Technical Drawings: Types, Standards, Uses & Best Practices

Technical drawings are one of the most critical tools for communication in engineering, manufacturing, architecture, construction, fabrication, or any field that involves product development. The drawings communicate information clearly to engineers, designers, manufacturers, contractors, fabricators, inspectors, and others who need instructions on how to interpret a design concept or create a particular product.

A good drawing goes well beyond conveying the shape of an object. The document communicates dimensions, materials, tolerances, finishes, symbols, notes, manufacturing instructions, assembly relationships, and any other details that might be needed to translate a design concept into a real-world product or structure.

Drawings can be developed manually or with computer-aided design (CAD) software. They can depict components, assemblies, buildings, piping systems, structural members, electrical elements, machine parts, or even a complete end-product. ISO 128-1:2020 contains general requirements related to the execution of technical drawings in 2D and 3D and applies to mechanical engineering, construction, architecture, or shipbuilding.

Even though 3D digital models are becoming more common, drawings still have an important role since they offer a controlled and easily understood way of communicating the design intent. A drawing can specify what needs to be manufactured, where a component goes, how things fit together, and which attributes are essential to function.

The quality of a drawing can directly impact the cost of manufacturing, time required for assembly, quality of the finished product, inspection results, and even deadlines for a project. A poorly executed or ambiguous dimension, tolerance, view, or note can result in rework that adds high cost.

This guide contains information related to technical drawings, including the purpose of drawings, types of drawings, components of a drawing, drawing standards, views and projections, dimensions, tolerances, symbols, CAD applications, revision practices, drawing applications, common errors, and best practices.

Table of Contents

1. What Are Technical Drawings?

2. Why Technical Drawings Are Important

3. Main Types of Technical Drawings

4. Parts of a Technical Drawing

5. Drawing Views and Projection Methods

6. Lines and Line Types

7. Dimensions and Dimensioning

8. Tolerances and Fits

9. Geometric Dimensioning and Tolerancing

10. Section Views

11. Detail and Auxiliary Views

12. Technical Drawing Symbols

13. Materials, Surface Finish, and Manufacturing Notes

14. Title Blocks and Drawing Information

15. CAD and Digital Technical Documentation

16. Drawing Standards and Codes

17. Creating a Technical Drawing: Step-by-Step Process

18. Technical Drawings in Manufacturing

19. Technical Drawings in Construction and Architecture

20. Technical Drawings in Mechanical Engineering

21. Technical Drawings in Fabrication and Assembly

22. Drawing Revision and Document Control

23. Common Technical Drawing Mistakes

24. Best Practices for Creating Better Drawings

25. Quality-Control Checklist

26. Future Trends in Technical Documentation

27. FAQs

28. Conclusion

29. Key Takeaway

What Are Technical Drawings?

A technical drawing is a standardized form of graphical communication used to convey information regarding a physical object, system, component, assembly, structure, or product.

Unlike an artistic rendering, a technical drawing is intended to communicate information accurately.

A technical drawing can convey:

• Shape

• Size

• Location

• Orientation

• Dimensions

• Tolerances

• Material

• Surface requirements

• Manufacturing processes

• Assembly relationships

• Inspection requirements

• Revision information

As a result, the drawing is part of the technical definition of a given product or project.

ISO 128-1:2020 contains a broad definition of the term technical drawing to cover documentation that specifies products, including workpieces, subassemblies and assemblies. The standard explicitly covers manual and computer-based drawings.

Drawing Versus Illustration

A technical drawing is not simply a picture or rendering of an object.

An illustration can convey appearance, but a technical drawing is a communication tool that can specify intent.

For example, an illustration of a shaft might depict the general form of the part, but a manufacturing drawing would need to include:

• Length

• Diameters

• Hole sizes and locations

• Thread specifications

• Chamfers

• Fillets

• Surface finish

• Material

• Dimensional tolerances

• Geometric tolerances where needed

Another example helps to illustrate the difference.

Manual and Computer-Based Drawings

Engineers and designers used to create drawings manually with pencils, pens, scales, drafting boards, templates, and other tools. Today, computer-aided design (CAD) dominates the design space. The fundamental principles are nonetheless the same:

• Clear representation

• Accurate geometry

• Standardized symbols

• Consistent dimensions

• Appropriate views

• Unambiguous requirements

Technology changes, but the need for good drawing fundamentals remains the same.

