ISO 2768: Стандартныя допускі для дакладнай вытворчасці

In the ever-evolving field of precision manufacturing, achieving consistent quality and ensuring efficiency is paramount.

Tolerances—the allowable variation in a dimension—play a crucial role in maintaining the integrity of manufactured parts.

ISO 2768 is an international standard designed to simplify and streamline the specification of tolerances in technical drawings.

This blog explores ISO 2768 in detail, explaining its classifications, прыкладанне, and benefits in modern manufacturing.

Whether you’re a designer, engineer, or manufacturer, understanding ISO 2768 can significantly enhance your processes and outcomes.

2. What is ISO 2768?

It is an international standard that establishes general tolerances for linear, кутняй, and geometrical dimensions in technical drawings.

It eliminates the need to individually specify tolerances for every feature, simplifying the design process.

Primarily, ISO 2768 applies to parts made through machining, ліццё, і выраб ліставога металу.

Напрыклад, when a technical drawing specifies a dimension of 50 mm but does not indicate a tolerance,

ISO 2768 provides default tolerances based on the tolerance class (e.g., Fine or Medium).

This approach reduces ambiguity and ensures clarity in communication between designers and manufacturers, even across different countries and industries.

3. Key Classifications in ISO 2768

ISO 2768 is divided into two main categories that address different aspects of tolerances: general tolerances і geometrical tolerances.

Each category includes specific classifications to ensure clarity and precision in manufacturing and design.

General Tolerances

General tolerances in ISO 2768 apply to linear and angular dimensions that do not have individual tolerance specifications on the drawing.

They ensure that designers can avoid overloading drawings with unnecessary details while maintaining accuracy.

• Лінейныя памеры:
  Covers measurements like length, width, вышыня, і таўшчыня. Напрыклад, a dimension of 50 mm with a medium tolerance class (м) might allow a deviation of ±0.2 mm.
• Вуглавыя памеры:
  Addresses angular features such as chamfers, slopes, and inclinations.
  Tolerances here depend on the angle size and the selected tolerance class, ensuring alignment without excess precision.

Geometrical Tolerances

This category covers the form and positional accuracy of features.

Geometrical tolerances help maintain functionality, especially in assemblies where misalignments could lead to performance issues.

Key elements include:

• Пляскатасць: Ensures that a surface is even within specified limits.
• Прамалінейнасць: Controls how much a line or edge can deviate from a straight path.
• Перпендыкулярнасць: Maintains the right-angle relationship between two features.
• Сіметрыя: Guarantees balanced and uniform features around a central axis.

Tolerance Classes

ISO 2768 introduces four tolerance classes to match the precision level to the application’s needs. These classes are:

• Fine (f): For applications requiring high precision, such as aerospace or medical devices.
• Сярэдні (м): The most commonly used class, падыходзіць для прымянення агульнага прызначэння.
• Coarse (в): Ideal for less critical dimensions or larger parts.
• Very Coarse (в): Used for parts with minimal complexity or large-scale components.

4. ISO 2768 Part 1: Linear and Angular Dimensions

ISO 2768 Part 1, titled “Unspecified Tolerances for Linear and Angular Dimensions,” is a critical component of the ISO 2768 standard suite.

It provides default tolerances for linear and angular dimensions that are not explicitly specified on technical drawings.

This part of the standard aims to simplify design documentation by reducing the need to specify individual tolerances for every dimension,

thereby streamlining the manufacturing process while ensuring that parts meet acceptable quality standards.

Scope and Application

ISO 2768 Part 1 applies to linear and angular dimensions in technical drawings where no specific tolerance is indicated.

It is intended for use in situations where general machining practices can achieve the necessary precision. The standard covers:

• Linear dimensions: Includes external and internal sizes, дыяметры, distances, chamfer heights, and radii.
• Angular dimensions: Covers angular measurements where specific tolerances are not indicated.
• Dimensions of machined and assembled parts: Applicable to both linear and angular dimensions produced during the machining of assembled components.

Tolerances for Linear Dimensions

The table below outlines the ISO 2768 tolerance limits for linear dimensions across different nominal size ranges：

LINEAR DIMENSIONS
Permissible deviations in mm for ranges in nominal lengths	Tolerance class designation (description)
	f (цудоўны)	м (сярэдні)	в (coarse)	в (very coarse)
0.5 да 3	±0.05	±0,1	±0.2	-
над 3 да 6	±0.05	±0,1	±0.3	±0.5
над 6 да 30	±0,1	±0.2	±0.5	±1.0
над 30 да 120	±0.15	±0.3	±0.8	±1.5
над 120 да 400	±0.2	±0.5	±1.2	±2.5
над 400 да 1000	±0.3	±0.8	±2.0	±4.0
над 1000 да 2000	±0.5	±1.2	±3.0	±6.0
над 2000 да 4000	-	±2.0	±4.0	±8.0

How to read the table: For a part with a nominal dimension range of 50 мм, under the Fine (f) tolerance class, the acceptable deviation would be ±0.15 mm.

