General Tolerance Iso 2768-mk [ 90% DELUXE ]

Applies to flatness, straightness, perpendicularity, symmetry, and circular runout.

| Nominal Size Range (mm) | Flatness / Straightness (mm) | Perpendicularity (mm) | Symmetry (mm) | Circular Runout (mm) | | :--- | :--- | :--- | :--- | :--- | | 0.5 to 10 | 0.05 | 0.1 | 0.5 | 0.1 | | >10 to 30 | 0.1 | 0.2 | 0.5 | 0.1 | | >30 to 100 | 0.1 | 0.3 | 0.5 | 0.1 | | >100 to 300 | 0.2 | 0.4 | 0.5 | 0.1 | | >300 to 1000 | 0.3 | 0.5 | 0.5 | 0.1 | | >1000 to 3000 | 0.4 | 0.6 | 0.5 | 0.1 |

Important: For parallelism, the tolerance equals the value of the size tolerance. For positional tolerances, the standard recommends using ISO 2768-2 only for "non-functional" features; otherwise, individually specify.

The tolerance for angular dimensions depends on the length of the shorter side of the angle.

| Length of Shorter Side (mm) | Tolerance (± degrees/minutes) | | :--- | :--- | | Up to 10 | ± 1° | | Over 10 up to 50 | ± 0° 30' | | Over 50 up to 120 | ± 0° 20' | | Over 120 up to 400 | ± 0° 10' | | Over 400 | ± 0° 5' |

This report provides a comprehensive overview of the international standard ISO 2768-mK. This standard is utilized in mechanical engineering and manufacturing to simplify technical drawings. By applying general tolerances for linear and geometric dimensions, manufacturers can reduce drawing complexity while ensuring that parts remain functional and cost-effective.

The designation "mK" indicates a specific combination of tolerance classes:

In the title block or general notes section, write:

GENERAL TOLERANCES: ISO 2768-mk

This tells the machinist:

| Nominal Length Range | Tolerance (mm) | |----------------------|----------------| | ≤ 100 | 0.2 | | >100 – 300 | 0.3 | | >300 – 1000 | 0.4 | | >1000 – 3000 | 0.5 |

Duration: 90 minutes
Total marks: 100

Instructions:

Section A — Short answer and definitions (20 marks)

Section B — Table interpretation and application (20 marks) (Use the ISO 2768‑m and ISO 2768‑k tables below — simplified values given for the exam.)

Simplified linear tolerance table (mm):

Simplified angular tolerance:

Use these values for calculations.

Section C — Drawing interpretation and correction (20 marks) 10. (8) A drawing note reads “Tolerances: ISO 2768‑m”. The drawing also shows a critical hole Ø12 H7 (H7 tolerance explicitly shown). Explain which tolerance controls the hole and why. If the hole callout is Ø12 H7 with no additional notes, give the rationale whether ISO 2768 affects it. 11. (6) On an assembly drawing, a set of mating parts are dimensioned: shaft nominal Ø20 (no tolerance), mating bore nominal Ø20 (no tolerance); note reads ISO 2768‑mk. Is this acceptable for precision fit? Explain what the drawing should show to ensure a clearance fit of 0.02–0.05 mm. 12. (6) A supplier manufactured a part to k class tolerances though the drawing specified m class; the part’s critical dimension of 25 mm is out of tolerance for m but within k. Explain the likely consequences for assembly and recommended actions (3 points).

Section D — Problem solving & design considerations (40 marks) 13. (10) You are designing a bracket with multiple features. Explain, with brief justification, which features you would: a) apply ISO 2768‑m to (3 examples), b) require specific tighter tolerances (3 examples), and c) select ISO 2768‑k for (2 examples). 14. (8) Calculate cumulative tolerance stack-up for three aligned features in series: A, B, and C, nominal lengths 15 mm, 25 mm, and 40 mm respectively, all unspecified on the drawing and ISO 2768‑m applies. Use the simplified table above to compute worst‑case total length tolerance and resulting possible total length range. 15. (8) For the same features as Q14 but B is specified with a tighter machining tolerance of ±0.05 mm (explicit), while A and C remain under ISO 2768‑m, compute the worst‑case total length range. 16. (6) Explain how note “ISO 2768‑m unless otherwise specified” can reduce drawing clutter but also identify two risks associated with relying on general tolerances. 17. (8) A customer requires interchangeable parts with consistent function across suppliers. Propose a concise set of drawing practices (6 actionable items) to ensure interchangeability while using ISO 2768‑m where appropriate.

Extra credit (up to 5 marks)

Answer key (concise) — for examiner use only

Section A

Section B (using table) 6. Ø10 mm: a) m: ±0.15 → range 9.85–10.15 mm b) k: ±0.5 → range 9.5–10.5 mm 7. Length 45 mm: a) m: for 30–120 → ±0.2 → 44.8–45.2 mm b) k: for 30–120 → ±0.8 → 44.2–45.8 mm 8. Ø2.5 mm: a) m (≤3) ±0.1 → 2.4–2.6 mm b) k (≤3) ±0.3 → 2.2–2.8 mm 9. Angle 60°: m: ±1.0° → 59.0°–61.0° k: ±3.0° → 57.0°–63.0° If groove requires ±0.05 mm explicit tolerance, that explicit tolerance overrides ISO 2768 for that feature and ISO 2768 does not apply to that groove.

