Line is one important aspect of technical drawing. In Engineering Graphics, the details of various objects are drawn by different types of lines. Each line has a definite meaning and sense to convey. Lines are always used to construct meaningful drawings. Various types of lines are used to construct drawing, each line used in some specific sense. Lines are drawn based on some standard conventions mentioned in BIS (SP 46:2003). A line may be curved, straight, continuous or segmented. It may be drawn as thin or thick. Engineering drawing consists of organized combination of different types of lines. Lettering plays an important role as far as logical comprehension of the drawing is concerned, particularly for those parts of the drawing which cannot be shown by lines. A well meaning drawing must be associated with clean dimensioning with good letter quality.
Line Thickness
The thicknesses of lines are varied according to the drawing and are finalized either by ink or by pencil. Thickness of the line should be chosen according to the size and type of the drawing from the following range. (IS:10714-1983) 0.18, 0.25, 0.35, 0.5, 0.7, 1, 1.4 & 2 mm.
Inked Drawings
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.
Pencil Drawings
For drawings finalized with pencil, the lines can be divided into two line-groups. 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.
Types of Line
Various types of lines used in general engineering drawing are shown in Table 1 as described by SP 46:2003.
Table 1 Types of Line as per SP 46:2003
Fig. 1 (a) (b) (c) Representation of Different Types of Line
1) Outlines
Lines drawn to represent visible edges and surface boundaries of objects are known as outlines or object lines or principal lines. These are represented by continuous thick lines.
2) Dimension Lines
Continuous thin lines, used for giving dimensions of the drawing, are known as dimension lines. A dimension line is terminated at its outer end with an arrow head touching the outline, extension line or centre line.
3) Extension Lines or Projection Lines
These are continuous thin lines used for dimensioning an object. They extend by about 3 mm beyond the dimension lines.
4) Construction Lines
These are thin continuous lines used for construction of objects.
5) Section Lines or Hatching Lines
These are thin continuous lines used for showing the section evidently. They are uniformly spaced thin lines drawn at an angle of 45 degree to the main outline of the section. The spacing between the lines is generally 1 mm to 2 mm.
6) Leader or Pointer Lines
These are continuous thin lines and are drawn to connect a note with the specific feature in the drawing.
7) Short-Break Lines
These are continuous, thin and wavy freehand lines drawn to show the break of an object for a short length. These are also used to show irregular boundaries.
8) Long-Break Lines
These are thin ruled lines provided with short zigzags at suitable intervals. They are drawn to show long breaks.
9) Hidden or Dotted Lines
These are closely and evenly spaced dashes lines of equal lengths. They are of medium thickness and are used to show the invisible or hidden parts of the object on the drawing.
10) Centre Lines
These are thin, long, chain lines composed of alternatively long and short dashes spaced at an approximate distance of 1 mm. The proportion of long and short dashes is 6:1 to 8:1. The short dashes are about 1.5 mm long. These are used to indicate the axes of cylindrical, conical and spherical objects. These are also used to show the centres of circles and arcs. Centre lines should extend for a short distance beyond the outlines to which they refer. Locus lines, extreme positions of movable parts and pitch circles are also shown by these lines.
11) Cutting-Plane Lines
These are long, thin chain line with thick ends. These are used to show the location of cutting plane.
12) Chain Thick
These lines are used to indicate special treatment on the surface.
13) Chain Thick Double-Dashed
These lines are used to show outlines of adjacent parts, alternative and extreme positions of movable parts, centroidal lines and parts situated in front of the cutting plane.
14) Hatching Lines
Hatching lines are the inclined parallel lines. The minimum space between these lines should be more than twice the thickness of the heaviest line in the drawing. It is recommended that these spacing should never be less than 0.7 mm. For showing the limits of partial or interrupted views and sections continuous thin free hand lines or continuous thin straight lines with zig-zag are used.
0 comments:
Post a Comment