m": "±0.1", "ISO 2768-c": "±0.2", "ISO 2768-v": "—" }, { "Nominal size range (mm)": "3 – 6", "ISO 2768-f": "±0.05", "ISO 2768-m": "±0.1", "ISO 2768-c": "±0.3", "ISO 2768-v": "±0.5" }, { "Nominal size range (mm)": "6 – 30", "ISO 2768-f": "±0.1", "ISO 2768-m": "±0.2", "ISO 2768-c": "±0.5", "ISO 2768-v": "±1.0" }, { "Nominal size range (mm)": "30 – 120", "ISO 2768-f": "±0.15", "ISO 2768-m": "±0.3", "ISO 2768-c": "±0.8", "ISO 2768-v": "±1.5" }, { "Nominal size range (mm)": "120 – 400", "ISO 2768-f": "±0.2", "ISO 2768-m": "±0.5", "ISO 2768-c": "±1.2", "ISO 2768-v": "±2.5" }, { "Nominal size range (mm)": "400 – 1000", "ISO 2768-f": "±0.3", "ISO 2768-m": "±0.8", "ISO 2768-c": "±2.0", "ISO 2768-v": "±4.0" }, { "Nominal size range (mm)": "1000 – 2000", "ISO 2768-f": "±0.5", "ISO 2768-m": "±1.2", "ISO 2768-c": "±3.0", "ISO 2768-v": "±6.0" }, { "Nominal size range (mm)": "2000 – 4000", "ISO 2768-f": "—", "ISO 2768-m": "±2.0", "ISO 2768-c": "±4.0", "ISO 2768-v": "±8.0" } ] }, { "caption": "Which Precision Class to Specify", "columns": [ "Class", "Precision level", "Typical use", "Cost impact" ], "rows": [ { "Class": "f (fine)", "Precision level": "Highest general", "Typical use": "Precision parts, mating surfaces not requiring a specific fit, tight cosmetic requirements", "Cost impact": "+15–30% vs medium" }, { "Class": "m (medium)", "Precision level": "Standard CNC", "Typical use": "General CNC machined parts. The most widely used class, suitable for the majority of machined components.", "Cost impact": "Baseline" }, { "Class": "c (coarse)", "Precision level": "Relaxed", "Typical use": "Sheet metal parts, structural weldments, non-critical castings, large assemblies", "Cost impact": "−10–20% vs medium" }, { "Class": "v (very coarse)", "Precision level": "Most relaxed", "Typical use": "Welded structures, rough castings, non-precision fabricated parts, very large dimensions", "Cost impact": "−20–35% vs medium" } ] }, { "caption": "IT Grades — What a Tolerance Number Means", "columns": [ "IT grade", "Practical meaning", "1–3 mm", "6–10 mm", "18–30 mm", "50–80 mm", "120–180 mm", "250–315 mm" ], "rows": [ { "IT grade": "IT01", "Practical meaning": "Gauge block reference", "1–3 mm": "0.3", "6–10 mm": "0.4", "18–30 mm": "0.6", "50–80 mm": "0.8", "120–180 mm": "1.0", "250–315 mm": "1.2" }, { "IT grade": "IT0", "Practical meaning": "Reference standard", "1–3 mm": "0.5", "6–10 mm": "0.6", "18–30 mm": "0.9", "50–80 mm": "1.2", "120–180 mm": "1.5", "250–315 mm": "2.0" }, { "IT grade": "IT1", "Practical meaning": "Precision gauge", "1–3 mm": "0.8", "6–10 mm": "1.0", "18–30 mm": "1.5", "50–80 mm": "2.0", "120–180 mm": "2.5", "250–315 mm": "3.0" }, { "IT grade": "IT2", "Practical meaning": "High-precision gauge", "1–3 mm": "1.2", "6–10 mm": "1.5", "18–30 mm": "2.5", "50–80 mm": "3.0", "120–180 mm": "4.0", "250–315 mm": "5.0" }, { "IT grade": "IT3", "Practical meaning": "Ultra-precision work", "1–3 mm": "2.0", "6–10 mm": "2.5", "18–30 mm": "4.0", "50–80 mm": "5.0", "120–180 mm": "6.0", "250–315 mm": "8.0" }, { "IT grade": "IT4", "Practical meaning": "Precision grinding / wire EDM", "1–3 mm": "3", "6–10 mm": "4", "18–30 mm": "6", "50–80 mm": "8", "120–180 mm": "10", "250–315 mm": "13" }, { "IT grade": "IT5", "Practical meaning": "Gauge manufacturing", "1–3 mm": "4", "6–10 mm": "6", "18–30 mm": "9", "50–80 mm": "13", "120–180 mm": "16", "250–315 mm": "20" }, { "IT grade": "IT6", "Practical meaning": "Precision machining", "1–3 mm": "6", "6–10 mm": "9", "18–30 mm": "13", "50–80 mm": "19", "120–180 mm": "25", "250–315 mm": "32" }, { "IT grade": "IT7", "Practical meaning": "Precision fit (bearings, shafts)", "1–3 mm": "10", "6–10 mm": "15", "18–30 mm": "21", "50–80 mm": "30", "120–180 mm": "40", "250–315 