Why Technical Drawings Are Important

Engineering projects require communication.

It is possible for the designers to be in one building while the manufacturers are in another and the installation to occur in a third one. Engineering drawings enable communication and collaboration.

Communicating Design Intent

The main reason for creating a technical drawing is to communicate what the designer intends to manufacture or construct.

A drawing can answer questions such as:

• What is the shape of the required component?

• How big should it be?

• Where should holes be located?

• What material should be used?

• Which surfaces need to be machined or formed?

• How should components be put together?

• What dimensions are critical?

Supporting Manufacturing

Manufacturers need instructions for producing components.

A machinist, fabricator, or CNC programmer might need to refer to a drawing to determine:

• What stock material to use

• Dimensions for machining

• Locations for holes and other features

• Tolerances

• Threads

• Surface finish

• Inspection requirements

Supporting Inspection

Inspection teams need to know what to look for when evaluating a manufactured component.

By reviewing the drawing, an inspector can determine:

• Critical dimensions

• Tolerances

• Datums

• Surfaces that need to meet specific requirements

• Geometric controls

Reducing Ambiguity

Engineering drawings reduce ambiguity.

It is particularly important when several groups are working on a project together.

Preserving Engineering Information

Drawings can preserve engineering information for future generations.

If a project is started many years later or the first designer is no longer available, having controlled documentation allows the future engineer to understand the design intent.

Main Types of Technical Drawings

Various fields require specific types of drawings.

Detail Drawings

A detail drawing specifies a particular component.

The document generally contains all the information needed to manufacture or inspect the part. Common elements include:

• A variety of views

• Dimensions

• Tolerances

• Material

• Surface finish

• Notes

• Part number

• Revision

• Drawing scale

Assembly Drawings

An assembly drawing depicts how a product or system is put together.

It may include:

• Locations of components

• Item numbers

• Bill of materials

• Fasteners

• Section views

• Assembly notes

General Arrangement Drawings

General arrangement drawings show the overall layout of a system or installation.

These drawings are generally used in industrial, construction, structural, mechanical, or equipment industries.

Fabrication Drawings

Fabrication drawings contain information needed to manufacture a component or assembly.

Examples include steel, sheet-metal, weldment, and pipe spool drawings.

Installation Drawings

Installation drawings communicate how an item should be installed.

Drawings in this category may specify:

• Location

• Orientation

• Mounting

• Anchoring

• Clearances

• Connections

Exploded-View Drawings

Exploded views separate components to show how they fit together. This type of drawing is especially useful in creating:

• Assembly instructions

• Maintenance manuals

• Service documentation

• Product catalogs

Schematic Drawings

Schematics are diagrams that depict functional relationships, rather than views of actual objects.

Examples include electrical schematics, hydraulic, pneumatic, or control diagrams, process flow diagrams, and many others.

Piping and Instrumentation Drawings

Piping and instrumentation diagrams (P&ID) show equipment, piping, valves, instruments, and process relationships. P&ID drawings are different from fabrication drawings because the intent is to portray process relationships rather than specify every dimension for manufacturing.

Architectural Drawings

Architectural drawings communicate design intent for a building, structure, or installation. Common types of architectural drawings include:

• Floor plans

• Elevations

• Sections

• Site plans

• Reflected ceiling plans

• Detail drawings

Structural Drawings

Structural drawings contain design information for structural components such as beams, columns, braces, foundations, and connections.

Parts of a Technical Drawing

A typical professional-quality drawing contains several zones with specific information.

Drawing Area

The drawing area contains the graphical representation of a component or assembly.

It may include views, sections, details, dimensions, symbols, and notes.

Title Block

The title block typically contains general information about the drawing.

Elements generally included in the title block are:

• Drawing title

• Drawing number

• Revision

• Scale

• Sheet number

• Material

• Designer

• Checker

• Approver

• Date

• Company

• Projection method

Revision Block

The revision block contains a revision table that indicates changes made to the document.

Revisions generally include letters or numbers to identify the change, a description of the change, date, author, checker, approval, and so on.

Notes

Notes provide general instructions or requirements that apply to the drawing as a whole.

