Alphabet of Lines

Alphabet of Lines

Industry standard classifying the different types of lines used in drawings.

Developed by the American Society of Mechanical Engineers (ASME).

Lines are classified by line thickness and drawn thin or thick.

Alphabet of Lines

Alphabet of Lines

The American National Standards Institute (ANSI) drafting standard applies.• An approximate 2:1 line width ratio is used for manually

drawn thick and thin lines.• For CAD drawings, a single line width is acceptable.

Thick lines are typically drawn with a 0.7 mm or 0.9 mm mechanical pencil.

Thin lines are typically drawn with a 0.3 mm or 0.5 mm mechanical pencil.

Alphabet of Lines

Construction Lines

Used to initially lay out a drawing. Drawn very light and thin so they are

barely visible. Drawn with a 0.3 mm pencil or a

sharpened drafting pencil with a hard lead.

Guidelines

Used to make freehand lettering uniform in size.

Drawn very light and thin so they are barely visible.

Drawn with a 0.3 mm pencil or a sharpened drafting pencil with a hard lead.

Visible Lines

Used to represent the visible edges of an object.

Also called object lines. Drawn thick and dark. Drawn with a 0.7 mm or 0.9 mm

drafting pencil with a soft lead.

Hidden Lines

Used to represent edges hidden from view.

Drawn as thin, dark lines. Drawn as 3 mm dashes about 1.5 mm

apart. Spacing can vary slightly.

Centerlines

Used to show the center of circles and arcs. Drawn as thin lines. Drawn using two long dashes and a short

dash separated by a 1.5 mm gap. The short dash is drawn about 3 mm long at

the center point. The long dash extends beyond the circle.

Dimension Lines

Used for dimensioning and notes. Drawn as thin lines. Drawn with arrowheads on each end

and placed between extension lines. A line break provides space for the

dimension.

Extension Lines

Used to extend dimensions from the related objects.

Drawn as thin lines. Drawn with a short space between the

object and line. Extend about 3 mm beyond the

dimension line.

Leaders

Used to point to notes or dimensions. Drawn as thin lines. Consist of an arrowhead and angled

line connected to a shoulder.

Cutting-Plane Lines

Used to indicate where an imaginary cut is made on an object.

Refer to a section view. Drawn as thick lines. Arrows indicate the direction of view.

Viewing-Plane Lines

Used to indicate an area related to a separate view.

Drawn as thick lines. Arrows indicate the direction of view.

Section Lines

Used to represent a surface cut by a cutting-plane line.

Drawn as thin lines equally spaced at 45.

Spacing between lines varies.

Break Lines

Used to indicate part of the object has been removed.

Short break lines are drawn thick. Long break lines are drawn thin with

freehand “zigzags.”

Phantom Lines

Used to indicate alternate positions for moving parts or repeated details.

Drawn as thin lines. Drawn as long dashes connected by

two short (3 mm) dashes with spacing of approximately 1.5 mm.

Chain Lines

Used to indicate a type of treatment for surfaces.

Drawn as thick lines. Drawn as alternating long and short

dashes.

Orthographic Projection

A standard form of drawing using the alphabet of lines.

Several two-dimensional (2D) views of the three-dimensional (3D) object provide a complete description.

Orthographic drawings are also known as multiview drawings.

Projecting Views

Each object side or view is projected onto an imaginary projection plane.

Each view has a specific location in relation to the others.

To visualize, place an imaginary glass box around an object so each side becomes a view.