Tolerances for External Radius and Chamfer Heights

The table below shows the ISO 2768 standard tolerances for external radii and chamfer heights.
These tolerances define permissible deviations for curved surfaces and chamfered edges.

EXTERNAL RADIUS AND CHAMFER HEIGHTS
Permissible deviations in mm for ranges in nominal lengths	Tolerance class designation (description)
	f (цудоўны)	м (сярэдні)	в (coarse)	в (very coarse)
0.5 да 3	±0.2	±0.2	±0.4	±0.4
над 3 да 6	±0.5	±0.5	±1.0	±1.0
над 6	±0,1	±1.0	±2.0	±2.0

How to read the table: For an external radius of 4 мм, the applicable nominal dimension range is ‘over 3 да 6 mm.’

If you select the Fine (f) tolerance class, the acceptable deviation would be ±0.5 mm.

Tolerances for Angular Dimensions

The table below details the ISO 2768 tolerances for angular dimensions, expressed in degrees and minutes. These tolerances apply to the shorter leg of an angle.

ANGULAR DIMENSIONS
Permissible deviations in mm for ranges in nominal lengths	Tolerance class designation (description)
	f (цудоўны)	м (сярэдні)	в (coarse)	в (very coarse)
да 10	±1°	±1°	±1°30′	±3°
над 10 да 50	±0°30′	±0°30′	±1°	±2°
над 50 да 120	±0°20′	±0°20′	±0°30′	±1°
над 120 да 400	±0°10′	±0°10′	±0°15′	±0°30′
над 400	±0°5′	±0°5′	±0°10′	±0°20′

How to read the table: For an angular measurement with a nominal dimension range of 30 мм, under the Fine (f) tolerance class, the acceptable deviation would be ±0°30′.

5. ISO 2768 Part 2: Geometrical Tolerances for Features

ISO 2768 Т2 refers to the part of ISO 2768 that governs geometrical tolerances, focusing specifically on form, арыентацыя, location, and runout tolerances for features.

These tolerances are critical for ensuring proper functionality, assembly precision, and overall quality of manufactured components.

Scope and Application

ISO 2768 T2 applies to:

• Geometrical tolerances that are not explicitly mentioned on technical drawings.
• Components where precision in geometry is crucial for assembly or operation.
• General-purpose manufacturing, with predefined tolerance levels to balance quality and cost.

Geometrical Tolerances Defined in T2

ISO 2768 T2 specifies tolerances for the following features:

1. Form Tolerances:

• • Пляскатасць: Ensures a surface lies within a defined plane.
  • Прамалінейнасць: Controls the straightness of an edge or axis.
  • Roundness: Maintains circular consistency.
  • Cylindricity: Ensures cylindrical surfaces remain consistent.

2. Orientation Tolerances:

• • Паралелізм: Maintains parallel relationships between surfaces or axes.
  • Перпендыкулярнасць: Ensures surfaces or features are at 90° angles.
  • Angularity: Specifies a precise angle between surfaces.

3. Location Tolerances:

• • Position: Defines the allowable deviation from the intended position.
  • Канцэнтрычнасць: Ensures the center of one feature aligns with another.
  • Сіметрыя: Controls symmetry for balanced designs.

4. Runout Tolerances:

• • Circular Runout: Limits the deviation of a feature during rotation.
  • Total Runout: Controls the overall deviation of a surface in motion.

6. The Importance of ISO 2768 in Manufacturing

ISO 2768 provides multiple advantages for manufacturers:

• Стандартызацыя: Ensures parts from different suppliers meet consistent quality standards.
• Clear Communication: Reduces misinterpretation in technical drawings, minimizing errors.
• Global Compatibility: Facilitates collaboration across international supply chains.

Напрыклад, a multinational company can use ISO 2768 to ensure that parts sourced from different regions fit together seamlessly, reducing delays and rework.

7. How ISO 2768 Works

ISO 2768 provides a standardized approach to tolerances in manufacturing, Спрошчаны дызайн, communication, and production processes.

It works by defining general tolerances for dimensions and geometrical features when specific tolerances are not explicitly stated on technical drawings.

