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ALPHABET OF LINES

To read a drawing, you must know how engineers use lines, dimensions, and notes to communicate their ideas on paper. In this section, we briefly discuss each of these drawing elements. The "Alphabet of Lines" is a list of line symbols that are used on technical drawings to represent the shape and describe the size of an object. Drawing or sketching is a universal language used to convey all necessary information to the individual who will fabricate or assemble an object. Prints are also used to illustrate how various equipment is operated, maintained, repaired, or lubricated.

Each of the following lines is drawn at different thickness or darkness for contrast as well as according to the importance of the line. If two lines fall on top of one another (coinside), the more important line is shown. Object (visible) lines take presidence over hidden lines and center lines; and hidden lines take presidence over center lines. The list below gives the name of the line; explains how the line is used; indicates the appropriate thickness or darkness; and provides the recommended pencil weight for drawing the line.

Object Lines (A, fig. 3-1). Object or Visiblel lines represent the visible edges or outlines of an object.

Hidden Lines (A, fig. 3-1). Hidden lines are made of short dashes which represent hidden edges of an object.

Center Lines (B, fig. 3-1). Center lines are made with alternating short and long dashes. A line through the center of an object is called a center line.

Cutting Plane Lines (B, fig. 3-1). Cutting plane lines are dashed lines, generally of the same width as the full lines, extending through the area being cut. Short solid wing lines at each end of the cutting line project at 90 degrees to that line and end in arrowheads which point in the direction of viewing. Capital letters or numerals are placed just beyond the points of the arrows to designate the section.

Dimension Lines (A, fig. 3-1). Dimension lines are fine full lines ending in arrowheads. They are used to indicate the measured distance between two points.

Extension Lines (A, fig. 3-1). Extension lines are fine lines from the outside edges or intermediate points of a drawn object. They indicate the limits of dimension lines.

Break Lines (C, fig. 3-1). Break lines are used to show a break in a drawing and are used when it is desired to increase the scale of a drawing of uniform cross section while showing the true size by dimension lines. There are two kinds of break lines: short break and long break. Short break lines are usually heavy, wavy, semiparallel lines cutting off the object outline across a uniform section. Long break lines are long dash parallel lines with each long dash in the line connected to the next by a "2" or sharp wave line.

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