An engineering drawing, a type of technical drawing Technical drawing, also known as drafting, is the academic discipline of creating standardized technical drawings by architects, interior designers, drafters, design engineers, and related professionals. Standards and conventions for layout, line thickness, text size, symbols, view projections, descriptive geometry, dimensioning, and notation are, is created within the technical drawing discipline, and used to fully and clearly define requirements for engineered Engineering is the discipline, art and profession of acquiring and applying technical, scientific, and mathematical knowledge to design and implement materials, structures, machines, devices, systems, and processes that safely realize a desired objective or invention items.

Contents 1 Overview 2 Engineering drawings: common features 2.1 Line styles and types 2.2 Multiple views and projections 2.2.1 Orthographic projection 2.2.2 Auxiliary projection 2.2.3 Isometric projection 2.2.4 Oblique projection 2.2.5 Perspective 2.3 Scale 2.4 Showing dimensions 2.5 Sizes of drawings 2.6 Technical lettering 3 Example of an engineering drawing 4 See also 5 References 6 Further reading 7 External links

Overview

Engineering drawings are usually created in accordance with standardized conventions for layout, nomenclature, interpretation, appearance (such as typefaces In typography, a typeface is a set of one or more fonts, in one or more sizes, designed with stylistic unity, each comprising a coordinated set of glyphs. A typeface usually comprises an alphabet of letters, numerals, and punctuation marks; it may also include ideograms and symbols, or consist entirely of them, for example, mathematical or map- and line styles), size, etc. One such standardized convention is called GD&T Geometric dimensioning and tolerancing is a symbolic language used on engineering drawings and computer generated three-dimensional solid models for explicitly describing nominal geometry and its allowable variation.

The purpose of such a drawing 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 used to be created by hand using tools such as pencils, ink, straightedges A straightedge is a tool with an edge free from curves, or straight, used for transcribing straight lines, or checking the straightness of lines. If it has equally spaced markings along its length it is usually called a ruler, T-squares A T-square is a technical drawing instrument that is primarily used as a guide for drawing horizontal lines on a drafting table. It is used by draftsmen. It is also used to guide the triangle that draws vertical lines. Its name comes from the general shape of the instrument where the horizontal member of the T slides on the side of the drafting, French curves A French curve is a template made out of plastic, metal or wood composed of many different curves. It is used in manual drafting to draw smooth curves of varying radii, triangles, rulers A ruler, sometimes called a rule or line gauge, is an instrument used in geometry, technical drawing, printing and engineering/building to measure distances and/or to rule straight lines. Strictly speaking, the ruler is essentially a straightedge used to rule lines[citation needed] and the calibrated instrument used for determining measurement is, scales, and erasers. Today they are usually done electronically with computer-aided design Computer-aided design is the use of computer technology for the design of objects, real or virtual. CAD often involves more than just shapes. As in the manual drafting of technical and engineering drawings, the output of CAD often must convey also symbolic information such as materials, processes, dimensions, and tolerances, according to (CAD).

The drawings are still often referred to as "blueprints A blueprint is a type of paper-based reproduction usually of a technical drawing, documenting an architecture or an engineering design. More generally, the term "blueprint" has come to be used to refer to any detailed plan" or "bluelines In a variety of combination's and strengths, these two chemicals are mixed together in water and coated onto paper. The resulting coating is then dried yielding the specially treated paper commercially sold as Diazo paper. This solution can also be applied to polyester film or to vellum", although those terms are anachronistic An anachronism—from the Greek ανά and χρόνος (chronos: time)—is an error in chronology, especially a chronological misplacing of persons, events, objects, or customs in regard to each other. The item is often an object, but may be a verbal expression, a technology, a philosophical idea, a musical style, a material, a custom, or from a literal perspective, 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 more generic term "print" is now in common usage in the U.S. to mean any paper copy of an engineering drawing.

The process of producing engineering drawings, and the skill of producing them, is often referred to as technical drawing Technical drawing, also known as drafting, is the academic discipline of creating standardized technical drawings by architects, interior designers, drafters, design engineers, and related professionals. Standards and conventions for layout, line thickness, text size, symbols, view projections, descriptive geometry, dimensioning, and notation are or drafting, although technical drawings are also required for disciplines that would not ordinarily be thought of as parts of engineering.

