Brief history of technical & engineering drawings

Drawing is a universal language that human beings have been using to express the visual images they conceive in their minds; it is such an old practice that its recorded history could be as old as humanity.

There is evidence that as far back as 12,000 B.C., ancient caves were inscribed with drawings that give clues to some human experiences in prehistoric times.

Technical & engineering drawings—or drawings that communicate technical ideas—might have even existed before written language. There is evidence that what we now call “technical planning” in the present-day, actually started about 7,000 B.C.

As ancient and earlier societies became more civilized and advanced, they planned and organized how roads, cities, bridges and other structures would be built; technical drawing was the most important tool to achieve this goal, especially in the fields of engineering and architecture which are deeply ingrained in society.

At inception, technical drawings were drawn with hands by using tools that can be regarded as primitive versions of the present-day manual (traditional) technical & engineering drawing tools: set square, ruler, protractor and compass; it would remain this way for about 5,000 years before the beginning of engineering and architectural drawing/drafting.

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The earliest form of modern-day drawing instruments can be found in the Museum of the Louvre, Paris, on two headless statues of Gudea (2,130 B.C.).

In ancient times, Gudea was an engineer, and the governor of the city/state of Lagash which was located in the country later known as Babylon. Two contemporary drawing boards were also constructed and placed on the statues of Gudea.

The drawing boards had the top (plan) view of the temple of Ningirsu, and another drawing tool that looked like scribing instrument and scales.

The ancient Greek civilization has had a great deal of influence on modern-day drawing through its work in geometry. Many of the manual tools used in technical & engineering drawings, such as the compass and triangles, were developed when Greek civilization was at its peak.

Around the year 450 B.C., the architects of the Parthenon, Ictinus and Callicrates, used perspective drawing by foreshortening and converging parallel lines in their technical drawings.

At different points throughout history, great civilizations across the world (Africa, Europe, Asia, Middle East, South America, North America) adopted one form of technical drawing, or another.

Brief history of non-mathematical and mathematical approaches to technical & engineering drawings

During the renaissance (mainly between the 14th and 17th centuries), two popular approaches to drawing were developed at the time: the non-mathematical, and the mathematical approaches.

Giotto and Duccio used the non-mathematical approach to advance the applicability of perspective drawings by using symmetry, converging lines, and the technique of foreshortening.

On the other hand, Italian architect, Brunelleschi, used the mathematical approach and its terms to demonstrate the theoretical principles of perspective drawing. The era of Brunelleschi was followed by that of Alberti who mathematically defined the principles of perspective drawing in paintings.

Other people who advanced the mathematical approach were Francesca (who made 3-view drawings using orthogonal projection), Leonardo da Vinci (who wrote about the theory of perspective drawings), and Durer (who published a book on orthographic drawing). In the early 19th century, William Farish introduced isometric drawing as a type of pictorial drawing.

During the evolution of technical & engineering drawing, one thing is quite clear: in ancient times, it was difficult for human beings to express or illustrate 3D (three-dimensional) objects on 2D (two-dimensional) surfaces.

Brief history of the science of technical & engineering drawings known as “descriptive geometry

A young and exceptional mathematician named Gaspard Monge developed the science of technical drawing known as descriptive geometry while designing a complicated star-shaped fortress. He used orthographic drawing to solve some problems graphically, instead of mathematically.

The great contributions of Gaspard Monge are the basis of the today’s three-dimensional representations on two-dimensional media such a paper and computer screen.

Brief history of the computer graphics (CAD) form of technical & engineering drawings

Computers have had a significant impact on the types of projections used to design and produce technical & engineering drawings. In 1950, the first computer-driven display attached to MIT’s Whirlwind I computer was used to produce simple pictures; advances in computer graphics increased significantly since that time onwards.

An MIT graduate student named Ivan Sutherland published his doctoral thesis in 1963, and paved a way for the development of interactive computer graphics which later evolved into computer-aided design (CAD). In the middle of the 1960s, many studies were conducted in the field of computer graphics at MIT, Bell Telephone laboratories, GM, and Lockheed Aircraft.

Developments continued through the 1970s, and around 1980 IBM and Apple popularized the use of bitmap graphics which led to the widespread use of inexpensive graphic-based applications.

In the early 1980s computer-based software programs began to emerge, with AutoCAD and Versa CAD being the most popularly used at the time. From the 1990s till date, the world has witnessed the growth of CAD companies and 3D modelling which supports the design of objects, products and structures.

The importance of technical & engineering drawings

Technical & engineering drawing are real clear-cut languages used in the technical and engineering design processes for visualization, communication, and documentation; these are areas where technical & engineering drawing are very important.

As you may know, drawings are graphical representations of objects, shapes and structures that are drawn using either freehand, mechanical, or computer methods.

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Generally speaking, any technical or engineering drawing serves as a graphic model or representation of a real object or an idea that existed originally in the mind. Drawings could be abstract, such as the multi-view drawings shown in the figure below.

Figure 1_Multi-view drawing of a journal bearing

Figure 1: Multi-view drawing of a journal bearing which is actually a shaft or journal that rotates in a bearing

On the other hand, drawings could be more concrete, such as the computer model shown in the figure below.

Figure 2_A 3-D computer model of the inner part of an automobile

Figure 2: A 3-D computer model of the inner part of an automobile

Only knowledgeable and experienced practitioners of technical & engineering drawings can sufficiently interpret the types of lines, know the exact shapes of objects (rectangles, squares, circles, etc.) in figure 1, and have a clear mental picture of how objects would appear in three dimension (3D).

The 3-D computer model in figure 2 can be more easily interpreted and understood because its drawing or graphical details are expressed with different types of lights, colors, shades and shadows.

The projection techniques shown in figures 1 and 2 (in 2D and 3D; on paper and computer screens) took probably a hundred years or more to develop. Actually, it has taken millennia for the techniques of technical & engineering drawing to evolve into what we use today.

We will take a brief look at the importance of technical & engineering drawing in the following areas:

  • Visualization
  • Communication
  • Documentation

Technical & engineering drawings help in visualization, and problem solving

Technical & engineering drawing is a powerful tool that designers use to enhance their ability to develop greater ideas in the mind, and solve problems. As you may have known, visualization is the ability to produce mental pictures (in the mind) of things that either exist, or don’t exist.

Great designers like Leonardo da Vinci, and Jules Verne had excellent visualization skills that produced countless pictures of objects in their minds, and representations of how they would appear if they were/are moved around mentally—as if hands were used to move the objects around.

Everything in life—computers, cars, great pyramids, rockets, etc.—initially existed, not because of their shape or geometry, but because they were first thought about, pictured, or conceived in the minds of the people who finally constructed or produced them.

Most designers initially get ideas in the mind and sketch them on paper. Sometimes sketches are rough when initially drawn; at later stages sketches are refined with a more professional tone, and into more professional drawing.

Technical & engineering drawings make communication easy during design processes

Technical & engineering drawing is important because it aids communication and easy passage of ideas from one person to another, especially when it’s done without ambiguity and to such an extent that other people can be able to visualize and understand or interpret any design that embraces the basic components and code of practice of technical & engineering drawing.

Imagine how beautiful and clear final designs appear after technical drawing and 3D CAD modelling is used to clarify and refine sketches which were initially drawn as rough ideas from the mind.

Technical & engineering drawings help in documentation

Besides being useful in visualizing ideas and communicating effectively, technical & engineering drawing is important for documentation; and also for both legal and archival purposes. Documentation of drawings is always important for present and future needs so that anyone who comes across such drawing documents may benefit from it in one way or another.

Types of technical & engineering drawing lines and their uses

You can view pictorial illustrations of the most popular types of lines used in technical and engineering drawing by clicking here.