Examples of requirements that might be included in notes are:

• Tolerances

• Materials

• Surface treatment

• Welding

• Deburring

• Inspection

Bill of Materials

An assembly drawing may include a bill of materials that specifies components, including:

• Item number

• Part number

• Description

• Quantity

• Material

• Specification

Drawing Views and Projection Methods

One of the most fundamental aspects of drawing production involves selecting views that effectively communicate the object or assembly.

Front View

The front view typically conveys the aspect of an object that the designer wants to communicate first.

Top View

The top view can help show features that are not visible in the front view.

Side View

Side views help convey depth, width, holes, steps, profiles, and other features that are not visible in other views.

Isometric View

An isometric view provides a three-dimensional representation that is still reasonably technical.

This type of view is often used for assemblies, installations, or when the orientation of a component is critical to understanding.

Orthographic Projection

Orthographic drawings use multiple views to represent a 3D object in 2D form.

These drawings are particularly useful in manufacturing applications since each view contains measurable information.

First-Angle and Third-Angle Projection

Projection methods define how views are projected to create an accurate, easily interpretable representation.

A drawing should clearly indicate which method is being used through an appropriate set of symbols. Using the wrong projection method can lead to serious interpretation errors.

Choosing the Minimum Necessary Views

More views are not always better.

A drafter must choose views carefully to completely define the object or assembly. The goal is to use just enough views to fully define the component without creating excessive clutter.

Lines and Line Types

Lines play a critical role in engineering drawings.

ISO 128-2:2022 specifies types of lines, their designations and configurations, as well as rules regarding leader and reference lines in technical documents.

Visible Lines

Visible lines are used to convey outlines of objects that can be seen in a given view.

They are normally represented using prominent continuous lines.

Hidden Lines

Hidden lines are used to indicate features that cannot be seen directly.

Examples of features that might be conveyed using hidden lines include:

• Interior holes

• Recesses

• Hidden edges

Center Lines

Center lines indicate centers of rotation, symmetry, or other features.

Examples of features conveyed using center lines include:

• Axes

• Centers of holes

• Symmetry

• Rotational elements

Dimension Lines

Dimension lines are used to communicate dimensions.

They generally consist of:

• Extension lines

• Dimension text

• Arrows or other standardized line terminations

Section Lines

Section lines (also called hatching lines) indicate cut surfaces.

Leader Lines

Leader lines connect notes, symbols, or callouts to features in a drawing. Consistency is essential since users must be able to follow the lines and understand what they indicate. Errors in line usage or designation can result in serious misinterpretation of the drawing.

Dimensions and Dimensioning

Dimensions are among the most critical elements of a drawing.

A dimension communicates the expected size or location of a feature.

Linear Dimensions

A linear dimension can specify:

• Length

• Width

• Height

• Thickness

• Distance between features

Angular Dimensions

An angular dimension specifies the relationship between lines, surfaces, or features.

Diameter Dimensions

Diameter symbols are common for cylindrical features. For example:

Ø20

can indicate a nominal diameter of 20 units with an appropriate tolerance.

Radius Dimensions

Radius dimensions apply to arcs and rounded features.

Hole Callouts

Hole callouts can specify:

• Diameter

• Depth

• Quantity

• Counterbore

• Countersink

• Thread

• Hole type

Avoiding Duplicate Dimensions

A dimension should be indicated where it can be interpreted clearly without being unnecessarily repeated.

Repetition can create opportunities for error and confusion.

Dimension Placement

Dimensions should be arranged to:

• Maximize readability of text

• Avoid confusing extension lines

• Prevent dimension overlaps

• Facilitate finding critical dimensions

• Provide a clear presentation overall

Tolerances and Fits

No machined component is ever perfectly made to its nominal dimensions. Tolerancing defines acceptable variation.

Why Tolerances Matter

If a shaft is defined at 25 mm nominal diameter, its actual diameter might need to fall within a certain range. If no tolerance is defined, nobody knows what that range is.

General Tolerances

General tolerances reduce the need to specify tolerances on every dimension, though critical dimensions should still have explicit tolerancing.

Limits and Fits

Shaft and hole relationships define fits. Clearance, transition, and interference fits are categories of shaft-hole relationships.

A fit must be defined by the appropriate function.

