IS 2102 : 2018General Tolerances for Dimensions and Geometrical Tolerances for Machined Parts

IS 2102 specifies general tolerances for dimensions and geometrical tolerances for machined parts — the GD&T (Geometric Dimensioning + Tolerancing) framework for engineering drawings of machined components. It governs how to specify acceptable variation in dimension, form, orientation, location, and runout of features.

Use IS 2102 when: - Preparing engineering drawings for machined components (gears, shafts, brackets, housings, fittings) - Procuring machined parts from external supplier - Quality acceptance of machined parts at delivery - Forensic investigation of part assembly issues (interference, gap) - Dimensional certification for ISI / NABL accreditation

IS 2102:2018 aligns with international ISO 2768-1 (general dimensional tolerances) and ISO 2768-2 (general geometrical tolerances). The four standard tolerance grades (Fine, Medium, Coarse, Very Coarse) match ISO classifications.

Why GD&T matters in construction: While IS 2102 is primarily for mechanical / manufacturing context, it also applies to civil construction: - Pre-fabricated steel — beam ends, gusset plates, bolt holes per drawing tolerance - Pre-cast concrete — bearing surface flatness, edge straightness, dimensional tolerance for fit - Steel reinforcement — bend bar geometry, lap length tolerance - MEP equipment — pipe sizing, fitting tolerance, valve stem alignment - Site equipment — formwork dimensions, scaffold component fit, metal door / window fits

For structural steel fabrication tolerances specifically, IS 7215 is the more direct reference; IS 2102 covers the broader machined-component tolerancing language.

IS 2102:2018 + ISO 2768-1 dimensional tolerance grades:

| Grade | Description | Typical use | |---|---|---| | f (fine) | Tightest tolerance | Precision machinery, hydraulic cylinders, bearings | | m (medium) | Standard tolerance | General machine parts, structural fitting | | c (coarse) | Loose tolerance | Heavy machinery, agricultural equipment | | v (very coarse) | Very loose | Rough castings, weldments |

Tolerance ranges (ISO 2768-1 numerical values, for reference):

| Nominal size (mm) | Fine (f) | Medium (m) | Coarse (c) | Very Coarse (v) | |---|---|---|---|---| | 0.5-3 | ±0.05 | ±0.1 | ±0.2 | ±0.5 | | 3-6 | ±0.05 | ±0.1 | ±0.3 | ±0.5 | | 6-30 | ±0.1 | ±0.2 | ±0.5 | ±1.0 | | 30-120 | ±0.15 | ±0.3 | ±0.8 | ±1.5 | | 120-400 | ±0.2 | ±0.5 | ±1.2 | ±2.5 | | 400-1000 | ±0.3 | ±0.8 | ±2.0 | ±4.0 | | 1000-2000 | ±0.5 | ±1.2 | ±3.0 | ±6.0 | | 2000-4000 | — | ±2.0 | ±4.0 | ±8.0 |

Applied to all dimensions on the drawing unless individually toleranced.

Geometrical tolerances (ISO 2768-2 + IS 2102): - Form tolerances (no datum needed): straightness, flatness, circularity, cylindricity - Orientation tolerances (need datum): parallelism, perpendicularity, angularity - Location tolerances (need datum): position, concentricity, symmetry - Runout tolerances (need datum): circular runout, total runout

Specifying on drawing: - Standard practice: title block specifies general tolerance grade (e.g., 'General tolerances per IS 2102 Grade m') + individual tolerances for critical dimensions - Critical dimensions get individual ± toleranced values; rest follows general grade

Selection of grade per application:

| Application | Recommended grade | |---|---| | Precision machinery (CNC, robotics) | Fine (f) | | Hydraulic / pneumatic cylinders | Fine (f) | | Standard machine elements | Medium (m) | | Welded structural components | Medium (m) | | Structural steel fabrication (IS 7215) | Medium (m) — adjusted by IS 7215 | | Pre-cast concrete | Coarse (c) (typical 5-10 mm tolerance on dimension) | | Heavy industrial equipment | Coarse (c) | | Rough castings, weldments | Very Coarse (v) |

Bolt hole tolerances: - Standard hole for M12 bolt: 13 mm hole (1 mm clearance) - Per IS 800 + IS 2102: hole tolerance Grade m typical (±0.2 mm) - For high-tolerance assembly: Grade f (±0.1 mm)

Pre-cast concrete dimension tolerances (IS 11447 / IS 11451): - Length: ±5 mm for member up to 3 m; ±10 mm beyond - Cross-section: ±3 mm for thickness ≤ 100 mm; ±5 mm for 100-500 mm - Flatness: ≤ 5 mm under 3 m straight edge

Structural steel weld tolerance: - Weld size (leg length): ±10 % nominal (per IS 822 / IS 9595:1992) - Weld throat thickness: per design + ± 1-2 mm

Reinforcement bar bend tolerances (IS 2502): - Bend angle: ±2° - Bend leg length: ±10 mm - Cover after binding: ±5 mm