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The types and uses of various types of lines in technical & engineering drawing, are as follows:

Break lines

Break lines are used to create breakouts on sections in order to shorten distances between parts of a drawing, and give more clarity. Three types of lines are normally used as break lines; they have different line weights: long break lines, short break lines, cylindrical break lines.

Center Lines (or, long/short-dashed thin lines)

Center lines are used to locate or represent the centers of tools, circles, cylindrical surfaces or volumes, and symmetrical areas/objects, etc. Center lines are drawn as thin broken lines that have long and short dashes. In many instances, the long and short dashes vary in length; however, this depends on the scale or size of the drawing. Center lines could be extended and used as extension lines during dimensioning of objects or shapes.

Chain lines

Chain lines are broken or spaced parallel lines used to indicate either pitch lines (lines that show the pitch of gear teeth or sprocket teeth), center lines, developed views, or the features in front of a cutting plane. Usually, chain lines are applied at the beginning and end of long dashes, at center points as center lines, in dimensioning, or for other purposes.

Construction Lines

Construction lines (light thin lines) are used to develop shapes and locations of features in technical & engineering drawings. After using construction lines to develop thick visible outlines of objects, they are either left on the sketches of many drawings, or cleaned off with an eraser.

Continuous thick lines

Continuous thick lines are used to represent visible edges and outlines of objects, shapes, and structures on paper or computer. They are usually dark and heavy solid lines which are very prominent in many drawings.

Continuous thin lines

Continuous thin lines are used to represent dimension lines, extension lines, projection lines, hatching lines for cross sections, leader lines, reference lines, imaginary lines of intersections, and short center lines.

Cutting plane lines (viewing plane lines)

Cutting plane lines are used to indicate the positions of cutting planes in sections, or during sectioning. Two types of cutting plane lines can be used.

The first type is a dark line that consists of one long dash and two short dashes spaced alternately. Long dashes are usually drawn at any length between 20 and 40mm, or a little bit more; it depends on the scale and size of the drawing. On the other hand, short dashes are usually drawn approximately 3mm long, and spaced at 1.5mm (between dashes).

The second type of cutting plane line consists of short dashes of equal lengths, approximately 6mm long, with a space (of length) of 1.5mm between each short dash.

Dimension lines

Dimension lines are thin lines that have arrowheads at their opposite ends; they are used to show the precise length, breadth, width, and height of objects.

Extension lines

Extension lines are thin solid lines that are used to show the extent (beginning and end) of a dimension in a drawing. Extension lines are usually drawn at approximately 1.5mm away from the outlines of objects, and extended 3mm longer than the outermost arrowheads located at the ends of dimension lines.

Freehand Break lines (or continuous narrow irregular lines)

Freehand break lines are lines drawn with freehand, and used to indicate short-breaks or irregular boundaries; they can be used to set the limits of partial views or sections.

Hatching lines (or section lines)

Hatching or section lines are used to indicate the sectional view or outlook of surfaces produced as a result of making arbitrary cuts on an object. Hatching lines are usually thin lines that are drawn at angle 45°, and equally spaced.

Hidden Lines

Hidden lines are used to describe features that cannot be seen when objects are viewed from a particular direction; they consist of short and equally spaced thin dash lines and spaces. The dashes are usually three to four times longer than the space between them.

It is recommended that the dashes used in hidden lines should be approximately 3 mm long, and have a space of 1.0mm between each dash. On the other hand, the length of the dashes, and space between them can be slightly altered, depending on the scale and size of the drawing.

Leader lines

Leader lines are used to show the dimensions of an object, feature or structure whenever such dimensions are not clear enough after being placed beside objects, features, or drawn structures.

Long Break line (or continuous thin straight lines with zigzags)

Long break lines (or continuous straight lines with zigzags) show continuity of partially interrupted views; they are very suitable for computer aided design (CAD) drawings.

Symmetry Lines

Symmetry lines are imaginary lines that pass through the centers of areas, shapes, objects, and drawn structures; in most cases, symmetry lines divide objects into equal and similar-looking parts.

Visible Lines

Visible lines are thick and continuous bold lines that are used to indicate the visible edges of objects. They usually stand out when compared with other lines.

The figures below are pictorial views of various types of lines used in technical & engineering drawing:

Figure 1_drawing showing various types of lines

Figure 1: A drawing that shows various types of lines

Figure 2_drawing showing various types of lines

Figure 2: A drawing that shows various types of lines

Types of lines used in technical & engineering drawings

Technical and engineering drawings express precise requirements or specifications that should be easy to interpret. There are certain types of lines used for graphical communication in technical and engineering drawing in order to convey clear messages, and abide by good professional standards. Generally, most of the lines used in practice are of uniform thickness and density.

It is vital for drafters, designers, engineers, and people to understand how and when to apply the variety of line styles which serve as a reliable means of passing on valuable information when drawn and positioned properly on drawing paper or computer.

Most objects drawn in technical and engineering drawing practice are somewhat complicated and contain a lot of planes, surfaces and edges. In order to clearly distinguish many all of them, it is important to use technical and engineering drawing lines effectively.

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Lines make the difference; they are fundamental and perhaps the most important thing in technical and engineering drawings because they express or illustrate how shapes and sizes of objects would in real life after they are constructed.

In many cases, if every line has the same thickness, technical and engineering drawings would be confusing and difficult to interpret because some very important planes and parts of objects won’t stand out from dimension lines that describe only the outlook of objects.

By employing different types of lines on the basis of various thicknesses and designations, many features can be expressed in precise ways which would otherwise be difficult to express. To make sure everybody can interpret drawings the same way, the use of different types of lines was established decades ago by various committees that recognize the importance of standardization in technical & engineering drawing.

The most popular types of lines form the core of technical and engineering drawings. Some lines are dark, while others are light; some are thick, while others are thin; some are solid all through, while others are dashed in various ways.

The figures below illustrate the types of lines popularly used in technical and engineering drawing.

Figure 1_8 types of lines used in technical & engineering drawing.jpg

Figure 1: 8 types of lines used in technical & engineering drawing

Figure 2_4 extra types of lines used in technical & engineering drawing

Figure 2: 4 extra types of lines used in technical & engineering drawing

Figure 3_Other types of thin lines used in technical & engineering drawing

Figure 3: Other types of thin lines used in technical & engineering drawing

Figure 4_Hatching & cutting plane lines used in technical & engineering drawing

Figure 4: Hatching & cutting plane lines used in technical & engineering drawing

Figure 5_Example of technical & engineering drawing that uses 6 different types of lines

Figure 5: Example of a drawing that uses 6 different types of lines

The importance of standardization in technical & engineering drawings

Technical and engineering drawings/graphics are a bit more cumbersome or involving than artistic drawings because they require the use of terms, symbols and rules that are somewhat universal, and which knowledgeable people can understand and use in communicating.

Practitioners of both technical and engineering drawing have done a lot of work over decades to harmonize terms, symbols and rules universally, and in such a way that drawings made or produced in one city can be sent to another city, and understood by other people who can assembly the drawings and manufacture objects that were made or drawn somewhere else.

Standardization has made it possible to interpret one drawing in different parts of the world, no matter the language used; basically, drawings have only one interpretation. For well over 100+ years, a lot of countries set up committees on standardization in order to accomplish this goal.

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Basic Components of Engineering Graphics—the Code of Practice

Importance, and Uses/Applications of Engineering Graphics and Design

Usually, committees decide on very important factors such as the best methods that could give the clearest presentation of drawings, dimensioning, symbols, and allowances (tolerances)—amongst many others.

In addition, different line styles are considered, adopted, and used to represent visible or hidden lines, and also indicate the centers of different objects, shapes and features. If a single interpretation is desired globally, then the rules of standardization must be strictly adhered to, and correctly interpreted.