Functional Tolerancing

Tolerancing decisions should be driven by function rather than precision. If a feature has no impact on overall assembly or performance, it probably does not need a critical tolerance.

Geometric Dimensioning and Tolerancing

Geometric Dimensioning and Tolerancing (GD&T) is a standardized way of defining acceptable geometric variation.

ASME Y14.5 is widely used as a standard for GD&T. The current ANSI listing identifies ASME Y14.5-2018 (R2024) "Dimensioning and Tolerancing" as specifying requirements for stating and interpreting dimensioning, tolerancing, and related requirements on engineering drawings and digital data.

Form Controls

Form controls relate to the shape of individual features. They include:

• Straightness

• Flatness

• Circularity

• Cylindricity

Orientation Controls

Orientation controls define the relationship between features. They include:

• Parallelism

• Perpendicularity

• Angularity

Location Controls

Location controls relate to the position of features. They include:

• Position

• Concentricity-related controls in applicable contexts

Profile Controls

Profile controls can define form and location of complex surfaces.

Runout Controls

Runout controls define allowable variation of a feature relative to a datum axis. Runout controls are useful on rotating features.

Datums

Datums define reference features or planes. A defined set of datums helps clearly communicate how the part should be located and measured.

Why GD&T Matters

GD&T improves communication by defining functional relationships rather than arbitrary plus-or-minus tolerances.

ASME notes that GD&T helps "communicate design intent related to form, fit, function, and interchangeability."

Section Views

Section views are useful for revealing internal geometry that would otherwise be defined by numerous hidden lines.

Full Section

A cutting plane passes completely through the object.

Half Section

One-half of the object is sectioned while the other half remains visible from the exterior. Half sections are useful for symmetrical objects.

Offset Section

An offset cutting plane can be helpful when multiple features of interest are not on the same plane.

Broken-Out Section

A broken-out section view reveals a specific interior feature.

Hatching

Hatching communicates the surfaces intersected by the cutting plane. Hatch lines should be spaced far enough apart to avoid interfering with dimensions or notes.

Detail and Auxiliary Views

Some objects simply cannot be adequately communicated using standard projections.

Detail Views

A detail view magnifies a small section of the object. Detail views are appropriate when:

• A feature is too small to be practical on the main view

• Several dimensions are crowded together

• A complex connection needs to be clarified

Auxiliary Views

Auxiliary views are useful for showing surfaces that are not parallel to the principal planes of projection.

An auxiliary view can be used to show the "true shape" of an inclined surface.

Enlarged Details

Features are sometimes too small to communicate effectively on the main view. An enlarged detail can avoid the need for excessive crowding of the main view.

Technical Drawing Symbols

Symbols can be used to communicate complex requirements compactly. Symbols appear in numerous technical drawing categories, including:

• Surface finish

• Welding

• GD&T

• Datum

• Diameter

• Radius

• Depth

• Countersink

• Counterbore

• Section

• Projection

Welding Symbols

Welding symbols can communicate:

• Type of weld

• Location of weld

• Size of weld

• Length of weld

• Contour of weld

• Finishing method for weld

Welding symbols must follow the conventions of the appropriate welding standard.

Surface Finish Symbols

Surface finish symbols can communicate requirements about the texture of a manufactured surface.

Thread Symbols

Thread callouts identify:

• Size

• Standard

• Pitch

• Class or tolerance where applicable

• Depth

• Internal/external designation

Datum Symbols

Datum symbols identify datums used for inspection and control.

Materials, Surface Finish, and Manufacturing Notes

Drawings sometimes need to communicate much more than geometry.

Material Specification

Material specification should be unambiguous. An appropriate specification might identify:

• Grade

• Standard

• Condition

• Heat treatment

• Mechanical requirements

Heat Treatment

Heat treatment can affect:

• Hardness

• Strength

• Toughness

• Wear resistance

If a particular condition is required, the drawing should clearly specify what that condition is.

Surface Treatment

Depending on the application, a surface might need:

• Plating

• Anodizing

• Painting

• Powder coating

• Passivation

• Heat treatment

• Surface hardening

Deburring

Machined or fabricated components often require burrs to be removed.

Special Processes

In some cases, special processes are integral to a component's function. When that is the case, the drawing or associated specification should identify the requirements.