Section C 10. Ø12 H7 explicit callout controls; ISO 2768 does not override an explicit tolerance. H7 defines specific limits (hole basis tolerance); general tolerance ignored for that dimension. 11. Not acceptable for precision fit; drawing must specify tolerances (e.g., shaft Ø19.98–20.00 and bore Ø20.02–20.05) or use fit designation (e.g., H7/g6) to guarantee 0.02–0.05 mm clearance. 12. Consequences: possible assembly interference or functional failure; actions: reject/ rework part or negotiate acceptable nonconformance and update drawing tolerance notes; implement supplier corrective action.

Section D 13. Examples: a) Apply ISO 2768‑m to: nonfunctional external profile, noncritical hole pattern spacing, general bracket thickness. b) Tight tolerances for: mating surfaces/precision bores, shaft journal diameters, location/position of dowel holes. c) Apply ISO 2768‑k to: large noncritical cast features, rough-cut blanks. (Brief justification: cost vs function tradeoff.) 14. A±0.15, B±0.15, C±0.2 → worst‑case total tolerance = ±(0.15+0.15+0.2)=±0.5 mm. Nominal total = 80 mm → range 79.5–80.5 mm. 15. B ±0.05; total ±(0.15+0.05+0.2)=±0.4 mm → range 79.6–80.4 mm. 16. Benefits: reduces clutter, consistent defaults. Risks: designer assumptions hide critical tolerances; possible misinterpretation by manufacturers leading to nonconforming parts. 17. Six practices:

Extra credit

End of examination.

ISO 2768-mK standard is a combined specification used in technical drawings to define general tolerances for parts where specific tolerances are not individually noted. It streamlines the design process by providing a baseline for manufacturing accuracy without cluttering drawings with redundant data. Breakdown of the "mK" Designation

The designation combines two distinct parts of the ISO 2768 standard: 'm' (Medium): ISO 2768-1 . It governs general tolerances for linear and angular dimensions

, such as external sizes, internal sizes, radii, and chamfer heights. ISO 2768-2 . It governs geometrical tolerances

, specifically for features like straightness, flatness, perpendicularity, and symmetry. 1. ISO 2768-1: Linear & Angular Dimensions (Class 'm')

Class 'm' is the standard "medium" tolerance level typically used in CNC machining and general engineering. It defines the allowable deviation based on the size of the dimension: Nominal Size Range (mm) Tolerance (± mm) for Class 'm' > 30 to 120 > 120 to 400 > 400 to 1000 Angular Dimensions: general tolerance iso 2768-mk

Tolerances for angles also depend on the length of the shorter leg (e.g., ± 30' for lengths up to 10mm). Broken Edges:

Covers external radii and chamfer heights for deburred or rounded edges. 2. ISO 2768-2: Geometrical Tolerances (Class 'K')

Class 'K' provides general geometric limits for the form and orientation of features. It is divided into three classes: H (fine), K (medium), and L (coarse). Straightness and Flatness:

Limits are based on the length of the longest surface line or diameter. Perpendicularity: Controls the 90-degree relationship between surfaces.

Controls the alignment of features relative to a central axis.

General tolerances for circularity and total run-out are often handled by the same principles as the straightness/flatness of the related surfaces. KEYENCE CORPORATION OF AMERICA Application & Implementation Drawing Note:

To apply these standards, a designer simply adds a note like "General tolerances ISO 2768-mK" to the title block. Simplification:

This prevents "over-tolerancing," which can lead to unnecessarily high manufacturing costs by requiring tighter precision than the part's function demands. Exceptions:

If a specific feature requires higher precision than the general 'mK' level, the designer must explicitly label that individual dimension with its own tolerance. Summary of Benefits Cleaner Drawings: Reduces visual clutter by removing common tolerance ranges. Standardization:

Ensures that different machine shops interpret "standard accuracy" identically. Efficiency: Speeds up the CAD and inspection workflow.

For a detailed look at the specific tables for each class, you can refer to the official ISO 2768-1:1989 documentation technical summaries from manufacturers and the newer standard, which is intended to eventually replace it?