Committees from countries that are part of International Organization for Standardization (ISO)—the universal committee on standardization

Various countries have organizations, bodies or committees that have shaped how technical and engineering drawing is practiced. Just to name a few—the British Standards Institution (BSI), established in 1901, was the world’s first national standards body; in the United States, technical and engineering drawing standards are established by the American Society of Mechanical Engineers (ASME); while Canada has the Canadian Standards Association (CSA). Generally, across the globe there exist several other organizations or bodies; all of which we won’t be able to list in this article.

The British Standards Institution (BSI) has done a lot of work and published approximately 20,000 standards. Every year it issues around 2000 new and revised standards that cover new materials, emerging processes and technologies. In addition, it keeps the technical content of existing standards up-to-date.

Generally, members of organizations, bodies, and committees from many countries are part of the worldwide committee on standardization, which is popularly known as the International Organization for Standardization (ISO), and made up of national standards institutes from large and small countries which have different standards of living: basically, industrialized, or developed.

ISO develops technical standards that add immeasurable value to all types of businesses that use technical and engineering drawing; furthermore, it makes development, manufacturing and supply of services and products much more efficient and safe, and also makes trading easier and fairer between countries that don’t use a common language.

Although a lot of work has been done in the area of standardization, there are still certain areas of drawing practice that national standards have not yet been established for; for example, simplified drafting. In such a case, practitioners and authors have adopted certain practices used by leading industries, especially in the United States.

After the shape and size of any technical or engineering drawing is constructed, other important information for constructing the object is provided in such a way that it can be easily recognized by anyone who is knowledgeable or familiar with technical or engineering drawing.

A complete and comprehensive understanding of an object cannot be acquired by using only one pictorial view because many details of the object won’t be expressed, and may be hidden or not clearly shown if the object is viewed from only one side or direction. Because of this, any practitioner or drafter must express an object through a number of views of an object from different directions or axes. Views, such as top view, front view, and side view—either right or left—and so on, are employed in drawings in order to project one view from another, as shown in the figure below.

Figure 1_Orthographic views of an airplane

Orthographic views of an airplane

Application of standardization

Standardization has given a lot of uniformity to drawings, and has made it easier for people from different cultural background to make use of universally accepted and adopted ideas. That’s why designers have been urged to use stock standard lengths of screws wherever possible. Lengths of screws include: 3, 4, 5, 6, 8, 10, 12, 16, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, and 200 mm.

If the length of screw required is over 200 mm, then increments of 20 mm become the preferred ISO lengths. Sometimes this is necessary because not all diameters of screws are available for the lengths listed in the previous paragraph; for example, the lengths available for an M3 screw range between 5 and 35 mm; while the lengths available for an M10 screw range between 12 and 100 mm for a particular type of screw head. Different ranges do not always cover different types of screw heads—hence the recommendation to always check any stock lists used in technical and engineering drawing practice.

Common terms used to describe dimensions of objects/shapes used in technical & engineering drawings

The word “dimension” can be defined as the magnitude of a shape or object in a particular direction; it can also be defined as the linear measurement of a line used to describe the value of the length, breadth, height, thickness, or circumference of an object or structure. A dimension is one of the three coordinates of the position of a point, line, area or volume relative to three imaginary but real axes: x, y, and z.

The most common terms used to describe or express dimensions are height (or depth), length, breadth (or width); all three are often interchanged, with one dimension often being referred to by another name. The most important thing to take note of is the obvious fact each dimension or description refers to the orientation of an object along a particular axis; especially the x, y, and z axes, respectively.

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Many geometric shapes have two dimensions, while other types have three dimensions: width, depth, and height; or length, width, and height—whichever combination. The choice of terms used to describe the dimensions of an object depends on the orientation of the shape and size of the object.

Figure 1_140_3D object (cube) expressed in terms of height length and depth

Figure 1: A 3D object (cube) expressed in terms of height, length and depth. (Image credit: Curiositi.)

Figure 2_140_2D_3D rectangular objects expressed in terms of length_breadth and height

Figure 2: 2D and 3D rectangular objects expressed in terms of a combination of any 2 and 3 terms: length, breadth and height. (Image credit: Siyavula.)

There are quite a number of geometrical shapes used in technical and engineering drawing; they include: cones, cubes, cylinders, prisms, pyramids, spheres, toroids (doughnut-shaped objects), trapeziums, etc.

Whenever any two different shapes intersect/are used together, a kind of curve, interpenetration or intersection is employed to make sure they fit together. It is very important that students or practitioners be able to draw curves and intersections in order to make good drawings and communicate clearly using the different types of technical drawing.

Figure 3_140_Types or shapes of objects in 2D

Figure 3: Types or shapes of objects in 2D. (Image credit: Toppr.)

Figure 4_140_Types or shapes of objects in 3D

Figure 4: Types or shapes of objects in 3D. (Image credit: Toppr.)

Usually, a spherical-shaped object like a basketball is usually described as having a radius or diameter, which generally, is just one descriptive term—with the height of a basketball having the same dimension as the diameter.

Figure 5_140_Other types or shapes of objects in 3D

Figure 5: Other types or shapes of objects in 3D. (Image credit: http://www.mathcaptain.com.)

Usually, a cylindrical shape such as a baseball bat can be described by using terms such as “diameter”, and “length” or “height”—depending on whether it is standing up erect, or lying down flat. A hockey puck would be described using diameter, and width or thickness—i.e., two terms. On the other hand, objects that are not spherical or cylindrical could require three terms to appropriately describe their overall shape—as you might have noticed in Figure 1 (the first figure in this article).

The terms that would be used to describe a car, for instance, would include length, width, and height. Typically, width, height, and breadth would be used to describe a cupboard; while length, width, and thickness could be used to describe a sheet of drawing paper.

Generally, the terms used to describe the dimensions, sizes and shapes of objects are interchangeable, and usually done with respect to the position or orientation of objects when they are being viewed from a particular axis. For example, if a rectangular block is being viewed while it is lying flat on the ground (say, in 2D), it could be described as having a width and height; but if it is placed in a vertical standing position (say, in 3D), and viewed from the side, it could be described as having a height, width and breadth.

In order to avoid confusion, it is advisable that distances observed or taken from left to right be referred to as “width”; distances taken from front to back be referred to as “breadth”; while vertical distances taken from bottom to top (or vice versa) be referred to as “height”. Sometimes, the longest dimension of an object is referred to as the “length”.

In some other instances, there are certain unpopular shapes that are defined by applying mathematical methods; they include the type of complex shapes used in the design of structures such as automobiles, aircraft, and the hulls of ships—amongst many others.

Orthographic Drawing: Definition, Types, Views, Tutorial & Practice (PDF Download Available)

This article contains information about orthographic drawing (drafting or projection), and uses different images to illustrate the meaning and types of orthographic drawing. In addition, the article has 21 figures (images) of objects in 2D & 3D, and a tutorial on how to get started and going with orthographic drawing. The eBook/technical drawing PDF document of this article can be obtained by following an instruction at the end of this article. (Featured image credit: Pixabay.com.)

This article defines orthographic drawing (drafting or projection) and uses 21 images to illustrate the meaning and types of orthographic drawing. The eBook/technical drawing PDF document of this article can be gotten at the end of this article, along with a link to hundreds of images of two and three dimensional (2D & 3D) objects that can be used to practice and enhance orthographic drawing skills. Basically, both the article and eBook elaborate on the following:

  • Definition of orthographic drawing
  • Types of orthographic drawing
    • First angle projection
    • Third angle projection
  • Orthographic drawing views
  • Orthographic drawing tutorial & practice
    • Tools required for orthographic drawing practice
    • General procedure
    • Applications of orthographic drawing practice
    • Orthographic drawing shapes/objects for practice
  • Conclusion

If you are interested in downloading the eBook of this article, click here and download the eBook (PDF) for free. (Download Instructions: In order to download successfully, after you click the above link (or any of the links further below), also click the “Skip AD” button that will appear after a few seconds around the top right corner of your screen, and the file will appear for download. Alternatively, if the “Press allow” button appears, click it so that the file(s) will appear for download.)

