American National Standards Institute (ANSI)

ANSI has been a leader in the voluntary standards system of the United States. This organization has provided a forum for private and public sectors to collectively work together toward the development of national standards. Efforts to coordinate national standards date back to 1911. In 1916, the following agencies were instrumental in establishing a national body to oversee the development of national standards:

The American Institute of Electrical Engineers (now IEEE)

The American Society of Mechanical Engineers (ASME)

The American Society of Civil Engineers (ASCE)

The American Institute of Mining, Metallurgical, and Petroleum Engineers (AIME)

The American Society for Testing and Materials (ASTM)

These organizations along with the U.S. Departments of War, Navy, and Commerce were the founders of the American Engineering Standards Committee (AESC). This organization led to the formation of the American National Standards Institute (ANSI) in 1969. Throughout its history, ANSI has continued to coordinate national and international efforts to approve voluntary standards. Over the past 85 years, this organization has maintained its strong ties with the original founding organizations and others to become one of the most highly regarded standards systems in the world.

Specific standards are revised periodically by a committee of industry leaders who also serve as representatives of various industry service organizations. For example, the vice president of engineering at Xerox Corporation might serve on the board of the American Society of Mechanical Engineers (ASME). These committee members revise such standards as Drawing Sheet Size and Format, Dimensioning and Tolerancing, and Line Conventions and Lettering. The standards should be readily available in the classroom so that students can develop engineering drawings that adhere to these standards. Specific standards must be available for each content area—mechanical, electrical, or civil. The following section lists some commonly used mechanical engineering standards.

American Society of Mechanical Engineers (ASME)

The American Society of Mechanical Engineers conducts one of the world’s largest publishing operations to produce technical and engineering documents to establish standards. ASME documents are recognized worldwide for industrial and manufacturing codes and standards. Some of the popular documents on engineering standards include:

• Y14.2M-1992 Line Conventions and Lettering

• Y14.5.2-2000-2001 Certification of Geometric Dimensioning and Tolerancing

• Y14.38-1999 Abbreviations and Acronyms

• Y14.1-1980 (R1987) Drawing Sheet Size and Format

• Y14.1M-1992 Metric Drawing Sheet Size and Format

• Y14.3M-1994 Multiview and Sectional View Drawings

International Organization for Standardization (ISO)

The International Organization for Standardization is an organized network of the national standards institutes of 148 countries. It is a nongovernmental organization, but its members are not. ISO has a unique mission in acting as a bridge between business/industry and consumers/users. ISO has published more than 13,700 International Standards ranging from engineering drawing to medical devices. ISO is also responsible for providing a framework for quality management throughout the processes of producing and delivering products and services by implementing ISO 9000.

Some of the more commonly used ISO drawing standards are:

ISO 10135:1994

Technical drawings—Simplified representation of molded, cast, and forged parts

ISO 10209-1:1992

Technical product documentation—Vocabulary—Part 1: Terms relating to technical drawings: general and types of drawings

ISO 10209-2:1993

Technical product documentation—Vocabulary—Part 2: Terms relating to projection methods

Many companies, such as General Electric and General Motors, develop their own standards by incorporating the use of ANSI, ASME, and ISO criteria. In this way, national standards can be incorporated with company standards to meet specific requirements.

Standard Text Heights

The typical standard height for text on a drawing is 1/8″. Fractions need to be created 1/4″ tall. These are general guidelines for text height. Text height should be increased or decreased based on individual situations.

To achieve these final printed and plotted text sizes, it is necessary to create the text within the AutoCAD drawing at the correct size. The following table lists examples of the relationship between sheet size, plot scale, scale factor, model space drawing area, and text height.

Calculating the Scale Factor

The drawing scale factor used to scale annotation features up and down is always the reciprocal of the plot or viewport scale. The easiest way to calculate the reciprocal value of the plot/viewport scale is to first put all values into the same units and then cross-multiply. For example, to calculate the drawing scale factor for the architect’s scale 1/8″ = 1′-0″, you would first convert all values to inches and display them all as stacked fractions:

Then cross-multiply by multiplying the denominator on the left side of the equal sign (=) (8) times the numerator on the right side (12) and then the numerator on the left (1) times the denominator on the right (1) for a result of 96/1. The last step is to reduce the fraction by dividing the denominator (1) into the numerator (96) for a scale factor of 96.

Notes and Locating Text on a Drawing

Notes and text are necessary to supplement a fully dimensioned engineering drawing. Notes should be clear and concise to avoid any misinterpretation. Notes are always lettered horizontally on the sheet and systematically organized. Do not place notes and text in crowded or busy locations on the drawing. Avoid placing notes between orthographic views. Use only standard ANSI or ASME abbreviations with a note.

Notes are classified as General Notes or Local/Specific Notes.