Engineering drawings: common features

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 angles, such as front, top, side, etc.
• Dimensions – the size of the object is captured in accepted units.
• tolerances Dimensions, properties, or conditions may vary within certain practical limits without significantly affecting functioning of equipment or a process. Tolerances are specified to allow reasonable leeway for imperfections and inherent variability without compromising performance – the allowable variations for each dimension.
• 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.

Line styles and types

Standard engineering drawing line types

A variety of line styles 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 In geometry, a cross-section is the intersection of a figure in 2-dimensional space with a line, or of a body in 3-dimensional space with a plane, etc. More plainly, when cutting an object into slices one gets many parallel cross-sections.
• section – are thin lines in a pattern (pattern determined by the material being "cut" or "sectioned") 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 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 indicate hidden outlines of internal features of an object. They are dotted lines. 2H pencil
• Type F lines are Type F[typo] 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 10–20 mm, then a gap, then a small line of 2 mm. 2H pencil
• Type H lines are the same as Type G, except that every second long line is thicker. They indicate the cutting plane of an object. 2H pencil
• Type K lines indicate the alternate positions of an object and the line taken by that object. They are drawn with a long line of 10–20 mm, then a small gap, then a small line of 2 mm, then a gap, then another small line. 2H pencil.

Multiple views and projections

Image of a part represented in First Angle Projection Symbols used to define whether a projection is either Third Angle (right) or First Angle (left). Isometric view of the object shown in the engineering drawing below. Main article: Graphical projection Graphical projection is a protocol by which an image of an three-dimensional object is projected onto a planar surface without the aid of mathematical calculation, used in technical drawing

In most cases, a single view is not sufficient to show all necessary features, and several views are used. Types of views include the following:

Orthographic projection

The orthographic projection Orthographic projection is a means of representing a three-dimensional object in two dimensions. It is a form of parallel projection, where the view direction is orthogonal to the projection plane, resulting in every plane of the scene appearing in affine transformation on the viewing surface. It is further divided into multiview orthographic shows the object as it looks from the front, right, left, top, bottom, or back, and are typically positioned relative to each other according to the rules of either first-angle or third-angle projection The views are positioned relative to each other according to either of two schemes: first-angle or third-angle projection. In each, the appearances of views may be thought of as being projected onto planes that form a 6-sided box around the object.

• First angle projection is the ISO standard and is primarily used in Europe. The 3D object is projected into 2D "paper" space as if you were looking at an X-ray of the object: the top view is under the front view, the right view is at the left of the front view.
• Third angle projection is primarily used in the United States and Canada, where it is the default projection system according to BS 8888:2006, the left view is placed on the left and the top view on the top.

Not all views are necessarily used, and determination of what surface constitutes the front, back, top and bottom varies depending on the projection used.

Auxiliary projection

An auxiliary view is an orthographic view that is projected into any plane other than one of the six principal views.^[1] These views are typically used when an object contains some sort of inclined plane. Using the auxiliary view allows for that inclined plane (and any other significant features) to be projected in their true size and shape. The true size and shape of any feature in an engineering drawing can only be known when the Line of Sight (LOS) is perpendicular to the plane being referenced.

Isometric projection

The isometric projection Isometric projection is a form of graphical projection, more specifically, a form of axonometric projection. It is a method of visually representing three-dimensional objects in two dimensions, in which the three coordinate axes appear equally foreshortened and the angles between any two of them are 120 degrees show the object from angles in which the scales along each axis of the object are equal. Isometric projection corresponds to rotation of the object by ± 45° about the vertical axis, followed by rotation of approximately ± 35.264° [= arcsin(tan(30°))] about the horizontal axis starting from an orthographic projection view. "Isometric" comes from the Greek for "same measure." One of the things that makes isometric drawings so attractive is the ease with which 60 degree angles can be constructed with only a compass A compass or pair of compasses is a technical drawing instrument that can be used for inscribing circles or arcs. As dividers, they can also be used as a tool to measure distances, in particular on maps. Compasses can be used for mathematics, drafting, navigation, and other purposes and straightedge A straightedge is a tool with an edge free from curves, or straight, used for transcribing straight lines, or checking the straightness of lines. If it has equally spaced markings along its length it is usually called a ruler.