Download PDF: Interpreting Engineering Drawings by Branoff, Theodore J.

Download PDF: Manual of Engineering Drawing by Simmons & Maguire

Download PDF: Technical Graphics Communication by Bertoline, Wiebe, Hartman & Ross

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All articles on technical drawing with engineering graphics

1. Definition of orthographic drawing

Orthographic drawing, which is one of the three types of parallel projections (orthographic, oblique, and axonometric), can be defined as a type of technical drawing in which 3-dimensional (3D) objects are represented in 2 dimensions (2D) by projecting planes (consisting of 2 major axes) of objects so that they are parallel with the plane of the media (paper, or computer) they are projected upon.

The two major types of orthographic drawing use two-dimensional views (obtained from different directions or lines of sight) to represent different parts of three-dimensional objects, or planes of objects viewed from/along different axes—typically, the x, y, and z axes.

Generally, the best way to fully express all of the most important visible parts of any 3D object in 2D views—in either first angle orthographic projection or third angle orthographic projection—is by using a maximum number of views, which in most cases is six.

However, in practice most people or organizations use three or four views to illustrate how shapes and sizes of various parts of an object look. Generally speaking, the number of views used in an orthographic drawing or projection depends on the purpose and objective of a drawing.

2. Types of orthographic drawing

Orthographic drawing (also known as orthographic projection) consists of two types: first angle projection, and third angle projection.

First angle projection

In first angle projection, which is popularly practiced in Europe, whenever six views are used to illustrate how the sides of a 3D object look from six directions (as shown in Figure 1 below), they are usually arranged in the following manner (as shown in Figure 2 below):

  • The bottom view E is placed at the top of the paper or computer screen.
  • The front view A is placed beneath the bottom view E.
  • The top view D is placed beneath front view A (i.e., at the bottom of the paper or computer screen.
  • The right view C is placed on the left side of front view A.
  • The left view B is placed on the right side of front view A.
  • The back/rear view F (which is not shown in Figure 2) is usually placed at the extreme left or right—whichever position is convenient.

Figure 1_six directions for six views

Figure 1: Six directions for six views. (Image Credit: Simmons, C. H. and Maguire, D. E. (2004). Manual of Engineering Drawing: p. 33.)

FIGURE~2

Figure 2: Five views of first angle projection; the sixth view F would depend on the shape of the back/rear view of the object. (Image Credit: Simmons, C. H. and Maguire, D. E. (2004). Manual of Engineering Drawing: p. 34.)

Whenever four views are used, the front view is usually placed at the top of a medium (paper, computer screen, etc.) along with the right side view which is placed at the left side of the front view, while the left side view is placed at the right side of the front view, and the top view (T) is placed alone beneath the front view.

It has to be noted that in many first angle orthographic drawing practices, three views could be sufficient enough to describe the shapes and dimensions of the most important sides of an object which actually exist in 3D as shown in Figure 3 below:

Figure 3_A three dimensional object with 7 visible edges

Figure 3: A three dimensional object with 7 visible edges

Third Angle Projection

In third angle projection, which is mostly practiced in North America, whenever six views are used to describe the sides of a 3D object from six different directions (as shown in Figure 1 above), they are usually arranged in the following manner (as shown in Figure 4 below):

  • The top view D is placed at the top of the paper or computer screen.
  • The front view A is placed beneath the top view D.
  • The bottom view E is placed beneath front view A (i.e., at the bottom of the paper or computer screen).
  • The right view C is placed on the right side of front view A.
  • The left view B is placed on the left side of front view A.
  • The back/rear view F (which is not shown in Figure 2) is usually placed at the extreme left or right—whichever position is convenient.

Figure 4_five views of 3rd angle ; a sixth View F would depend on shape of object

Figure 4: Five views of third angle projection; the sixth view F would depend on the shape of the back/rear view of the object. (Image Credit: Simmons, C. H. and Maguire, D. E. (2004). Manual of Engineering Drawing: p. 34.)

Whenever four views are used, the top view is usually placed alone at the top of a medium (paper, computer screen, etc.), while the front view is placed beneath the top view, and the right side view is placed at the right side of the front view, while the left side view is placed at the left side of the front view. (Note that third angle projection is the most popular type of orthographic drawing or projection.)

Generally, the difference between third angle projection and third angle projection depends on where each view is placed on paper or computer screen according to the universally accepted requirements of the two main types of orthographic drawing/projection.

3. Orthographic drawing views

There is no general rule per se, but the best or most recommendable way to fully express the most important visible planes/parts of any 3D object in 2D views, is by using as many views as possible: probably between three and six views.

Unlike in Figure 1 above, whenever six views are used, different directions (lines of sight projected on the sides of an object) can be chosen to illustrate the top, bottom, front, rear/back, left and right views, respectively, as can be seen in Figure 5 below:

Figure 5_six different directions and views

Figure 5: Six different directions (lines of sight) for six views. (Image credit: Google.)

The third angle projection of Figure 5 is shown in Figure 6 below:

Figure 6_third angle projection of object in Figure 5

Figure 6: Third angle projection of object in Figure 5. (Image credit: Google.)

The orthographic drawings or projections of other objects/shapes can be viewed in Figures 7, 8, and 9 below:

Figure 7_first angle projection of an object

Figure 7: First angle projection of an object: (Image credit: Google.)

Figure 8_Projection of object

Figure 8: Projection of an object. (Image credit: Google.)

Figure 9_Third angle projection of an that has dimensions in millimeters

Figure 9: Third angle projection of an object that has dimensions in millimeters. (Image credit: Google.)

Always remember that in many orthographic drawing practices across the world, the number of views chosen or used, usually depends on the number of views required or needed.

4. Orthographic Drawing Tutorial & Practice

Tools required for orthographic drawing practice

With regular drawing practice, it is very easy to learn and perfect orthographic drawing skills. The tools usually required for practicing orthographic drawing are quite the same as the ones specified in technical and engineering drawing, respectively. Generally, the tools include:

  • Drawing board.
  • Drawing paper: either Ao, A1, A2, A3, and A4.
  • Drawing pencil.
  • Eraser.
  • 30°×60° and 45°×45° set squares.
  • 300 mm (30 cm) ruler.
  • T-square.
  • Drawing compasses

Figure 10_Drawing board and drawing paperFigure 10: Drawing board and drawing paper

Figure 11 Complete set of drawing board, paper, set square, tsquare

Figure 11: A set consisting of a drawing board, drawing paper, tape/clips, set square for drawing vertical lines, and T-square for drawing horizontal lines. (Image Credit: The Hong Kong Polytechnic. (N.D). Fundamentals of Engineering Drawing & CAD: Engineering Drawing Lesson 1: p. 10.)

Figure 12_45 x 45 and 30 x 60 set squares

Figure 12: 45°×45° (bigger: on the left), and 30°×60° (smaller: on the right) set-squares

Figure 13_T squareFigure 13: T-square

Figure 14_Drawing compassesFigure 14: Drawing compasses (for drawing circular and elliptical shapes)

T-squares and set squares must be aligned perfectly on the pure/true x and y axes, respectively, before perfect vertical or horizontal lines can be produced. It will be difficult to produce good orthographic drawings without drawing or projecting perfect vertical and horizontal lines.