mm": "52" }, { "IT grade": "IT8", "Practical meaning": "General precision machining", "1–3 mm": "14", "6–10 mm": "22", "18–30 mm": "33", "50–80 mm": "46", "120–180 mm": "63", "250–315 mm": "81" }, { "IT grade": "IT9", "Practical meaning": "General machining (ISO 2768-m equivalent)", "1–3 mm": "25", "6–10 mm": "36", "18–30 mm": "52", "50–80 mm": "74", "120–180 mm": "100", "250–315 mm": "130" }, { "IT grade": "IT10", "Practical meaning": "Medium precision", "1–3 mm": "40", "6–10 mm": "58", "18–30 mm": "84", "50–80 mm": "120", "120–180 mm": "160", "250–315 mm": "210" }, { "IT grade": "IT11", "Practical meaning": "Loose machining", "1–3 mm": "60", "6–10 mm": "90", "18–30 mm": "130", "50–80 mm": "190", "120–180 mm": "250", "250–315 mm": "320" }, { "IT grade": "IT12", "Practical meaning": "Very rough machining", "1–3 mm": "100", "6–10 mm": "150", "18–30 mm": "210", "50–80 mm": "300", "120–180 mm": "400", "250–315 mm": "500" }, { "IT grade": "IT13", "Practical meaning": "Pattern and rough work", "1–3 mm": "140", "6–10 mm": "220", "18–30 mm": "310", "50–80 mm": "440", "120–180 mm": "580", "250–315 mm": "740" }, { "IT grade": "IT14", "Practical meaning": "Coarse, low-grade work", "1–3 mm": "250", "6–10 mm": "370", "18–30 mm": "520", "50–80 mm": "740", "120–180 mm": "1000", "250–315 mm": "1250" }, { "IT grade": "IT15", "Practical meaning": "Very coarse", "1–3 mm": "400", "6–10 mm": "600", "18–30 mm": "840", "50–80 mm": "1200", "120–180 mm": "1600", "250–315 mm": "2000" }, { "IT grade": "IT16", "Practical meaning": "Approximate / unspecified", "1–3 mm": "600", "6–10 mm": "1000", "18–30 mm": "1400", "50–80 mm": "2000", "120–180 mm": "2600", "250–315 mm": "3200" }, { "IT grade": "IT17", "Practical meaning": "Very approximate", "1–3 mm": "1000", "6–10 mm": "1600", "18–30 mm": "2400", "50–80 mm": "3300", "120–180 mm": "4300", "250–315 mm": "5300" }, { "IT grade": "IT18", "Practical meaning": "General fabricated work", "1–3 mm": "1400", "6–10 mm": "2500", "18–30 mm": "3500", "50–80 mm": "4800", "120–180 mm": "6300", "250–315 mm": "7600" } ] }, { "caption": "What Each CNC Process Actually Holds", "columns": [ "Process", "Standard (typical)", "Precision (extra cost)", "Ultra-precision (high cost)", "IT equivalent" ], "rows": [ { "Process": "CNC Milling (3-axis)", "Standard (typical)": "±0.025mm", "Precision (extra cost)": "±0.005mm", "Ultra-precision (high cost)": "±0.002mm", "IT equivalent": "IT8 → IT5 → IT3" }, { "Process": "CNC Milling (5-axis)", "Standard (typical)": "±0.010mm", "Precision (extra cost)": "±0.005mm", "Ultra-precision (high cost)": "±0.002mm", "IT equivalent": "IT7 → IT5 → IT3" }, { "Process": "CNC Turning", "Standard (typical)": "±0.025mm", "Precision (extra cost)": "±0.005mm", "Ultra-precision (high cost)": "±0.002mm", "IT equivalent": "IT8 → IT5 → IT3" }, { "Process": "Swiss-Type Turning", "Standard (typical)": "±0.010mm", "Precision (extra cost)": "±0.005mm", "Ultra-precision (high cost)": "±0.002mm", "IT equivalent": "IT7 → IT5 → IT3" }, { "Process": "Surface Grinding", "Standard (typical)": "±0.005mm", "Precision (extra cost)": "±0.002mm", "Ultra-precision (high cost)": "±0.001mm", "IT equivalent": "IT5 → IT3 → IT2" }, { "Process": "Jig Boring", "Standard (typical)": "±0.010mm", "Precision (extra cost)": "±0.005mm", "Ultra-precision (high cost)": "±0.002mm", "IT equivalent": "IT7 → IT5 → IT3" }, { "Process": "Wire EDM", "Standard (typical)": "±0.010mm", "Precision (extra cost)": "±0.003mm", "Ultra-precision (high cost)": "±0.001mm", "IT equivalent": "IT7 → IT4 → IT2" }, { "Process": "Sinker EDM", "Standard (typical)": "±0.015mm", "Precision (extra cost)": "±0.005mm", "Ultra-precision (high cost)": "±0.002mm", "IT equivalent": "IT8 → IT5 → IT3" } ] } ] }