Delineation

Line Conventions and Lettering

This section establishes the line and lettering practices for use in preparing engineering drawings. It recognizes the requirements for both CAD (Computer Aided Design) and manual preparation. The use of the specified line widths and letter heights will meet reproduction and microfilm requirements.

American Society of Mechanical Engineers (ASME), Line Conventions and Lettering, Y14.2M has been approved as an American national standard by the American National Standards Institute (ANSI). The standard was completely metricated (with inch equivalents for letter heights) in recognition of the European Economic Community Initiative and the government directive that specifies that all new research and development contracts should specify the metric system of measurement. The complexity of letter heights was reduced from ten to three for both metric and inch drawings.

The following describes the size, construction and application of line types used in the production of engineering drawings. These lines should be uniform, sharp, and opaque.

Multi- and Sectional-View Drawings

This section is in accordance with ASME Y14.3M- 1994. It establishes the requirements for Multiview and Sectional view drawings. The topics covered are:

  1. Third angle projection
  2. First angle projection
  3. Standard arrangement of six principal views
  4. Projection symbols
  5. Views
  6. Detail views
  7. Section views
  8. Drafting Conventions

Reference Documents

    American National Standards Institute (ANSI)
    American Society of Mechanical Engineers (ASME)
    ANSI Y14.1 Drawing Sheet Size and Format
    ASME Y14.1M Metric Drawing Sheet Size and Format
    ASME Y14.2M Line Conventions and Lettering

Pictorial Drawing

Pictorial drawing is the oldest graphics form of recorded communication known to man and has evolved over the years to its current form. This standard addresses those kinds of pictorials most commonly used on engineering drawings.

Pictorial drawings may be prepared to completely replace or avoid preparation of conventional drawings. This may be done where the complexity of the objects is intimidating and difficult to describe in conventional orthographic form. Pictorial drawings are useful in design, construction or production, erection or assembly, service or repair, and sales. They are used to explain complicated engineering designs to those who have difficulty understanding conventional multiview drawings; they may assist the designer in working out spatial problems such as clearances and interferences; they can enhance the assembling of a product or facilitate the ordering of new parts; they may convey ideas from one person to another, from shop to shop, or from salesperson to purchaser. They may also be used to develop the power of visualization. The kind of pictorial drawing made will depend on the purpose for which it is drawn and the kind of talent involved.

Types/Applications of Eng'g Drawings

This section is in accordance with ASME Y14.24-1999. It establishes the requirements for Types and Applications of Engineering drawings. Each drawing type describes the application and the minimum content requirements. Other industries such as marine, civil, construction and optics are not part of ASME Y14.24.

Reference Documents

    American National Standards Institute (ANSI)
    American Society of Mechanical Engineers (ASME)
    Institute of Electrical and Electronic Engineers (IEEE)
    Institute for Interconnecting and Packaging Electronic Circuits (IPC)
    ANSI/IEEE - Graphic Symbols for Logic Functions
    ANSI/IEEE 200 - Reference Designations for Electrical and Electronic Parts and Equipment
    ANSI/IEEE 991 - Logic circuit Diagrams
    IEEE - 315 - Graphic Symbols for Electrical and Electronic Equipment
    ANSI/IPC-D-249 - Design Standard for Flexible 1 & 2 Sided Printed Wiring Boards
    ANSI/IPC-D-275 - Design Standard for Rigid Printed Board and Rigid Printed Board Assemblies
    ANSI/IPC-D-310 - Guidelines for Artwork Generation and Measurement Techniques
    ANSI/IPC-D-325 - End Product Documentation for Printed Boards
    ANSI/IPC -DW-425 - Design and End Product Requirements for Discrete Wiring Boards
    ANSI/IPC-D-859 - Design Standard for Thick Film Multilayer Hybrid Circuit
    ASME Y14.34M - Associated List
    Federal Cataloging Handbook H4/H8 - Commercial and Government Entity Codes

Simplified (Functional) Drafting

Functional/simplified drafting is a technique where drawings are developed with the functional use being the primary driver. Today, more than ever before, the challenge of industry is to produce more and better goods with less effort. The quest is to keep prices competitive so that the company can not only maintain but continue to gain additional market share and profit. This means that the drawing information must be clear and concise, without artistic rendering, unnecessary details, and superfluous (redundant, excessive, needless, extravagant) information. Unnecessary data on drawings adds to the cost of design development, detracts from a design and potentially adds complexity to the interpretation, revision and record retention of the drawing.

The application of functional/simplified drawing is as important today as when it was initially introduced in the late 1950s. Functional/simplified drafting was introduced to increase drawing production without losing the fit, form, or function of the depicted design. The idea is to reduce unnecessary information that does not reduce the user's ability to interpret the drawing. High quality drawings are needed by users to perform their work, e.g., procurement, fabrication, and quality inspection.

Conventional Representations

This section of the manual has been reduced in size over time because of industry standards development that covers nearly every aspect of graphical representation for each discipline. The result is high quality standards that allow improved readability for drawing users. All the sections of this manual are developed or revised using the latest nationally accepted standards.

Conventional representations detailed in this section cover items not found elsewhere in the manual, and where general industry practice is still recognized as not being replaced by a national consensus standard. Consideration is given to both CAD and manual drawings. The principles are sound and produce drawings that are functional. The practice also applies to both new and revised drawings.

Drawing Preparation for Microfilming

With the increase of computer generated documents, specifically engineering drawings, parts lists and specifications, requirements for microfilming preparation must be given considerable attention. Both manually and computer-generated documents should be prepared for eventual microfilming, even though in the case of computer-generated drawings, the "MASTER" is resident on a disk or a magnetic tape in the form of digital data. Simplicity and clarity of documentation are the prime factors contributing to quality microfilm/microfiche and reproduction.

Whether the documentation is manually or computer-generated, the use of quality media, attention to proper care and handling of originals are very important factors. The function that is responsible for engineering documentation must exercise continuous control over these important aspects of drawing preparation to assure quality of microfilm and reproduction.

Descriptive Geometry

Descriptive Geometry is a graphic method for finding the solution to a problem and a means for presenting geometric relationships. For many engineering problems, a graphic solution can serve as a rough check for an analytical solution. In drafting, the graphic solution is the primary means by which descriptive geometry problems are solved.

Descriptive geometry problems range from relatively simple to very complex. The solution to most of these problems can be found through the utilization of information in this section. Descriptive geometry techniques build on and broaden the understanding of orthographic projection.

Some applications that require descriptive geometry solutions are:

  1. Maintaining clearance between a tubular structure and the parts supported by the structure
  2. Determining the cutout shape and size for a steering column that passes through an automobile firewall
  3. Checking the clearance between a power line and a rooftop
  4. Determining visibility of lines in a complex drawing.

Revolutions

Revolutions are used to aid in drawing the true-shape view of features that are not in the principal planes. Their use is similar to auxiliary views since auxiliaries and revolutions can both be used to determine true shape. The procedures used for drawing revolutions are quite different from those used for auxiliaries.

Revolutions are drawn by orienting the object in such a manner as to position the desired feature in an appropriate position relative to the lines of sight in existing views. The object features are revolved around an axis of revolution. Auxiliary views are drawn by assuming viewer positions (lines of sight) that result in the correct relationship between the viewer and object.