General Procedure

Generally, when projecting sides or different views of 3D objects in 2D, a certain degree of concentration will be needed to ensure that shapes, sizes or dimensions are consistent and accurate. The following are recommended when making orthographic projections:

  • Estimate the area of paper that would be enough to draw all necessary and important views. In addition, determine an appropriate scale for your drawings. A scale is any ratio (examples: 1:10, 1:100, 1:1000, etc.) of the size of an object on paper, to the actual size of the same object in real life. Common scales for “enlargement of objects” include: 3:1, 6:1, 10:1, etc. On the other hand, common scales for “reduction of objects” include: 1:3, 1:6, 1:10, etc.
  • Put equal distances (which should also be considered in the total area that would be enough to accommodate all views) between views; vertically (for the top, front, and bottom views), and horizontally (for the left, right, and back/rear views).
  • When drawing any view—whether square-, rectangular-, or circular-shaped—mark the center lines of each shape and the center/centroid of each shape. Center lines are very important, not just because they are center lines, but because they serve many other purposes, one of them being that they help in establishing other points and lines in drawings.
  • Draw the top view, and project the most visible and important lines into the front view, or vice versa.
  • After drawing the front view, the right and left side views can be projected and drawn. In addition, the bottom and back/rear view can be also be constructed if required.

Figure 15_Top view of an object drawn on drawing paper

Figure 15: Top view of an object drawn on drawing paper

As an example, in order to draw perfectly straight vertical and horizontal lines for the two dimensional (2D) top view ABCD of a 3D object on paper (as shown in Figure 15 above), the following steps should be taken:

  • Points and A and B should be the same distance away from the top border line on the drawing paper.
  • Points and C and D should be the same distance away from the bottom border line on the paper.
  • Points and A and C should be the same distance away from the left border line on the paper.
  • Points and B and D should be the same distance away from the right border line on the paper.

Applications of orthographic drawing practice

Orthographic drawings have many applications scattered across various fields that require planning and designing such as architecture, construction, design, engineering, environment, estate management, manufacturing, surveying, etc.

Orthographic drawings are usually produced according to precision and requirements. It is possible for an orthographic drawing that has been produced in one country, to be used to manufacture an object in another country.

Orthographic drawing shapes/objects for practice

Like we said earlier: “practice makes perfect”. In order to strengthen your orthographic drawing skills, you may practice how to draw the views of the following objects:

Figure 16_Third angle projection of object with six views

Figure 16: Third angle projection of object with six views. (Image credit: The Hong Kong Polytechnic. (N.D). Fundamentals of Engineering Drawing & CAD: Engineering Drawing Lesson 1: p. 32.)

Figure 17_3 commonly practiced orthographic views

Figure 17: Three commonly practiced orthographic views. (Image credit: The Hong Kong Polytechnic. (N.D). Fundamentals of Engineering Drawing & CAD: Engineering Drawing Lesson 1: p. 33.)

The three main 2D views, and six general 2D views of an L-shaped object can be seen in Figure 18 and 19, respectively.

Figure 18_three popular views

Figure 18: Three popular 2D views. (Image credit: Dr. Akhilesh Kumar Maurya. (N.D.). Orthographic Projections (ME 111): p. 13.)

Figure 19_Six views of the object in Figure 18 above

Figure 19: Six views of the object shown in Figure 18 above. (Image credit: Dr. Akhilesh Kumar Maurya. (N.D.). Orthographic Projections (ME 111): p. 15.)

The use of colors makes it easier to understand, locate, and draw 2D views of 3D objects. With the aid of colors on objects, you can study and practice how to draw Figures 20 and 21, respectively:

Figure 20_The use of colors in orthographic projection

Figure 20: The use of colors in orthographic projection. (Image credit: Dr. Akhilesh Kumar Maurya. (N.D.). Orthographic Projections (ME 111):p. 36.)

Figure 21_Three orthographic third angle projection views with colors

Figure 21: Three orthographic third angle projection views with colors. (Image credit: Dr. Akhilesh Kumar Maurya. (N.D.). Orthographic Projections (ME 111):p. 36.)

Conclusion

Anyone who is interested in succeeding with orthographic drawing or projection must practice consistently; there is no other easy or painless way out. The more one practices, the more proficient they will become in drawing and developing newer, sharper and more efficient ways to draw. Always remember that practice makes perfect; therefore, always practice.

In order to view and study various shapes/types of objects, click the following link: Hundreds of images of objects projected in 2 and 3 dimensions.

Basic Components of Engineering Graphics—the Code of Practice

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Basic Components of Engineering Graphics—the Code of Practice

Basic technical drawing is an essential component of all types of engineering graphics, nationally, and internationally. Within national and international trade, goods that are technical in nature almost always need to be accompanied by service diagrams or technical illustrations that express shapes, dimensions, and how components work whenever projections are assembled.

Examples of services could include consultancy work, design of a communication towers, installation procedure for technological inventions, or even instructions on how to assemble simple devices.

Whenever information is exchanged, especially between people who don’t understand/use a common verbal language, technical drawings can give clarity, even when language barriers exist.

Before a unified approach was ever agreed on, IS:696: “Code of practice for general engineering drawing” was originally issued in 1955, and revised twice in 1960 and 1972 respectively.

Growing international cooperation and exportation of technology has necessitated the development of an internationally unified format that consists of components, rules, codes, conventions and symbols that illustrate the language of technical drawing with engineering graphics.

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Since the publication of the code of practice, many countries have made a lot of progress in standardizing the components of technical drawing with engineering graphics because of their adherence to the mutual agreement on use of codes in and between countries.

The basic components of the code of practice used in technical drawing with engineering graphics include:

  • List of drawing tools and items.
  • Sizes/layout of drawing sheets.
  • Folding of drawing sheets: how to fold drawing sheets.
  • Assembly drawings.
  • 2-D and 3-D views.
  • Methods of dimensioning.
  • Methods of sectioning.
  • Cross-sectional views.
  • Half-sections.
  • Method for indicating surface texture.
  • General principles for dimensioning.
  • General principles of presentation: how to present drawings.
  • Linear and angular boundaries/tolerances for engineering and technical drawings.
  • Drawings for welding and metal work.
  • General scales used in drawing.
  • Lines: thicknesses, spacing, and proportional dimensions.
  • Lettering: dimensions and recommended sizes.

The eBook on “Technical Drawing with Engineering Graphics & Design in Practice: Definitions, Importance, and Applications”, which can be downloaded at the top of this page, discusses the following topics:

  • Definition of Engineering Graphics.
  • Definition of Graphical Engineering.
  • What Engineering Graphics and Design is all About
    • What is Engineering Design?
    • Application of Technical Drawing with Engineering Graphics in Engineering Design.
  • Basic Components of Engineering Graphics—Code of Practice.
  • Importance of Engineering Graphics and Design.
  • Uses/Applications of Engineering Graphics and Design.

Definition of Engineering Graphics, and Graphical Engineering

Importance, Uses/Applications of Engineering Graphics and Design

What Engineering Graphics and Design is all About

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Technical Drawing with Engineering Graphics & Design in Practice: Definitions, Importance, and Applications

This article defines technical drawing with engineering graphics in the context of design and practice. In addition, it provides detailed information about engineering graphics and design, and discusses the importance, basic components, and uses/applications of engineering graphics and design. (Featured image credit: Pixabay.com.)

Introduction

In the technologically advanced world of today, technical drawing with engineering graphics and design employs every important cognitive and manipulative skill in order to aid engineering graphical communication which uses lines, dimensions, scales, symbols and signs to illustrate how products, processes, services and systems look and work.

Technical drawing is applied in many fields, one of which is engineering graphics and design. Many students usually study technical drawing before gaining admission to read engineering and study engineering graphics which is just one out of many engineering subjects. The transition from technical drawing to engineering graphics and further study is usually much easier for students who have had past experience in technical drawing.