Isometric projection Isometric projection is a form of graphical projection, more specifically, a form of axonometric projection. It is a method of visually representing three-dimensional objects in two dimensions, in which the three coordinate axes appear equally foreshortened and the angles between any two of them are 120 degrees is a type of axonometric projection Axonometric projection is a type of parallel projection, more specifically a type of orthographic projection, used to create a pictorial drawing of an object, where the object is rotated along one or more of its axes relative to the plane of projection. The other two types of axonometric projection are:

• Dimetric projection Axonometric projection is a type of parallel projection used to create a pictorial drawing of an object, where the object is rotated along one or more of its axes relative to the plane of projection. Axonometric projection is a type of orthographic projection where the plane or axis of the object depicted is not parallel to the projection plane
• Trimetric projection Axonometric projection is a type of parallel projection, more specifically a type of orthographic projection, used to create a pictorial drawing of an object, where the object is rotated along one or more of its axes relative to the plane of projection

Oblique projection

An oblique projection Oblique projection is a simple type of graphical projection used for producing pictorial, two-dimensional images of three-dimensional objects is a simple type of graphical projection used for producing pictorial, two-dimensional images of three-dimensional objects:

• it projects an image by intersecting parallel rays (projectors)
• from the three-dimensional source object with the drawing surface (projection plan).

In both oblique projection and orthographic projection Orthographic projection is a means of representing a three-dimensional object in two dimensions. It is a form of parallel projection, where the view direction is orthogonal to the projection plane, resulting in every plane of the scene appearing in affine transformation on the viewing surface. It is further divided into multiview orthographic, parallel lines of the source object produce parallel lines in the projected image.

Perspective

Perspective is an approximate representation on a flat surface, of an image as it is perceived by the eye. The two most characteristic features of perspective are that objects are drawn:

• Smaller as their distance from the observer increases
• Foreshortened: the size of an object's dimensions along the line of sight are relatively shorter than dimensions across the line of sight.

Scale

Main articles: Architect's scale An architect's scale is a specialized ruler. It is used in making or measuring from reduced scale drawings, such as blueprints and floor plans. It is marked with a range of calibrated scales, Engineer's scale An engineer's scale is a tool for measuring distances and transferring measurements at a fixed ratio of length. It is commonly made of plastic and is just over 12 inches long, but with only 12 inches of markings, leaving the ends unmarked so that so that the first and last measuring ticks do not wear off. It is used in making engineering drawings,, and Metric scale

Plans are usually "scale drawings", meaning that the plans are drawn at specific ratio In mathematics, a ratio expresses the magnitude of quantities relative to each other. Specifically, the ratio of two quantities indicates how many times the first quantity is contained in the second and may be expressed algebraically as their quotient. Example: For every Spoon of sugar, you need 2 spoons of flour relative to the actual size of the place or object. Various scales may be used for different drawings in a set. For example, a floor plan may be drawn at 1:50 (1:48 or 1/4"=1'-0") whereas a detailed view may be drawn at 1:25 (1:24 or 1/2"=1'-0"). Site plans are often drawn at 1:200 or 1:100.

Showing dimensions

The required sizes of features are conveyed through use of dimensions. Distances may be indicated with either of two standardized forms of dimension: linear and ordinate.

• With linear dimensions, two parallel lines, called "extension lines," spaced at the distance between two features, are shown at each of the features. A line perpendicular to the extension lines, called a "dimension line," with arrows at its endpoints, is shown between, and terminating at, the extension lines. The distance is indicated numerically at the midpoint of the dimension line, either adjacent to it, or in a gap provided for it.
• With ordinate dimensions, one horizontal and one vertical extension line establish an origin for the entire view. The origin is identified with zeroes placed at the ends of these extension lines. Distances along the x- and y-axes to other features are specified using other extension lines, with the distances indicated numerically at their ends.