Title Blocks and Drawing Information

Title blocks provide administrative information about a drawing.

Drawing Number

A unique drawing number is helpful for organizing the drawing set within an organization.

Revision

The revision should identify the current controlled version of the drawing.

Scale

Drawings have a scale, but dimensions on the drawing should govern, not visual measurements on the paper.

Approval Information

Many organizations use approval processes such as:

• Prepared by

• Checked by

• Approved by

Sheet Number

Multi-sheet drawing packages should be clearly organized.

Units

Drawing units should always be clearly identified since ambiguous units risk serious manufacturing errors.

CAD and Digital Technical Documentation

Computer-aided design has fundamentally changed engineering documentation by enabling parametric design and digital documentation.

Modern CAD solutions can support:

• Parametric modeling

• Assembly design

• Drawing generation

• Design revisions

• Bill-of-material extraction

• Interference checking

• Rendering

• Simulation integration

Parametric CAD

Parametric modeling uses the relationships between features and dimensions.

Drawing Generation

CAD solutions can generate views directly from 3D models.

While this can eliminate much tedious work, the generated drawing still requires engineering review.

Model-Based Definition

Modern engineering environments are increasingly using model-based definitions.

ASME Y14.5-2018 (R2024) notes that it applies to "dimensioning and tolerancing requirements for engineering drawings and digital data files, and related documents." Modern model-based engineering environments are moving toward a digital definition of a product.

CAD Does Not Guarantee Accuracy

CAD solutions that appear to automate many processes can still contain significant errors. Views can be missing, dimensions omitted, tolerances incorrect, model features miscalculated, standards misconfigured, and revisions poorly controlled. Human review is still critically important.

Drawing Standards and Codes

Standards define the language of engineering.

ISO 128

ISO 128 specifies general principles for the representation of technical drawings.

ISO 128-1:2020 specifies fundamental requirements and applies to both 2D and 3D technical drawings.

ISO 128-2:2022 specifies basic conventions of lines, including types, designations, configurations, and rules for leader and reference lines.

ASME Y14.5

ASME Y14.5 provides rules for dimensioning and geometric tolerancing.

The current ANSI listing identifies ASME Y14.5-2018 (R2024) and notes that it specifies "symbols, rules, definitions, requirements, defaults, and recommended practices for the dimensioning and tolerancing of engineering drawings."

ASME Y14.100

ASME Y14.100 covers engineering drawing practices. The ANSI Webstore describes the ASME Y14.5 and Y14.100 package as establishing "uniform practices for dimensioning, tolerancing, related requirements, and engineering drawing preparation and revision."

Choosing a Standard

Applicable standards will depend on:

• The location of the project

• Requirements from clients

• The industry

• Contract documents

• Manufacturing requirements

• Regulatory environment

Organizations should identify which standards apply to their drawings before production begins.

Creating a Technical Drawing: Step-by-Step Process

Organized engineers find that a step-by-step approach to creating drawings reduces errors and rework.

Step 1: Understand the Design

Before creating a drawing in a CAD solution, understand:

• What the part does

• How it fits with other parts

• What features are critical

• How it will be manufactured

• How it will be inspected

Step 2: Review the 3D Model or Design Data

Before starting the drawing, ensure that the 3D model or design data appears to be correct. Look at:

• Overall geometry

• Materials

• Features

• Interfaces

• Assembly relationships

Step 3: Select the Drawing Format

Choose an appropriate sheet size, orientation, scale, and template.

Step 4: Select Views

Select the minimum number of views needed to fully communicate the design.

Step 5: Add Dimensions

Add dimensions to functional features. Avoid adding dimensions that are ambiguous or unnecessarily repetitive.

Step 6: Add Tolerances

Apply general tolerances and specific tolerances where functional requirements demand.

Step 7: Add GD&T

Add GD&T where it helps communicate meaningful requirements about the function of a feature or relationship between features.

Step 8: Add Notes

Include any required notes about:

• Material

• Finish

• Heat treatment

• Deburring

• Welding

• Inspection

Step 9: Complete the Title Block

Ensure that:

• The drawing number is correct

• The revision is current

• The scale is correct

• The units are defined

• The author and checker are identified

• Approval information is complete

Step 10: Review

Perform a final review of the drawing. Imagine that you are:

• A machinist

• A fabricator

• An assembler

• An inspector

• A purchasing specialist

Ask yourself if each of these people has the information they need to accomplish their task without needing to guess.