General Notes. General notes apply to the entire drawing. General notes are typically placed in the lower right corner of the drawing above or to the left of the title block. Title blocks may provide general information about the drawing such as tolerance, material, or treatment. General notes may be placed below the view to which the note applies.

Local/Specific Notes. Local notes provide specific detailed information. These notes are placed adjacent to the specific feature they describe. Local notes may be connected with a leader. The leader arrow or dot will touch the detail and end with a note.

Leaders

Leaders should be attached at the middle front of the first word of the note or after the last word of the note. Leaders to a circle should be developed radially. The slanted line of the leader should be aimed at the center of the circle or arc. A shoulder or horizontal line of the leader is optional. Leader lines should not cross each other. Refer to the following standard for additional information:

Y14.5.2-2000-2001 Certification of Geometric Dimensioning and Tolerancing

Standard Feature Sizes

Figure A-12 illustrates some common terms and distances to consider when dimensioning standard feature sizes.

Mechanical Style

There are two systems of placing dimensions on a drawing: the unidirectional system and the aligned system. In the unidirectional system, all the dimension figures and notes are lettered horizontally on the sheet (see Figure A-12). This is the preferred system of the American National Standards Institute. The mechanical style of dimensioning illustrates the unidirectional system. The unidirectional system is widely used because it is easy to read and interpret on large drawings. The unidirectional system is the standard default dimensioning system in AutoCAD.

Architectural Style

The architectural style of dimensioning (see Figure A-13) illustrates the aligned system. The aligned system has all the dimension figures aligned with the dimension line. Many of the dimension figures are horizontal on the sheet and some are aligned or turned. Any rotated figures are to be read from the right side of the sheet.

The architectural style of dimensioning has numbers placed on top of an unbroken dimension line. The dimension line typically ends with a slash, dot, or arrowhead. The numbers normally are designated with inch (″) and foot (′) symbols.

Linetypes and Thicknesses

Linetypes that are used within AutoCAD should correspond with the standard ANSI linetypes and thicknesses. Every line that is used on a technical drawing has a specific meaning and needs to be illustrated in a certain way. The American National Standards Institute has established the Line Conventions and Lettering standard ANSI Y-14.2M-1992. This standard describes the size, application, and construction of various lines that are used in creating engineering drawings. Figure A-14 details various linetypes and their applications.

It should be noted that the line widths established in this illustration are approximate, and the actual width is governed by the size and style of the drawing. Large drawings will need to have wider lines, and drawings that are reduced in size will need to have smaller line widths than specified in this illustration. The ANSI Y-14.2M standard and this illustration should be used as a guide to produce crisp and legible engineering drawings from AutoCAD.

Linetypes are described in an AutoCAD file called ACAD.LIN. These linetypes should be loaded into the AutoCAD drawing file and assigned correct lineweights that correspond with the ANSI standards. The AutoCAD command LTSCALE should be used to adjust the size of the linetypes to match the size of the drawing area in AutoCAD. Figure A-15 shows examples of AutoCAD’s standard linetypes, which are defined in the ACAD.LIN file.

Specifying the Scale on a Drawing

For machine drawings, the scale indicates the ratio of the size of the drawn object to its actual size, irrespective of the unit of measurement used. The recommended practice is to letter full-size or 1:1; half-size or 1:2; and similarly for other reductions. Expansion or enlargement scales are given as 2:1 or 2:3; 3:1 or 3:3; 5:1 or 5:3; 10:1 or 10:3; and so on.

The various scale calibrations available on the metric scale and the engineers’ scale provide almost unlimited scale ratios. The preferred metric scale ratios appear to be 1:1, 1:2, 1:5, 1:10, 1:20, 1:50, 1:100, and 1:200.

Map scales are indicated in terms of fractions, such as scale 162500, or graphically, such as .

Section Lining

Section-lining symbols (see Figure A-17) have been used to indicate specific materials. These symbols represent general material types only, such as cast iron, brass, and steel. Now, however, because there are so many different types of materials, and each has so many subtypes, a general name or symbol is not enough. For example, there are hundreds of different kinds of steel. Since detailed specifications of material must be lettered in the form of a note or in the title strip, the general-purpose (cast-iron) section lining may be used for all materials on detail drawings (single parts).

Section-lining symbols may be used in assembly drawings in cases where it is desirable to distinguish different materials; otherwise, the general-purpose symbol is used for all parts.

CAD programs usually include a library that allows the user to select from a variety of section-lining patterns, making it easy to indicate various types of material rather than using the generic cast-iron symbol for all sectioned parts.

ANSI has standardized many section lines that are used for sectional drawing. AutoCAD uses the HATCH command to insert hatch patterns that are used to illustrate these section lines. The following table lists the ANSI section line with corresponding AutoCAD hatch pattern, as seen in Figure A-17.