Sizes of circular features are indicated using either diametral or radial dimensions. Radial dimensions use an "R" followed by the value for the radius; Diametral dimensions use a circle with forward-leaning diagonal line through it, called the diameter symbol, followed by the value for the diameter. A radially-aligned line with arrowhead pointing to the circular feature, called a leader, is used in conjunction with both diametral and radial dimensions. All types of dimensions are typically composed of two parts: the nominal value, which is the "ideal" size of the feature, and the tolerance, which specifies the amount that the value may vary above and below the nominal.

• Geometric dimensioning and tolerancing Geometric dimensioning and tolerancing is a symbolic language used on engineering drawings and computer generated three-dimensional solid models for explicitly describing nominal geometry and its allowable variation is a method of specifying the functional geometry of an object.

Sizes of drawings

Main article: Paper size There have been many standard sizes of paper at different times and in different countries, but today there are two widespread systems in use: the international standard and the North American sizes

Sizes of drawings typically comply with either of two different standards, ISO The International Organization for Standardization , widely known as ISO (pronounced /ˈaɪsoʊ/ EYE-soe), is an international-standard-setting body composed of representatives from various national standards organizations. Founded on 23 February 1947, the organization promulgates worldwide proprietary industrial and commercial standards. It has (World Standard) or U.S. customary, according to the following tables:

ISO paper sizes

ISO A Drawing Sizes (mm)

A4	210 X 297
A3	297 X 420
A2	420 X 594
A1	594 X 841
A0	841 X 1189

U.S. Customary Drawing Sizes

A	8.5" X 11"
B	11" X 17"
C	17" X 22"
D	22" X 34"
E	34" X 44"

Other U.S. Drawing Sizes

D1	24" X 36"
E1	30" X 42"

The metric drawing sizes correspond to international paper sizes There have been many standard sizes of paper at different times and in different countries, but today there are two widespread systems in use: the international standard and the North American sizes. These developed further refinements in the second half of the twentieth century, when photocopying A photocopier is a machine that makes paper copies of documents and other visual images quickly and cheaply. Most current photocopiers use a technology called xerography, a dry process using heat. (Copiers can also use other output technologies such as ink jet, but xerography is standard for office copying.) became cheap. Engineering drawings could be readily doubled (or halved) in size and put on the next larger (or, respectively, smaller) size of paper with no waste of space. And the metric technical pens A technical pen is a specialized instrument used by an engineer, architect, or draftsperson to make lines of constant width for architectural, engineering, or technical drawings. It has been also generally called "rapidograph", although that particular name has officially remained a proper name for a line of products made by German were chosen in sizes so that one could add detail or drafting changes with a pen width changing by approximately a factor of the square root In mathematics, a square root of a number x is a number r such that r2 = x, or, in other words, a number r whose square is x of 2. A full set of pens would have the following nib sizes: 0.13, 0.18, 0.25, 0.35, 0.5, 0.7, 1.0, 1.5, and 2.0 mm. However, the International Organization for Standardization (ISO) called for four pen widths and set a colour code for each: 0.25 (white), 0.35 (yellow), 0.5 (brown), 0.7 (blue); these nibs produced lines that related to various text character heights and the ISO paper sizes.

All ISO paper sizes have the same aspect ratio, one to the square root of 2, meaning that a document designed for any given size can be enlarged or reduced to any other size and will fit perfectly. Given this ease of changing sizes, it is of course common to copy or print a given document on different sizes of paper, especially within a series, e.g. a drawing on A3 may be enlarged to A2 or reduced to A4.

The U.S. customary "A-size" corresponds to "letter" size, and "B-size" corresponds to "ledger" or "tabloid" size. There were also once British paper sizes, which went by names rather than alphanumeric designations.

American National Standards Institute The American National Standards Institute or ANSI [citation needed] is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organization also coordinates U.S. standards with international standards so that American (ANSI) Y14.2, Y14.3, and Y14.5 are standards that are commonly used in the U.S.