Technical Drawings in Manufacturing

Production manufacturing relies heavily on drawings for production documentation. A production drawing can range from very general to extremely detailed, depending on what is needed for a particular process.

CNC Machining

Machinists may refer to drawings for:

• Stock size

• Finished size

• Hole locations and sizes

• Tooling

• Surface finishes

• Tolerances

Sheet-Metal Fabrication

Sheet-metal drawings can communicate:

• Thickness

• Bend locations

• Bend angles

• Hole patterns

• Formed features

• Welds

• Finishing requirements

Welding and Fabrication

Fabrication drawings might communicate:

• Member dimensions

• Material

• Weld requirements

• Joint configurations

• Inspection criteria

Quality Control

Inspectors use drawings as acceptance criteria. Drawings, specifications, and inspection criteria must be consistent.

Technical Drawings in Construction and Architecture

Construction projects rely on drawings for coordination between disciplines.

Architectural Drawings

Architectural documentation might define:

• Floor plans

• Elevations

• Sections

• Door/window schedules

• Finishes

• Details

Structural Drawings

Structural documents might define:

• Framing

• Foundations

• Columns

• Beams

• Reinforcement

• Connections

MEP Drawings

Documentation for mechanical, electrical, and plumbing systems can help ensure that all building systems work together.

Coordination

There might be thousands of requirements in a construction project. Clear documentation is essential to ensuring that:

• Architecture accommodates structure, mechanical, electrical, plumbing, and fire protection systems

• Structure accommodates architectural finishes and mechanical, electrical, plumbing, and fire protection systems

• Mechanical, electrical, plumbing, and fire protection systems accommodate each other

Technical Drawings in Mechanical Engineering

Mechanical Engineering involves a high degree of documentation of parts and assemblies.

Part Drawings

Individual part drawings define the geometry and production requirements of parts.

Assembly Drawings

Assemblies define how parts fit together.

Installation Drawings

Installation drawings explain how equipment should be installed.

Maintenance Drawings

Maintenance documentation can identify:

• Replacement parts

• Lubrication points

• Inspection points

• Adjustment points

Technical Drawings in Fabrication and Assembly

Fabrication shops need drawings that translate into actual products.

Cut Information

Fabrication drawings can communicate cut lengths.

Connection Details

Connections can define:

• Bolts

• Welds

• Plates

• Brackets

• Fasteners

Assembly Sequence

While some drawings do not show assembly sequences, they still provide valuable information about assembly.

Inspection Points

Critical dimensions and tolerances must be easy for inspectors to find.

Drawing Revision and Document Control

Designs change. Without proper document control, drawings can become obsolete.

Revision Identification

Each revision should have a unique identifier.

Revision Description

The revision description should briefly define what has changed.

Approval

Revisions should follow the organization's formal approval processes.

Superseded Drawings

Superseded drawings should be properly managed to ensure that obsolete documents are not mistaken for current documents.

Digital Document Management

Modern organizations use:

• Product lifecycle management systems

• Document management systems

• Cloud repositories

• Engineering change processes

To manage document control.

Common Technical Drawing Mistakes

Small errors in a technical drawing can lead to big problems later.

Incorrect Dimensions

A dimension error can lead to a nonfunctional part.

Missing Dimensions

Manufacturers may have to guess at missing information.

Conflicting Dimensions

Multiple dimensions for the same feature can confuse manufacturers.

Incorrect Projection

An incorrect view arrangement can cause a component to be incorrectly interpreted.

Crowded Drawing

Too many dimensions, notes, and views can make a drawing difficult to interpret.

Inconsistent Symbols

Symbols should be appropriate for and consistent with the applicable standard.

Missing Tolerances

A dimension without an appropriate tolerance may not convey the intended functional requirement.

Too Tight Tolerances

Tolerances that are too tight may unnecessarily increase manufacturing cost.

Poor Revision Control

Using an old drawing can result in manufacturing an obsolete design.

Not Accounting for Manufacturing

A drawing may specify a theoretically possible part that is impractical or expensive to manufacture.

