An
engineering drawing is a type of drawing that is technical in nature, used to fully and clearly define requirements for
engineered items, and is usually created in accordance with standardized conventions for layout, nomenclature, interpretation, appearance (such as typefaces and line styles), size, etc. Its purpose is to accurately and unambiguously capture all the geometric features of a product or a component. The end goal of an
engineering drawing is to convey all the required information that will allow a manufacturer to produce that component.
Engineering
drawings are often referred to as "blueprints" or "bluelines". However, the terms are rapidly becoming an anachronism, since most copies of engineering drawings that were formerly made using a chemical-printing process that yielded graphics on blue-colored paper or, alternatively, of blue-lines on white paper, have been superseded by more modern reproduction processes that yield black or multicolour lines on white paper. The process of producing engineering drawings, and the skill of producing them, is often referred to as technical drawing, although technical drawings are also required for disciplines that would not ordinarily be thought of as parts of engineering.
Common features of engineering drawings
Drawings convey the following critical information:
Geometry – the shape of the object; represented as views; how the object will look when it is viewed from various standard directions, such as front, top, side, etc.
Dimensions – the size of the object is captured in accepted units.
Tolerances – the allowable variations for each dimensions.
Material – represents what the item is made of.
Finish – specifies the surface quality of the item, functional or cosmetic.
For example, a mass-marketed product usually requires a much higher surface quality than, say, a component that goes inside industrial machinery.
A variety of line styles are used to graphically represent physical objects. Types of lines include the following:
visible – are continuous lines used to depict edges directly visible from a particular angle.
hidden – are short-dashed lines that may be used to represent edges that are not directly visible.
center – are alternately long- and short-dashed lines that may be used to represent the axes of circular features.
cutting plane – are thin, medium-dashed lines, or thick alternately long- and double short-dashed that may be used to define sections for section views.
section – are thin lines in a parallel pattern used to indicate surfaces in section views resulting from "cutting."
Section lines are commonly referred to as "cross-hatching."
Lines can also be classified by a letter classification in which each line is given a letter. Type A lines are used to show the outline of the feature of an object. They are the thickest lines on a drawing and done with a pencil softer than HB.
Type B lines are dimension lines and are used for dimensioning, projecting, extending, or leaders. A harder pencil should be used, such as a 2H.
Type C lines are used for breaks when the whole object is not shown. They are freehand drawn and only for short breaks. 2H pencil
Type D lines are similar to Type C, except they are zigzagged and only for longer breaks. 2H pencil
Type E lines are used to indicate hidden outlines of internal features of an object. They are dotted lines. 2H pencil
Type F lines are Type F
lines, except they are used for drawings in electrotechnology. 2H pencil
Type G lines are used for centre lines. They are dotted lines, but a long line of 10–20mm, then a gap, then a small line of 2mm. 2H pencil
Type H lines are the same as Type G, except that every second long line is thicker. They are used to indicate the cutting plane of an object. 2H pencil
Type K lines are used to indicate the alternate positions of an object and theline taken by that object. They are drawn with a long line of 10–20mm, then a small gap, then a small line of 2mm, then a gap, then another small line. 2H pencil.