The Basics of General Tolerance Standard – ISO 2768-mK - Eurotools

ISO 2768-1 stands for the general tolerances for linear and angular dimensions without individual tolerance indications, ISO 2768-

What is ISO 2768? | CNC Machining Tolerance Standards - Fictiv

ISO 2768-mK standard defines general tolerances for dimensions and geometric features on technical drawings where specific tolerances are not indicated. It simplifies drawings by providing a default "medium" level of precision, ensuring parts fit together without over-specifying every dimension. Meaning of "mK" "m" (Medium) : Refers to ISO 2768-1 , covering general tolerances for linear and angular dimensions (lengths, diameters, radii, chamfers). "K" (Medium) : Refers to ISO 2768-2 , covering general geometrical tolerances

(straightness, flatness, perpendicularity, symmetry, and circular run-out). Tolerance Tables for ISO 2768-mK All values are in millimeters (mm) unless otherwise stated. ALFA MIMtech 1. Linear Dimensions (Class m) Applies to external sizes, internal sizes, and diameters. Range (Nominal Size) Tolerance (±) 0.5 to 3 mm >3 to 6 mm >6 to 30 mm >30 to 120 mm >120 to 400 mm >400 to 1000 mm >1000 to 2000 mm >2000 to 4000 mm 2. External Radii and Chamfer Heights (Class m) Applies to broken edges and rounded corners. ALFA MIMtech Range (Nominal Size) Tolerance (±) 0.5 to 3 mm >3 to 6 mm 3. Angular Dimensions (Class m) Applies to angular measurements. ALFA MIMtech Length of Short Side Tolerance (±) Up to 10 mm >10 to 50 mm >50 to 120 mm >120 to 400 mm Over 400 mm 4. Geometrical Tolerances (Class K) Applies to the form and position of features. waterson.com Feature Type Range (Nominal Length) Straightness & Flatness Up to 10 / 30 / 100 / 300 / 1000 / 3000 mm 0.05 / 0.1 / 0.2 / 0.4 / 0.6 / 0.8 mm Perpendicularity Up to 100 / 300 / 1000 / 3000 mm 0.4 / 0.6 / 0.8 / 1.0 mm Up to 100 / 300 / 1000 / 3000 mm 0.6 / 0.6 / 0.8 / 1.0 mm Circular Run-out All lengths Important Considerations Understanding ISO 2768-mK Tolerances for Engineers Important: For parallelism , the tolerance equals the

ISO 2768-mK is an international standard for general tolerances used to simplify technical drawings by providing default limits for dimensions and geometric features that do not have specific tolerance markers. 🛠️ What "mK" Means

The designation combines two different parts of the standard:

m (Part 1): Represents the Medium tolerance class for linear and angular dimensions (lengths, radii, angles).

K (Part 2): Represents the K tolerance class for geometrical features (flatness, straightness, perpendicularity, symmetry). ISO 2768-1: Linear Dimensions (Class m)

These tolerances apply to dimensions like length, width, and diameter when not specified. All values below are in mm. Nominal Range (mm) Tolerance (±) 120 to 400 400 to 1000 1000 to 2000 2000 to 4000 Additional "m" class values:

External Radii & Chamfers: ±0.2 mm (for 0.5–3mm) to ±1.0 mm (over 30mm).

Angular Dimensions: ±1° (up to 10mm length) to ±0°10' (over 400mm). ISO 2768-2: Geometrical Tolerances (Class K)

This part controls the shape and position of features to ensure they fit correctly. Feature Type Tolerance Rule for Class K Straightness / Flatness

Ranges from 0.05 mm (up to 10mm length) to 0.6 mm (over 1000mm). Perpendicularity Max 0.6 mm for lengths up to 300mm. Symmetry Max 0.6 mm up to 300mm length. Run-out 0.2 mm (standard for class K). 🎯 When to Use ISO 2768-mK Understanding ISO 2768-mK Tolerances for Engineers

A feature for ISO 2768-mk establishes a "medium" precision standard for parts, ensuring they are manufactured within acceptable limits for both size and shape without requiring individual tolerance callouts for every dimension. The designation breaks down into two parts:

m (Medium): Governed by ISO 2768-1, this defines permissible deviations for linear and angular dimensions, such as lengths, radii, and chamfers.

k (Class K): Governed by ISO 2768-2, this covers geometric characteristics like flatness, straightness, and circular runout. Tolerance Tables for ISO 2768-mk

The following values apply based on the nominal size of the feature: Linear Dimensions (Class m)

For linear measurements like external/internal sizes, heights, and distances. Nominal Range (mm) Tolerance (± mm) 120 to 400 400 to 1000 Geometric Tolerances (Class K)

For shape and position characteristics without individual indications. Feature Type Range (mm) Tolerance (mm) Straightness/Flatness 100 to 300 Perpendicularity Symmetry Run-out (Circular) All ranges Key Implementation Details

The Basics Of General Tolerance Standard - ISO 2768-mK - LEADRP The tolerance for angular dimensions depends on the

| Nominal Size Range (mm) | Tolerance (± mm) | | :--- | :--- | | 0.5 up to 3 | ± 0.1 | | Over 3 up to 6 | ± 0.1 | | Over 6 up to 30 | ± 0.2 | | Over 30 up to 120 | ± 0.3 | | Over 120 up to 400 | ± 0.5 | | Over 400 up to 1000 | ± 0.8 | | Over 1000 up to 2000 | ± 1.2 | | Over 2000 up to 4000 | ± 2.0 |

Note: For dimensions below 0.5 mm, the tolerance shall be stated explicitly on the drawing.