Relying Only on a CAD Model

A 3D model does not always convey all the manufacturing and inspection requirements.

Best Practices for Creating Better Drawings

1. Start With the Manufacturing Process

Think about how the component will actually be made.

2. Focus on Functional Features

Clearly communicate dimensional and tolerance requirements for features that affect:

• Fit

• Function

• Interchangeability

• Safety

• Performance

3. Use Simple Views

Show enough views to define the object, but minimize the number of views used.

4. Follow Standards

Do not mix conventions unless there is a good reason.

5. Use Appropriate Tolerances

Tolerances should reflect functional requirements and manufacturing capability.

6. Use GD&T to Communicate Function, Not Complicate Drawings

GD&T should make it easier to understand how features of a part relate to each other, and it should not unnecessarily complicate a drawing.

7. Maintain Consistent Text and Line Weights

Consistent text and line weights make a drawing easier to read.

8. Avoid Ambiguous Notes

Notes should clearly and unambiguously specify requirements.

9. Check Interfaces

Make sure that mating components have compatible:

• Dimensions

• Hole patterns

• Datums

• Fits

• Clearances

10. Perform a Drawing Check

A second set of eyes can catch errors the drafter may have missed.

11. Think About the Inspector

A requirement must be measurable to be specified.

If a critical characteristic cannot be measured reliably, the specification of that feature may need to be revised.

12. Think About the Future

Documentation should be clear to future engineers who were not involved with the original design.

Quality-Control Checklist

Before final release, make sure that the following items have been checked on a drawing.

Geometry

• Are all required features shown?

• Are views correct?

• Are section views correct?

• Are features represented as hidden lines or otherwise?

Dimensions

• Are all manufacturing-critical dimensions present?

• Are dimensions easy to read?

• Are there conflicting or redundant dimensions?

• Are units indicated?

Tolerances

• Are general tolerances indicated?

• Are critical features indicated?

• Are fits appropriate?

• Is GD&T required?

Materials

• Is the material specified?

• Is the material grade correct?

• Are heat-treatment requirements indicated?

Manufacturing

• Can it actually be manufactured?

• Are special processes indicated?

• Are surface finishes specified?

Documentation

• Is the drawing number correct?

• Is the revision correct?

• Is the title block complete?

• Are approvals indicated?

Standards

• Are applicable standards indicated?

• Are symbols consistent with standards?

• Is the projection method indicated?

Assembly

• Do mating parts fit?

• Are clearances sufficient?

• Are fasteners accessible?

• Are interfaces defined?

Future Trends in Technical Documentation

Engineering documentation is changing as digital engineering becomes more sophisticated.

Model-Based Definition

Three-dimensional models increasingly contain information that would traditionally have been on a separate drawing.

This includes:

• Dimensions

• Tolerances

• Materials

• Manufacturing information

• Product metadata

Digital Manufacturing

Manufacturing systems are increasingly capable of consuming digital engineering information directly.

Automated Drawing Generation

CAD systems can automatically generate views, dimensions, and documentation.

Automated drawing generation can save time, but automated output should still be reviewed.

Artificial Intelligence

AI computer-aided engineering tools can identify:

• Missing dimensions

• Inconsistent tolerances

• Interference

• Violations of drawing standards

• Documentation errors

Digital Inspection

Inspection systems increasingly tie together CAD data and GD&T requirements with coordinate measuring machines and inspection reports.

Cloud Collaboration

Cloud-based engineering environments are making it easier for teams to collaborate on design documentation.

Document control and security are also important considerations.

FAQs

What are technical drawings used for?

Technical drawings communicate the geometry, dimensions, tolerances, materials, manufacturing requirements, assembly information, and any other information necessary to produce or construct a product, component, system, or structure.

What are the main types of technical drawings?

Common types of technical drawings include detail drawings, assembly drawings, fabrication drawings, installation drawings, general arrangement drawings, schematic drawings, architectural drawings, structural drawings, and specialized process documentation.

What is the difference between a technical drawing and a CAD model?

A CAD model primarily represents digital geometry and design information, whereas a drawing presents a controlled format for views, dimensions, tolerances, symbols, notes, and other requirements. Modern engineering increasingly employs both approaches.

What is GD&T?