Here’s a detailed explanation of how ISO 2768 функцыі:

Step-by-Step Explanation

1. Incorporation into Design

• General Tolerances: Instead of specifying tolerances for every dimension, engineers use ISO 2768 to apply default tolerances.
  Напрыклад, a shaft length listed as 100 mm would automatically include a tolerance range defined by ISO 2768, such as ±0.2 mm for medium (м) class.
• Geometrical Tolerances: Features like flatness or perpendicularity are governed by ISO 2768 Part 2, ensuring consistency in form and alignment.

2. Communication in Technical Drawings

• The technical drawing includes a note like “ISO 2768-mK,” where:

• • м indicates the medium tolerance class for linear and angular dimensions (Part 1).
  • К refers to the geometrical tolerances for features (Part 2).

• This shorthand eliminates the need to detail tolerances for each dimension individually, saving time and reducing errors.

3. Application in Manufacturing

• During production, manufacturers follow the ISO 2768 tolerance class specified on the drawings.
• Tolerance guidelines ensure that deviations within the limits do not impact part functionality or fit.
• Consistency is maintained across batches, even with different suppliers.

4. Інспекцыя і кантроль якасці

• Measurement Tools: Inspection teams use calipers, мікраметры, and CMM machines to verify that dimensions and geometrical features meet ISO 2768 tolerances.
• Tolerance Stacking: Evaluates how dimensional deviations might accumulate and affect assembly. Proper application of ISO 2768 minimizes issues caused by excessive stacking.

Прыклад:

A drawing specifies a hole diameter of 20 mm under ISO 2768-f. For a fine tolerance class, the permissible deviation might be ±0.1 mm.

During inspection, a measured diameter of 20.08 mm would conform to the standard, але 20.12 mm would not.

Advantages of How ISO 2768 Функцыі

1. Clarity in Communication

• • Reduces ambiguity by providing a clear, universal guideline for tolerances.
  • Promotes better collaboration between designers, вытворцаў, and suppliers.

2. Efficiency in Production

• • Streamlines the manufacturing process by eliminating the need for detailed tolerance specifications.
  • Encourages the use of cost-effective and consistent practices.

3. Забяспечанасць якасцю

• • Ensures parts meet design intent without requiring overly tight tolerances, which can increase costs unnecessarily.
  • Facilitates robust quality control processes with well-defined standards.

Common Missteps and How to Avoid Them

1. Ignoring ISO 2768 Заняткі: Ensure the appropriate tolerance class (цудоўны, сярэдні, coarse, very coarse) is selected based on the application’s precision requirements.
2. Over-Specification: Avoid assigning tighter tolerances than necessary, as this can increase manufacturing costs.
3. Tolerance Stacking Mismanagement: Be mindful of accumulated tolerances when designing assemblies to prevent misalignment or fitment issues.

8. How to Choose the Right Tolerance

Choosing the correct tolerance is vital to achieving a balance between functionality, падыходзяць, каштаваць, і вытворчасць.

Tolerances that are too tight can increase manufacturing complexity and costs, while overly loose tolerances may compromise part performance and assembly.

The goal is to select a tolerance level that ensures proper part functionality without unnecessary expense.

Key Considerations in Tolerance Selection

1. Функцыянальнасць

• • Determine the operational requirements of the part, such as load-bearing capacity, рух, or sealing performance.
  • Identify whether the part must align with other components and the precision required for proper assembly.

2. Вытворчы працэс

• • Understand the capabilities of the chosen manufacturing process. Напрыклад:

• • • CNC machining generally supports tighter tolerances than 3D printing.
    • Sheet metal fabrication may have limitations for fine tolerances.

3. Выбар матэрыялу

• • Пэўныя матэрыялы, like plastics, may require looser tolerances due to thermal expansion or flexibility, while metals can typically hold tighter tolerances.

4. Кошт супраць. Дакладнасць

• • Tight tolerances usually increase production costs due to additional machining time and quality control.
  • Opt for looser tolerances when high precision isn’t critical.

5. Стандарты

• • Refer to standardized tolerance classes such as ISO 2768 альбо ISO 286 to ensure consistency and compatibility in global manufacturing.