Technical lettering

Technical lettering Technical lettering is the process of forming letters, numerals, and other characters in technical drawing. It is used to describe, or provide detailed specifications for, an object. With the goals of legibility and uniformity, styles are standardized and lettering ability has little relationship to normal writing ability is the process of forming letters, numerals, and other characters In computer and machine-based telecommunications terminology, a character is a unit of information that roughly corresponds to a grapheme, grapheme-like unit, or symbol, such as in an alphabet or syllabary in the written form of a natural language in technical drawing. It is used to describe, or provide detailed specifications for, an object. With the goals of legibility and uniformity, styles are standardized and lettering ability has little relationship to normal writing ability. Engineering drawings use a Gothic sans-serif In typography, a sans-serif or sans serif typeface is one that does not have the small features called "serifs" at the end of strokes. The term comes from the Latin word "sine", via the French word sans, meaning "without" script, formed by a series of short strokes. Lower case letters are rare in most drawings of machines A machine is a device that uses energy to perform some activity. In common usage, the meaning is that of a device having parts that perform or assist in performing any type of work. A simple machine is a device that transforms the direction or magnitude of a force without consuming any energy. The word "machine" is derived from the Latin.

Example of an engineering drawing

Example mechanical drawing

Here is an example of an engineering drawing (an isometric view of the same object is shown above). The different line types are colored for clarity.

• Black = object line and hatching
• Red = hidden line
• Blue = center line of piece or opening
• Magenta = phantom line or cutting plane line

Sectional views are indicated by the direction of arrows, as in the example above.

See also

• Architectural drawing An architectural drawing or architect's drawing is a technical drawing of a building that falls within the definition of architecture. Architectural drawings are used by architects and others for a number of purposes: to develop a design idea into a coherent proposal, to communicate ideas and concepts, to convince clients of the merits of a design,
• CAD standards CAD Standards have been created to improve productivity and interchange of Computer-aided design documents between different offices and CAD programs, especially in architecture and engineering
• Computer-aided design Computer-aided design is the use of computer technology for the design of objects, real or virtual. CAD often involves more than just shapes. As in the manual drafting of technical and engineering drawings, the output of CAD often must convey also symbolic information such as materials, processes, dimensions, and tolerances, according to
• Descriptive geometry Descriptive geometry is the branch of geometry which allows the representation of three-dimensional objects in two dimensions, by using a specific set of procedures. The resulting techniques are important for engineering, architecture, design and in art. Drawing is the language of design, and if drawing can be thought of as a language then,
• Engineering drawing symbols
• Geometric tolerance Geometric dimensioning and tolerancing is a symbolic language used on engineering drawings and computer generated three-dimensional solid models for explicitly describing nominal geometry and its allowable variation
• ISO 128 ISO 128 is an international standard , about the general principles of presentation in technical drawings, more specific the graphical representation of objects on technical drawings Technical drawings – General principles of presentation
• Patent drawing A patent application or patent may contain drawings, also called patent drawings, illustrating the invention, some of its embodiments , or the prior art. The drawings may be required by the law to be in a particular form, and the requirements may vary depending on the jurisdiction
• Specification (technical standard) A specification is an explicit set of requirements to be satisfied by a material, product, or service. Should a material, product or service fail to meet one or more of the applicable specifications, it may be referred to as being out of specification; the abbreviation OOS may also be used
• Document management system

References

1. ^ Bertoline, Gary R. Introduction to Graphics Communications for Engineers (4th Ed.). New York, NY. 2009

This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be and removed. (September 2009)

Further reading

• Basant Agrawal and C M Agrawal (2008). Engineering Drawing. Tata McGraw Hill, New Delhi. [1]
• Paige Davis, Karen Renee Juneau (2000). Engineering Drawing
• David A. Madsen, Karen Schertz, (2001) Engineering Drawing & Design‎. Delmar Thomson Learning. [2]
• Cecil Howard Jensen, Jay D. Helsel, Donald D. Voisinet Computer-aided engineering drawing using AutoCAD.
• Warren Jacob Luzadder (1959). Fundamentals of engineering drawing for technical students and professional.
• M.A. Parker, F. Pickup (1990) Engineering Drawing with Worked Examples‎.
• Colin H. Simmons, Dennis E. Maguire Manual of engineering drawing. Elsevier.
• Cecil Howard Jensen (2001). Interpreting Engineering Drawings‎.

External links

Wikimedia Commons has media related to: Construction drawings

• Examples of cubes drawn in different projections
• Animated presentation of drawing systems used in technical drawing (Flash animation)

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