2.4 Types of Lines Used on a Drawing
2.4 Types of Lines Used on a Drawing
Refer to Figure 2-12 to see the various types of lines that may be used on a drawing. Lines on an original drawing are always made as black as possible. The thickness and shape of the various lines, however, will vary as their purpose varies on the drawing.
2.4.1 Object Lines and Hidden Lines
The outline of the object is a solid black line called an object lineA solid black line that defines the outline of an object.. It has a thickness of about 0.024″ (0.6mm). Lines hidden from view by material in front of them are called hidden edge linesDashed lines that represent any line of an object that is hidden from view by material in front of it.. They are lines that are made up of a series of 1/8″ (3.2mm) long Page 41 dashes spaced 1/16″ (1.5mm) apart. These hidden lines are usually drawn about 0.020″ (0.50mm) thick.
2.4.2 Center Lines
The center of a radius, circle, or cylinder is marked by a center lineA line, composed of long and short dashes, that is drawn through the exact center of a circular part or hole in a drawing.. This is a line about 0.012″ (0.3mm) thick. It is made up of a series of 3/4″ (19mm) long and 1/8″ (3.2mm) short dashes with a 0.06″ (1.5mm) space between them. A centerline runs through the exact center of a circular part or hole.
2.4.3 Extension Lines
The ends or terminal points of a dimensioned line are marked by lines called extension lines. They are the same thickness as a centerline, but are solid lines. The size of a given line or feature on the object is usually placed between extension lines. On very small dimensions, when a number cannot be placed between the dimension lines, the dimension is placed at the end of one of the extension lines.
2.4.4 Dimension Lines
Dimension lines and dimensions are placed about 1/2″ (12.7mm) away from the outer edge of the object. A long, thin arrowhead appears at each end of a dimension lineThin lines that are placed on each side of a dimension and terminate in arrowheads at the extension lines.. Dimension lines generally stretch between extension lines, with a gap in the center for the dimension. When a large number of dimensions are required, each dimension line is placed farther from the object at 1/2″ (12.7mm) intervals. Dimension lines are 0.012″ (0.3mm) thick.
2.4.5 Cutting Plane Lines
Occasionally, it is necessary to show the inside features of an object. To do so, it may be necessary to theoretically cut through the object at some point. The direction of the cutting line is shown with a line called a cutting plane lineHeavy dashed line that shows a theoretical cut through an object.. This is the thickest line that may appear on a drawing. It is made up of a series of 3/4″ long (19mm) and double lines 1/8″ (3.2mm) long that are about 0.040″ (1mm) thick.
2.4.6 Section Lines
Section linesThin lines, 0.012″ (0.3mm) thick, that show solid, cutaway surfaces in a section view. are thin lines, 0.012″ (0.3mm) thick, that show solid, cutaway surfaces in a section view. The section lines are drawn at a 45° angle to the object lines. The section lines in adjacent parts are drawn in opposite directions, and different line styles can be used to indicate different materials. Thin parts, such as sheet metal or gaskets, do not typically include section lines.
2.4.7 Leader Lines
The size of a corner radius or size for a hole is given by using a leader line that points to the edge of the circle and “leads” the reader out to a clear area on the drawing where a diameter or dimension is given. The leader line is aligned from the center of the hole or radius and touches the circle or the arc. See the example in the top view of Figure 2-12.
The difference in line types is used so that a person looking at a drawing first sees the outline of the object, which stands out because of the heavy lines used. Then, by following lines and points from view to view, the person reading the print can find the extension lines and dimension lines, and finally the dimension that he or she is looking for.