Guidance for Selecting Tolerance Standards

Прымяненне	Апісанне	Recommended tolerance standard	Reason for tolerance choice
Precision machined parts	High-precision components are used in aerospace, аўтамабільны, or medical devices where exact fit is critical.	ISO 2768 Fine and ISO 286 Сартаваць 6 (IT6) або вышэй	Ensures minimal variation for linear and angular dimensions (ISO 2768) and tight control for cylindrical fits (ISO 286).
Interchangeable mechanical parts	Parts are designed to be easily replaced or exchanged, like gears, арыентыроўка, and fasteners in assemblies.	ISO 2768 Fine and ISO 286 Сартаваць 7 (IT7) або вышэй	Allows for precise linear/angular fits (ISO 2768) and standardized fits for shafts and holes (ISO 286).
General mechanical assemblies	Components in general machinery that require good fits but not ultra-high precision, like housings or brackets.	ISO 2768 Сярэдні	Provides a balance between precision and manufacturability for linear and angular dimensions.
Large fabricated structures	Parts used in construction or heavy machinery where exact fits are less critical, such as beams or plates.	ISO 2768 Сярэдні	Tolerances accommodate larger dimensions and processes like welding or fabrication.
Plastic components	Molded or machined plastic parts for consumer products or electronics, where some dimensional variability is acceptable.	ISO 2768 Medium and ISO 286 Сартаваць 8 (IT8) або вышэй	Tolerances consider material flexibility (ISO 2768) and accommodate standard fits (ISO 286) for plastics.
Shafts and holes for rotating components	Components like shafts and holes in rotating machinery require specific fits to ensure proper function.	ISO 2768 Fine and ISO 286 Гатункі 6 або 7 (IT6, IT7)	Ensures precise linear/angular dimensions (ISO 2768) and tight fits for rotational balance (ISO 286).
Sheet metal parts	Parts made from sheet metal for enclosures, панэлі, and brackets where tight fits are not critical.	ISO 2768 Сярэдні	Tolerances are suitable for processes like bending and forming, accommodating inherent variabilities.
Electrical enclosures and casings	Enclosures for electrical components that must fit together but do not require tight tolerances.	ISO 2768 Сярэдні	Provides sufficient accuracy for assembly while reducing costs for non-precision parts.
Consumer product components	Parts in consumer electronics or appliances where aesthetic finish and function are prioritized over tight tolerances.	ISO 2768 Medium and ISO 286 Сартаваць 8 (IT8)	Balances manufacturing efficiency with adequate fit and function, using standard tolerances for general fits.

9. ISO vs. ASME Tolerance Standards

ISO and ASME standards serve as critical frameworks for defining tolerances, ensuring consistency, and facilitating efficient global manufacturing practices.

While both aim to achieve precision and clarity in engineering drawings, their application and regional prevalence differ significantly.

• Стандарты ISO: Primarily used in Europe, the UK, Turkey, and parts of Asia, focusing on general tolerances (e.g., ISO 2768) and specific fit systems (e.g., ISO 286).
  These standards simplify dimensional tolerances and ensure uniformity across industries.
• Стандарты ASME: Dominant in the United States, these standards (e.g., ASME Y14.5 and ASME B4.1) emphasize geometric dimensioning and tolerancing (Gd&T)
  with detailed guidelines for defining form, арыентацыя, and positional tolerances.

Comparison of ISO and ASME Tolerance Standards

Стандарт ISO	Equivalent ASME Standard	Прымяненне	Key Difference
ISO 2768 for Angular Dimensions	ASME B4.2	Angular dimension tolerances	Similar angular tolerance ranges, but ASME B4.2 may offer more detailed instructions for specific applications.
ISO 1101 (Geometric Tolerancing)	ASME Y14.5 (Gd&T)	Geometric tolerancing of shapes and features	Both provide frameworks for GD&T, but ASME Y14.5 is more detailed and widely used in the US.
ISO 286 (Сартаваць 6, 7, 8)	ASME B4.1 (Сартаваць 6, 7, 8)	Tolerances for cylindrical fits and distances between parallel surfaces	Both standards define similar tolerance grades for fits, but ASME includes additional guidance specific to US practices.
ISO 2768 (Fine, Сярэдні)	ASME Y14.5	General tolerances for linear and angular dimensions	ISO 2768 provides general tolerances, while ASME Y14.5 offers detailed geometric dimensioning guidelines (Gd&T).

Example of Equivalency

• General Dimensional Tolerances:

• • ISO 2768-m aligns with ASME B4.1 for medium precision.

• Geometric Tolerances:

• • ISO 1101 covers similar principles as ASME Y14.5, but ASME provides more detailed guidelines for complex assemblies.

10. Conclusion

ISO 2768 is a foundational tool for precision manufacturing, simplifying the specification of tolerances and enhancing efficiency.

By promoting standardization and clarity, it reduces costs, minimizes errors, and ensures high-quality results.

Adopting ISO 2768 in your design and manufacturing processes can lead to smoother operations, better collaboration, and superior products.

If you’re looking for professional manufacturing services that comply with ISO 2768, contact our experts today and take your projects to the next level.