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.