Although many people assume that technical drawing is the same as engineering graphics, there is actually a difference between the two: technical drawing is generally employed in producing diagrams and representations of object and shapes on paper, while engineering graphics is a technique used by engineers to produce engineering design drawings, including pictorial representations of data in computer-aided design (CAD) and manufacture with the use of softwares.

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Engineering graphics is somewhat an advanced type of technical drawing that clearly expresses the practical requirements for engineering forms or structures. Technical drawing goes hand in hand with engineering drafting graphics and design. Generally, whenever pencil and paper, or computer is used for drafting, it must be ensured that drafts are clear and visible enough to demonstrate how things work/would work.

The procedure, skill or actions often used to produce engineering graphics can be regarded as technical drawing or drafting. Note that technical drawing is also be applied in disciplines that are not usually regarded as fields of engineering; examples include landscaping, architecture, environmental health science, cabinet making, garment-making, etc.

Engineering graphics often combines many colors, various texts, and illustrations in order to communicate clearly and effectively using drawings, especially with people who understand the language of technical, or engineering drawing.

The complete eBook of this article can be obtained by following the links below and reading the contents. Basically, both the article and eBook discuss the following topics which can be read by following the links below:

    • What is Engineering Design?
    • Application of Technical Drawing with Engineering Graphics in Engineering Design.

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The above eBook discusses the following topics:

  • Definition of Engineering Graphics.
  • Definition of Graphical Engineering.
  • What Engineering Graphics and Design is all About
    • What is Engineering Design?
    • Application of Technical Drawing with Engineering Graphics in Engineering Design.
  • Basic Components of Engineering Graphics—the Code of Practice.
  • Importance of Engineering Graphics and Design.
  • Uses/Applications of Engineering Graphics and Design.

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Basic Components of Engineering Graphics—the Code of Practice

What Engineering Graphics and Design is all About

Importance, Uses/Applications of Engineering Graphics and Design

Definition & Types of Technical Drawing

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Importance, and Uses/Applications of Engineering Graphics and Design

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Importance of Engineering Graphics and Design

Just to mention a few, the importance of engineering graphics and design include (but are not limited to) the following:

  • Engineering graphics and design is important because it provides engineering and technology students with knowledge of techniques and standard practices generally employed worldwide in engineering graphics and design. This makes it easier or possible for design ideas to be adequately communicated, produced and used in many countries.
  • Engineering graphics and design is important because it sharpens the imagination, and helps engineering professionals solve more advanced technological problems related to engineering graphics and design.

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Uses/Applications of Engineering Graphics and Design

Although engineering graphics and design has many uses or applications, discussions will be limited to the following:

  • Engineering graphics and design can be used to produce “layout drawings” of completely designed end products; it can also be used in geometric studies to develop the movement of mechanical linkages, clearances, or arrangements.
  • Engineering graphics and design can be used to produce “mono-detail drawing” which is very important because it gives details and maximum clarity about any part of an engineering structure without having to view a whole structure.
  • Engineering graphics and design can be used to produce “assembly drawings” for 2-D projections that have to be joined together in order to form an “assembly” which gives clear and precise overview of structures.
  • Engineering graphics and design can be used to produce “installation drawings” in order to provide technical information on how to properly position and install items. Installation drawings could include dimensional data, hardware descriptions, and information regarding general configuration on installation sites where control systems, electrical systems, hydraulic systems, and other types of systems exist.
  • Engineering graphics and design can be used to produce “modification drawings” in order to alter characteristics of items that have been purchased in bulk; examples include hinges, extrusions, channel nuts, semi-processed items as electronic equipment drawers, castings, blank panels, castings, etc. Drafts for altered items are usually prepared whenever it becomes necessary to alter existing items.
  • Engineering graphics and design can be used to produce “procurement control drawings” which provide criteria on performance, and identification of supplier items that list the engineering design characteristics required to ensure control of interfaces, and repeatability of performance according to design. In the commercial realm of engineering practice, procurement control drawings can be prepared for item identification, purchased items, alteration to purchased items, selection from purchased items, and development/qualification of new items.
  • Engineering graphics and design can be used to produce “mechanical systematic diagrams” whenever general operating principles cannot be promptly determined after studying assembly drawings. Generally, mechanical schematic diagrams clearly illustrate design information for hydraulic or pneumatic systems, and complex mechanical systems such as the complex arrangement of gears, cams, linkages, clutches, linkages, etc.
  • Engineering graphics and design can be used to produce “electrical & electronic diagrams” (in accordance with ANSI Y14.15 or ANSI/IEEE STD 991) in order to clearly describe the elements and functions of electrical or electronic tools/equipment in accordance with ANSI/IEEE STD 91 and 315.

Engineering graphics and design can be used produce “functional block diagrams” in order to clearly illustrate the relationship between the functions of major elements in a system, or an assembly of various systems.

The eBook on “Technical Drawing with Engineering Graphics & Design in Practice: Definitions, Importance, and Applications”, which can be downloaded at the top of this page, discusses the following topics:

  • Definition of Engineering Graphics.
  • Definition of Graphical Engineering.
  • What Engineering Graphics and Design is all About
    • What is Engineering Design?
    • Application of Technical Drawing with Engineering Graphics in Engineering Design.
  • Basic Components of Engineering Graphics—the Code of Practice.
  • Importance of Engineering Graphics and Design.
  • Uses/Applications of Engineering Graphics and Design.

Definition of Engineering Graphics, and Graphical Engineering

Basic Components of Engineering Graphics—the Code of Practice

What Engineering Graphics and Design is all About

Definition & Types of Technical Drawing (PDF Download Available)

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What Engineering Graphics and Design is all About

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What Engineering Graphics and Design is all About

Engineering graphics and design is a combined creative activity aimed at producing engineering structures or outcomes that are useful to people and society. The graphic description of any engineering structure has to be clear and presentable, and in such a form that can be easily understood and constructed or built without much assistance from the designer.

What is Engineering Design?

Engineering design is the type of design practiced by engineers. Engineering design is different from planning because in planning—unlike in engineering design—expressions or presentations are not sufficiently complete or detailed enough to be built like final and complete designs can.

Application of scientific principles is the major thing that distinguishes engineering design from the type of design practiced by other professions: the major difference between engineering graphics and design, and the type of design practiced by other disciplines/professions is that, prior to construction, engineers use the principles of science to prove or demonstrate to an appreciable extent whether designs will work.

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With a great degree of accuracy, scientific principles can be used to predict the behavior of physical systems—this is where engineering design comes in. When applying engineering design, planned systems do not have to be real; however, they may have to be clearly and precisely described in mathematical terms.

In many fields of engineering, one of the most important goals of design is to ensure that all structures (bridges, buildings, automobiles, and aircraft) are capable of carrying loads and forces without failing or collapsing.

In order to determine whether a given bridge or building can withstand forces without failing, existing mathematical models have to be employed in making checks and assessments—this is design. Loads are expressed in mathematical terms, and relevant scientific principles (such as Newton’s laws and Hooke’s law) are used to estimate the stresses that would likely be produced in a structure whenever it is acted upon by various weights of loads or forces which could include human beings, chairs, tables, wind, etc.

By comparing the estimated stresses with the limiting values of the strengths of materials expected to be used, it can be determined whether or not any structure can perform certain functions. Engineering design is usually combined with engineering graphics in order to make important and precise descriptions for geometric and material properties of structures.

Without employing the principles of science, another way to determine whether a structure under design can perform its intended function, is to build it, test it, and hope for the best.

But in most cases, this is not a recommendable option because it doesn’t follow any tested and trusted guidelines like the fields of engineering do. Generally, the principles of science have an upper hand when it comes to design because they are based on past research and proven theories.