Geometric Dimensioning and Tolerancing (GD&T) is a standardized method of specifying allowable geometric variation and relationships between features. ASME Y14.5 specifies widely used GD&T rules and symbols.

Why are drawing standards important?

Standards specify consistent rules and requirements for representation, dimensions, symbols, line types, tolerances, and documentation. This reduces ambiguity between designers, manufacturers, inspectors, and other stakeholders.

What is ISO 128?

ISO 128 is a series of international standards that address general principles of representation for technical product documentation. ISO 128-1:2020 specifies fundamental requirements and applies to both 2D and 3D technical drawings.

What does ISO 128-2 cover?

ISO 128-2:2022 specifies basic conventions for lines, designations, configurations, and other requirements for technical drawings.

Are technical drawings still necessary when a 3D CAD model exists?

Depending on the context, yes. A 3D model can contain a wealth of information, but organizations may still require drawings for manufacturing, inspection, contracts, approvals, installation, and controlled documentation. The appropriate approach depends on the project and applicable standards.

What software is used to create technical drawings?

Engineering CAD software packages can create drawings from 2D geometry or 3D models. The choice of software depends on the industry, company standards, project, and manufacturing or documentation requirements.

What makes a good technical drawing?

A good technical drawing is accurate, complete, readable, standardized, manufacturable, inspectable, and unambiguous. It contains only the information required to make or verify the intended result without requiring additional interpretation.

Conclusion

Well-prepared technical drawings continue to play a fundamental role in engineering and manufacturing because they translate design intent into a language that different engineering teams can understand.

A successful technical drawing goes beyond an attractive layout of views and dimensions. It is a controlled technical document that clearly describes what a component, assembly, system, or structure is supposed to be, and how its important characteristics are to be produced and verified.

The best technical drawings employ views, lines, dimensions, tolerances, symbols, materials, manufacturing notes, and revisions that appropriately support the design. ISO 128-1:2020 specifies general principles of representation for technical drawings across a range of engineering and construction disciplines, and ISO 128-2:2022 specifies conventions for lines and related representation.

Dimensioning and tolerancing are equally important considerations. ASME Y14.5-2018 (R2024) specifies a set of standardized symbols, rules, definitions, requirements, defaults, and recommended practices for communicating dimensioning and tolerancing requirements and supports the overall goal of communicating design intent for form, fit, function, and interchangeability.

Computer-aided design (CAD) has vastly improved the ability to create and share drawings, but technology does not replace engineering expertise. Designers and engineers continue to be responsible for understanding manufacturing processes, inspection, functional requirements, materials, tolerances, and applicable standards.

The best approach is to think critically about documentation from the beginning of the design process. Understand the function, identify critical features, select views, specify dimensions, and apply tolerances that make the final document interpretable by everyone who needs to use it.

When these best practices are employed, technical drawings can be much more than just documentation. They can accurately communicate design intent across engineering, manufacturing, inspection, assembly, construction, and the final product.

Key Takeaway

The best technical drawings effectively communicate design intent. Use standardized representation, carefully selected views, dimensioning of functional features, appropriate tolerances, revision control, and considerations for manufacturing and inspection to ensure that a finished drawing can be interpreted by anyone who needs to use it.

References

• ISO 128-1:2020 — Technical product documentation — General principles of representation — Part 1: Introduction and fundamental requirements. ISO states that the standard provides general rules for the execution of 2D and 3D technical drawings and applies to mechanical engineering, construction, architecture, shipbuilding, and manual and computer-based drawings.

• ISO 128-2:2022 — Technical product documentation — General principles of representation — Part 2: Basic conventions for lines. Includes line types, designations, configurations, leader lines, and reference-line conventions.

• ISO/TS 128-71:2010 — Simplified representation for mechanical engineering drawings. Contains principles and methods for simplified representation on mechanical engineering drawings.

• ASME Y14.5-2018 (R2024) — Dimensioning and Tolerancing. Specifies symbols, rules, definitions, requirements, defaults, and recommended practices for dimensioning and tolerancing, including use with engineering drawings and digital data.

• ASME Y14.100 — Engineering Drawing Practices. The ASME/ANSI package notes that Y14.100, when used in conjunction with Y14.5, establishes practices for the preparation, revision, dimensioning, tolerancing, and related requirements for engineering drawings.