Engineering drawings

 types of lines

(1) line thickness: The thicknesses of lines are varied according to the drawing and are finalized either by ink or by pencil. 

(2) Inked drawings: The thicknesses of lines in various groups are shown in table 3-1. The line-group is designated according to the thickness of the thickest line. For any particular drawing a line-group is selected according to its size and type. All lines should be sharp and dense so that good prints can be reproduced

(3) Pencil drawings: For drawings finalized with pencil, the lines can be divided into two line-groups as shown in table 3-2. It is important to note that in the finished drawing, all lines except construction lines should be dense, clean and uniform. Construction lines should be drawn very thin and faint and should be hardly visible in the finished drawing.

  Outlines (A): Lines drawn to represent visible edges and surface boundaries of objects are called outlines or principal lines. They are continuous thick or wide lines (fig. 3-2). (2) lines (A): They are continuous thick or wide lines along which the prints are trimmed [fig. 2-1 (a)]. (3) (B): These lines are continuous thin lines. They are terminated at the outer ends by pointed arrowheads touching the outlines, extension lines or centre lines (fig. 3-2). (4) Extension or projection lines (B): These lines also are continuous thin lines. They extend by about 3 mm beyond the dimension lines (fig. 3-2). (5) Construction lines (B): These lines are drawn for constructing figures. They are shown in geometrical drawings only. They are continuous thin light lines. (6) or section lines (B): These lines are drawn to make the section evident. They are continuous thin lines and are drawn generally at an angle of 45° to the main outline of the section. They are uniformly spaced about 1 mm to 2 mm apart (fig. 3-2). (7) or pointer lines (B): Leader line is drawn to connect a note with the feature to which it applies. It is a continuous thin line (fig. 3-2). {8) lines (B): Perfectly rectangular working space is determined by drawing the border lines [fig. 2-1 (a)]. They are continuous thin lines. (9) lines (C): These lines are continuous, thin and wavy. They are drawn freehand and are used to show a short break, or irregular boundaries (fig. 3-3). (1 long-break lines (D): These lines are thin ruled lines with short zigzags within them. They are drawn to show long breaks (fig. 3-3). (11) or dotted lines (E or F): Interior or hidden edges and surfaces are shown by hidden lines. They are also called dotted lines. They are of medium thickness and made up of short dashes of approximately equal lengths of about 2 mm spaced at equal distances of about 1 mm. When a hidden line meets or intersects another hidden line or an outline, their point of intersection or meeting should be clearly shown (fig. 3-2). (12) Centre lines (G): Centre lines are drawn to indicate the axes of cylindrical, conical or spherical objects or details, and also to show the centres of circles and arcs. They are thin, long, chain lines composed of alternately long and dot spaced approximately 1 mm apart. The long dashes are about 9 to 12 mm. Centre lines should extend for a short distance beyond the outlines to which they refer. For the purpose of dimensioning or to correlate the views they may be extended as required. The point of intersection between two centre lines must always be indicated. Locus lines, extreme positions of movable parts and pitch circles are also