Before introducing technical drawing with engineering graphics into the scheme of planned construction, engineering designs have to be carefully validated (proven that they are in accord with important and applicable design criteria) in order ensure that the most important concerns have been addressed, and intended structures will perform their functions after being built or constructed in accordance with design.

Application of Technical Drawing with Engineering Graphics in Engineering Design

Technical drawing with engineering graphics has two major roles in practical engineering design processes:

  • To help communicate or pass on information in an easy and understandable way between participants of engineering design processes.
  • To help designers create better ideas when validating design outcomes or decisions.

It is important to note that in engineering practice, all graphics/drawings remain just a means to an end—successful construction and operation of structures. Generally, engineering graphics are created to serve and support design processes, which in turn assist in the construction of structures that serve greater purposes in society.

It is in this regard that engineering graphics is significantly different from artistic drawings that are created by artists. Unlike engineering drawing, the intention of most artistic drawings to create visually or aesthetically appealing effects.

In many cases, engineering designers do not build or construct their designs or works; for example, many engineering works are usually constructed or built by contractors who work independently of designers.

This implies that there is need to communicate effectively via drawings which can clearly and suitably describe what has been designed in order to be constructed or built. Due to the fact that engineering works are usually large and spacious, many objects are scaled down and graphically communicated in two- and three-dimensions respectively—i.e., in 2-D & 3-D.

Most times, the complete and final graphics of objects are issued at the end of engineering design processes, and provide complete descriptions of objects that would be constructed or built.

Engineering graphics can also be used to communicate internally within an organization that designs structures; for instance, communication can be from one designer to another, or from a designer to drafting staff.

Note

In order to effectively apply technical drawing with engineering graphics in any design process, engineers or students should be able to produce various types of drawing, formally, and informally. Generally, all drawings help the imagination to create and develop new ideas.

The eBook on “Technical Drawing with Engineering Graphics & Design in Practice: Definitions, Importance, and Applications”, which can be downloaded at the top of this page, discusses the following topics:

  • Definition of Engineering Graphics.
  • Definition of Graphical Engineering.
  • What Engineering Graphics and Design is all About
    • What is Engineering Design?
    • Application of Technical Drawing with Engineering Graphics in Engineering Design.
  • Basic Components of Engineering Graphics—the Code of Practice.
  • Importance of Engineering Graphics and Design.
  • Uses/Applications of Engineering Graphics and Design.

Definition of Engineering Graphics, and Graphical Engineering

Basic Components of Engineering Graphics—the Code of Practice

Importance, Uses/Applications of Engineering Graphics and Design

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Definition of Engineering Graphics, and Graphical Engineering

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Definition of Engineering Graphics

Engineering graphics can be defined as a graphical language that gives precise pictorial expressions of engineering structures, and is used to make communication possible between designers and other people who might not necessarily be engineering professional. Engineering graphics, which usually provides details that cannot be derived from engineering calculations, helps to convey ideas to people, and convert concepts into reality if drafts, illustrations or drawing follow universally accepted codes, criteria, and conventions.

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Definition of Graphical Engineering

Graphical engineering can be defined as the branch of engineering that deals with the study of computer-aided design (CAD) and imaging software aimed at creating digital sketches of engineering models, structures, plans, and projections for beneficial purposes. In addition, graphical engineering combines the knowledge of technical drawing with engineering graphics, and computer software and hardware to illustrate and manipulate engineering data/content for practical purposes.

It is quite common for graphical engineering students to study programming languages, 3-D maths, programming interfaces (API) used in building 3-D engines, rendering systems for 2-D and 3-D visuals, machine drawing & design, rapid prototyping, computer aided drafting, computer aided design (CAD), AutoCAD, 3-D modeling & parametric design, tooling drawing & design, industrial Management, etc.

The eBook on “Technical Drawing with Engineering Graphics & Design in Practice: Definitions, Importance, and Applications”, which can be downloaded at the top of this page, discusses the following topics:

  • Definition of Engineering Graphics.
  • Definition of Graphical Engineering.
  • What Engineering Graphics and Design is all About
    • What is Engineering Design?
    • Application of Technical Drawing with Engineering Graphics in Engineering Design.
  • Basic Components of Engineering Graphics—the Code of Practice.
  • Importance of Engineering Graphics and Design.
  • Uses/Applications of Engineering Graphics and Design.

Basic Components of Engineering Graphics—the Code of Practice

What Engineering Graphics and Design is all About

Importance, Uses/Applications of Engineering Graphics and Design

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Definition & types of technical drawing (PDF download available)

This article defines technical drawing (drafting or projection) and uses different images to illustrate the meaning, and types of technical drawing widely taught in schools and practiced in industries. The eBook/technical drawing PDF document of this article can be obtained at the end of this article. (Featured image credit: Pixabay.com)

This article defines technical drawing (drafting or projection) and uses different images to illustrate the meaning, and types of technical drawing widely taught in schools and practiced in industries. The eBook/technical drawing PDF document of this article is available to download for free. Although it contains all the information available in this article, it still has something extra on its last (17th) page: a link to hundreds of images of objects in 2 & 3 dimensions, and under different types of projections. Basically, both the article and eBook elaborate on the following:

  • Definition of technical drawing.
  • Types of technical drawing: parallel projection (orthographic—first angle, and third angle; oblique—cavalier, and cabinet; axonometric—isometric, dimetric, and trimetric), and perspective projection (1 point, 2 point, and 3 point).
  • Objectives of technical drawing.
  • Purpose of technical drawing.
  • Application of technical drawing.

If you are interested in downloading the eBook of this article, which also contains a link to hundreds of various shapes and sizes of objects in 2 & 3 dimensions, click here and download it for free. (Download Instructions: In order to download successfully, after you click the link above, or any of the links below, also click the “Skip AD” button that will appear after a few seconds around the top right corner of your screen, and the file will appear for download. Alternatively, if the “Press allow” button appears, click “allow” so that the file(s) will appear for download.)

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For further reading, you may download the best books on technical and engineering drawing by clicking the following links.

Download PDF: Technical Graphics Communication by Bertoline, Wiebe, Hartman & Ross

Download PDF: Interpreting Engineering Drawings by Branoff, Theodore J.

Download PDF: Manual of Engineering Drawing by Simmons & Maguire

1.0 Definition of technical drawing

Technical drawing can be defined as the graphic representation of an object, concept or idea using a universal language that consists of graphic symbols produced with the aid of drawing equipment/tools that can be used to measure straight and curved lines according to specified dimensions, scales, and codes of practice.

Technical drawing is used in many professions (engineering, architecture, manufacturing, construction, estate management, etc.) to draw or draft ideas and different views of physical objects like drainages, culverts, septic tanks, incinerators, houses, etc. Drawing—either artistic or technical—is one of the oldest forms of communication, and is believed to be older than verbal communication. Generally, there are two types of drawings: artistic drawing, and technical drawing:

Artistic Drawing

Artistic drawing is the type of drawing that is abstract because its meaning is unique to the person/artist who creates it. In order to understand the meaning of an artistic drawing, one has to understand the artist’s point of view or motivation for producing a specific artistic drawing.

Sometimes, it is necessary to understand an artist in order to understand their artistic drawing because artists often take a unique/abstract approach when communicating through their drawings. This type of approach gives rise to various interpretations when their drawings are exposed to public view.

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Regardless of how complex artistic drawings may appear, they express the clear feelings, beliefs, philosophies and ideas of the artists who create them. Artistic drawings are generally freehand drawings or drawings made without the use of drawing instruments/tools.

Technical Drawing

Technical drawing is the type of drawing that is not abstract because it doesn’t require an understanding of what its creator has in mind; rather, it requires an understanding that can only be gained by studying and using universally accepted tools, codes and conventions applicable to technical drawing.