Plate flatness (IS 2102 + IS 1730): - Tolerance per plate type and thickness; e.g., 6 mm plate ±2 mm flatness over 1 m

Surface roughness (Ra micrometres): - Machined surface (turned): Ra 1.6-3.2 µm - Ground surface: Ra 0.4-1.6 µm - Polished surface: Ra 0.1-0.4 µm - Superfinished: Ra 0.01-0.1 µm - IS 1716 — surface roughness specification

General principles: - Tighter tolerance = higher cost (machine setup, inspection time) - Use Grade m as default; Grade f only for critical fits; Grade c for non-fit dimensions - Specify tolerance only where it matters; rest follows general

• IS 2102 (Parts 1-5) — general tolerances multi-part series.
• IS 2102 Part 1 (this code) — general tolerances on linear and angular dimensions.
• IS 2102 Part 2 — geometrical tolerances on dimensions and geometry.
• IS 2102 Part 3-5 — specific tolerances for various applications.
• IS 7215:1974 — tolerances for fabrication of steel structures (for structural steel specifically).
• IS 11447 — code of practice for design and construction of post-tensioned segmentally erected box girder bridges (pre-cast tolerances).
• IS 11451 — code of practice for ground granulated blast-furnace slag manufactured products (precast tolerances).
• IS 1716 — surface roughness specification.
• IS 1730 — dimensions for steel plates, sheets, strips and flats.
• IS 1732 — dimensions for round and square steel bars.
• IS 1864 — dimensions of structural sections (channels).
• IS 808 — dimensions for hot-rolled steel beams, channels, angles, tees.
• ISO 2768 (Part 1, 2) — international counterpart.
• ISO 286 — international counterpart for limits and fits.
• ASME Y14.5 — American GD&T standard.
• IS 2202 (Part 1) — wooden flush door shutters (timber tolerances).
• IS 2502 — reinforcement bar bending (bar bend tolerance).

1. No tolerance specification on drawing. Manufacturer makes 'best effort'; assembly issues at site. Always specify general tolerance grade in title block. 2. All dimensions individually toleranced. Drawing becomes cluttered, harder to read. Use general grade + individual tolerance only for critical dimensions. 3. Tolerance grade too tight for cost-no-object. Grade f machining costs 2-3× Grade m for same component. Use justified grade. 4. No GD&T for assembled / interface fits. Two parts assemble at site; geometry tolerance critical. Specify per ISO 5459 / IS 2102 Part 2. 5. Weld tolerance mixed with machining tolerance. Welded structures have larger tolerance; machined components tighter. Don't apply same grade to both. 6. Inconsistent unit / scale of dimensions. mm vs metres on same drawing. Standardise. 7. No reference datum specified for orientation / location tolerance. Datum is essential for these; without it, tolerance meaningless. 8. Tolerance stack-up not analysed. Multiple toleranced dimensions in series; total tolerance stack > individual. Use worst-case or statistical analysis. 9. Inspection method not specified. Different gauges give different readings; ambiguous. Specify inspection method (CMM / GO-NoGo gauge / dial gauge / etc.). 10. Surface roughness not specified for fitting surfaces. Bearing surfaces, sliding surfaces, sealing surfaces — all need roughness spec; IS 1716. 11. Wrong fit class for assembly. H7/g6 for sliding fit; H7/p6 for press fit; getting wrong fit class = assembly fails. Per ISO 286 / IS 1717. 12. No allowance for thermal expansion in tolerance design. Steel-aluminium bolted joint has differential expansion; clearance must account for temperature range.

Engineering drawing + procurement cascade:

1. Component design — function, fit, manufacturability. 2. Tolerance analysis: - Identify critical fits + interfaces - Apply GD&T per IS 2102 / ISO 2768 - Tolerance stack-up analysis for assemblies 3. Drawing creation: - General tolerance per IS 2102 grade specified in title block - Critical dimensions individually toleranced - GD&T frames for orientation / location / form / runout - Surface roughness symbols per IS 1716 4. Drawing release — design review + approval. 5. Procurement: - RFP / RFQ to suppliers - Drawing as basis for manufacturing - Acceptance criteria explicit (tolerance grade, GD&T, inspection method) 6. Manufacturing — supplier produces per drawing. 7. Quality inspection at delivery: - CMM measurement of critical dimensions - Surface roughness verification - GD&T verification - First-Article Inspection (FAI) report for new product 8. Assembly — verify fit + function on assembly. 9. Documentation — inspection records archived for traceability.

Design ratio (typical): - 80 % of dimensions follow general tolerance (Grade m for typical, Grade c for non-critical) - 15 % need individual tolerance - 5 % critical (Grade f or tighter, with GD&T)

IS 2102 is one of the foundational drafting standards; modern GD&T practice in India increasingly aligns with international ISO 2768 conventions, with IS 2102 as the local technical anchor.