In addition to the previously stated definition on technical drawing, we can say that technical drawing clearly, precisely and concisely communicates all important information conveyed by an idea produced in graphic form by the use of universally accepted codes of practice, tools, dimensions, notes, symbols, and specifications.

Technical drawing can be done manually, or with the use of computers. When any idea or object is drawn on computer, it is said to be drafted by computer aided design (CAD). One major advantage of using CAD is that revisions can be easily and speedily carried out on any draft.

Any student, architect, engineer, etc., must understand the theory behind projections, dimensioning, and conventions if they wish to become proficient in drafting and interpreting drafts. It is very important for people to understand manual (traditional) drawing/drafting before exposing themselves to CAD softwares. Why? Because an understanding of manual drawings would make it easier to use CAD.

2.0 Types of technical drawing

Technical drawings are constructed on the basis of fundamental principles of projection. There are two main types of technical drawing or projection: parallel projection, and perspective projection. (Note that each projection has various categories that will be illustrated further below.)

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A projection is any drawing, draft or representation of an idea or object that is carried out after considering views from various imaginary planes. Projections, which are quite similar to the direct views that one can see on televisions, can be used to represent actual objects if the following are employed:

  • the eye of the viewer looking at the object.
  • an imaginary plane of projection as dictated by the direction of the eye(s) of the viewer.
  • projectors or imaginary lines of sight.

The theories behind projection have been widely used to draft 3-dimensional objects on 2-dimensional media such as papers and computer screens. The theory of projection is based on two variables:

  • line of sight.
  • plane of projection: plane from which images can be projected—depending on the axis.
Figure 1: Lines of sight: parallel and perspective projections
Figure 1: Lines of sight: parallel, and perspective projections
Chapter 1_Figure_2_ planes of projection for parallel and perspective projectionssss.jpg
Figure 2: Planes of projection: parallel, and perspective projections

2.1   Parallel Projection

Parallel projection is the type of projection in which the lines of sight or projectors are parallel to each other, and also perpendicular to the planes of objects or images. Parallel projection can be categorized or divided into orthographic, oblique, and axonometric projections.

(1) Orthographic projection

Orthographic projection (or drawing) is the type of projection in which 3-dimensional objects are represented in 2 dimensions by projecting planes (consisting of 2 major axes) of objects so that they are parallel with the plane of the media they are projected on.

Orthographic projection can also be defined as the type of projection in which views are taken on different planes of objects and drawn (or represented) in 2 dimensions as illustrated by the principal views shown in the figures below:

Chapter 1_Figure_3_three major views of orthographic projection.jpg
Figure 3: Three major views in orthographic projection
Chapter 1_Figure_4_six general views of orthographic projection.jpg
Figure 4: Six general views in orthographic projection

There are two types of orthographic projection: first angle projection, and third angle projection:

In first angle projection (i.e., European/international system) the front view is placed at the top of a medium (paper, computer screen, etc.) along with the right side view which is placed at the left side of the front view, while the left side view is placed at the right side of the front view, and the plan (T) is placed alone beneath the front view.

In third angle projection (i.e., American system) the plan (T) is placed alone at the top, while the front view is placed beneath the plan, and the right side view is placed at the right side of the front view, while the left side view is placed at the left side of the front view. (Note that third angle projection is more popular than first angle projection.)

Chapter 1_Figure_5_first and third angle projections
Figure 5: First angle, and third angle projections

If you would like to read more details about orthographic projection or drawing, click here.

(2) Oblique projection

Oblique projection is the type of projection in which any object is drawn in 3 dimensions, with each of the 3 dimensions (or major planes) consisting of two lines (or major axes: either xy, or yz, or xz) perpendicular to each other (i.e. 90°), and one of the 3 planes parallel to the plane of paper, or computer screen, etc.

In addition, one of the 3 planes is projected at either 30°, 45° or 60° to the x axis. Oblique projection is of 2 types: cavalier, and cabinet projection.

Chapter 1_Figure_6_oblique_cavalier_cabinet projections.jpg
Figure 6: Oblique projection: cavalier, and cabinet projections

In cavalier projection, one of the 3 planes is drafted to represent a plane of an object “according to a given scale”, while in cabinet projection, one of the 3 planes is drafted to represent half of a plane of an object “according to half of a given scale”. A scale is any ratio (examples: 1:10, 1:100, 1:1000, etc.) of the size of an object on paper to the actual size of the same object in real life.

Chapter 1_Figure_7_oblique projection with orthographic views.jpg
Figure 7: Oblique projection with orthographic views

(3)   Axonometric Projection

Axonometric projection is the type of projection that consists of three-dimensional drawings in which each of the 3 major axes (x, y, and z) of an object is drawn perpendicular to each other by either 30°, 45°, or 60°, and no plane of the object is drawn parallel to the plane of media—paper, computer screen, etc. Axonometric projection/drawing can be categorized into three types: isometric, dimetric, and trimetric projections.

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Isometric projection is a method of projection/drawing in which the edges of 3-dimensional objects are represented by 3 axes perpendicular to each other and inclined to each other by 120° on the plane of media—paper or computer; also, 2 of the 3 axes are inclined at either 30°, 45°, or 60° to any imaginary x axis on any media.

In dimetric projection, 2 angles between any 2 major axes are unequal, while in trimetric projection, the 3 angles between the 3 major axes are unequal. Two different angles are required to construct 2 planes of objects in dimetric projections, while 3 different angles are required to construct 3 planes of objects in trimetric projections.

Chapter 1_Figure_8_Axonometric projection_Isometric_dimetric_trimetric
Figure 8: Isometric, dimetric, and trimetric projections

2.2   Perspective Projection

Perspective projection is the type of projection in which objects appear smaller as their distances from an observer increases: objects dimensions along a line of sight appear shorter than they actually are.

There are 3 types of perspective projections: 1 point, 2 point, and 3 point projections. One point perspective projections consists of 1 vanishing point, while 2 point and 3 point perspective projections consist of 2 and 3 vanishing points, respectively.

A vanishing point is a point of convergence where all lines of sight meet.

Chapter 1_Figure_9_one point perspective projection
Figure 9: One point perspective projection
Chapter 1_Figure_10_two point perspective projection
Figure 10: Two point perspective projection
Chapter 1_Figure_11_three point perspective projection
Figure 11: Three point perspective projection

3.0 Objectives of technical drawing

The general objectives of studying technical drawing include the following:

  • to develop skills in using universally accepted tools, symbols, scales and conventions to draw any visible object or invisible idea on paper, and computer.
  • to understand orthographic and isometric projections and employ it in drafting/drawing ideas and objects using both projections, respectively.
  • to understand and interpret technical drawings, sketches, and working drawings.
  • to develop the ability to use imagination to observe, visualize and draft objects, ideas or concepts.
  • to develop the ability to produce clean, accurate, neat, and informative drawings in a moderate amount of time.
  • to develop the ability to take on any projects and draw environmental health science, civil and environmental engineering objects/structures.

4.0 Purpose of technical drawing

To draft and design objects or structures, and assess how they would appear in real life after they are manufactured, fabricated, assembled, constructed or built. For example, houses, septic tanks, drainages, etc., must be designed and assessed before they are built.

5.0 Application of technical drawing

Technical drawings have wide applications in any field in which planning and designing are required, such as architecture, manufacturing, engineering, construction, environment, estate management, etc.

Sanitarians, surveyors, environmental scientists, and civil/environmental engineers use technical drawings to supervise construction of layouts, structures, objects, and boundaries for various types of properties (houses, etc.).

Technical drawings are also used in situations where ideas/designs for objects and structures need to be modified, and different 2-dimensional views need to be assembled into 3-dimensional views.

Generally, technical drawings are used by a variety of professions, including but not limited to:

  • engineers.
  • architects.
  • contractors.
  • inventors.
  • technicians.
  • teachers.
  • etc.

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