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Orthographic projection. Projections of points. Projection of straight lines. Projections of auxiliary planes. Projections of planes. Projections of Solids. Sections of solids. Development of surfaces. Intersection of surfaces. Isometric projection. Oblique projection. Perspective projections. Orthographic reading and conversion of views. What is its meaning? On a map of Bangladesh you measured the distance from Dinajpur to Dhaka as 6 inch.

Actually the distance is miles. What should be the possible R. A 15 cm scale measures a maximum length of 10 km. What is its R. If 9 hectares of area is represented by 1mm2 in a map, what is the value of R. During the construction of scale why the zero notation placed at 2nd division? How can you divide a 1mm line in 7 equal parts?

To provide necessary information about an object to the manufacturer or to any other concerned party, it is usual practice to provide projection s of that object.

If straight lines rays are drawn from various points on the contour of the object to meet a transparent plane, thus the object is said to be projected on that plane. The figure or view formed by joining, in correct sequence, the points at which these lines meet the plane is called the projection of the object. Pictorial Projection 3. Perspective Projection 7. When the projectors are perpendicular to the plane on which the projection is obtained, it is known as orthographic projection.

Following six views are possible in orthographic projection of a solid object. Top View b. Front view c. Left View d. Right View e. Rear view f. Bottom view Fig. They have the advantage of conveying an immediate impression of the general shape and details of the object, but not its true dimensions or sizes. Pictorial projections may be of two types as a.

Axonometric b. Oblique 7. Axonometric projections are classified according to how the principle axes are oriented relative to the projected surface. There may be three types as: i. Isometric ii. Dimetric iii. Trimetric Fig. The angle is usually kept This may be of two types: i. Cavalier Projection: In this case, the dimensions along all the axes are plotted in full scale. Cabinet Projection: In this case, the dimensions along the diagonal axis are plotted by reducing it to half of the actual value.

Dimensions along other axes are plotted in full scale. In case of perspective projection observer is considered to be at finite distance where in case of any other type of projection observer is considered to be at infinity. In short, orthographic projection is the method of representing the exact shape of an object by dropping perpendiculars from two or more sides of the object to planes, generally at right angles to each other; collectively, the views on these planes describe the object completely.

Descriptive geometry is basically the use of orthographic projection in order to solve for advanced technical data involving the spatial relationship of points, lines, planes, and solid shapes. The most common means of understanding these types of orthographic projection is – The Glass Box method. It can be suitably used for understanding the generation of orthographic views.

The box is unfolded to obtain the arrangement of views. In figure 7. The line of sight is always perpendicular to the plane of projection, represented by the surfaces of the glass box top, front, and right side. Projection lines C connect the same point on the plane of projection from view to view, always at right angle.

A point is projected up on the plane of projection where its projector cuts that image plane. In the figure 7. When it intersects the horizontal plane top plane of projection , it is identified as 1H, when it intersects the frontal plane front plane of projection , it is identified as 1F, and where it intersects the profile plane right side plane of projection , it is labeled 1P.

On these planes, views of the object can be obtained as is seen from the top, front, right side, left side, bottom and rear. Consider the object and its projection in fig. In actual work, there is rarely an occasion when all six principal views are needed on one drawing. All these views are principal views.

Each of the six views shows two of the three dimensions of height, width and depth. In general, when the glass box is opened, its six sides are revolved outward so that they lie in the plane of the paper.

And each image plane is perpendicular to its adjacent image plane and parallel to the image plane across from it. Before it is revolved around its hinged fold line reference line. A fold line is the line of intersection between any hinged adjacent image planes. The left side, front, right side, and back are all elevation views. Each is vertical. The top and bottom planes are in the horizontal plane. But in most cases the top, front, and right sides are required.

Sometimes the left- side view helps to describe an object more clearly than the light side view. Orthographic views are arranged in two techniques as a. First Quadrant Fig. When an inclined or oblique line is to be projected it is helpful to identify and draw the end points and then joining them to obtain the projection.

Parallel Inclined Fig. Oblique Fig. The edges, intersections, and surface limits of these hidden parts are indicated by a discontinuous line called a dashed line or hidden line.

Particular attention should be paid to the execution of these dashed lines. If carelessly drawn, they ruin the appearance of a drawing. All the center lines are the axes of symmetry. Hidden portions of the object may project to coincide with visible portions. Center lines may occur where there is a visible or hidden out line of some part of the object. Since the physical features of the object must be represented full and dashed lines take precedence over all other lines since visible out line is more prominent by space position, full lines take precedence over dashed lines.

A full line could cover a dashed line, but a dashed line could not cover a full line. When any two lines coincide, the one that is more important to the readability of the drawing takes precedent over the other.

The following line gives the order of precedence of lines. Full line 2. Dashed line 3. Careful line or cutting — plane line 4. Break lines 5. Dimension and extension lines. Crosshatch lines.

The points which are connected by lines in original object should be connected in the vertical plane. All other 5 views can be obtained in similar way. The plane of projection vertical, in case of front view should be parallel to the face for which views are being drawn.

For example, in case of top view the plane will be horizontal. In the projection there is a relationship of different views. It is usual practice to draw the front view first, then top and side views are drawn with the help of the vertical and horizontal projection lines.

This can be done using T-square, set-squares and compasses. Here only the figure C requires the use of compass in addition to T-squares and set- squares. The spacing between views has to be determined or decided beforehand and if equal spacing is needed then fig.

A can be followed and if a different spacing is needed then fig. B can be followed. Sufficient space should be provided in order to give dimensions avoiding any crowding and also excessive space should be avoided.

If not mentioned or required otherwise 30mmmm spacing can be provided between two successive views. Position of this line depends on the spacing requirement between side view and front view. If equal spacing is required then the line should originate at the corner of the front view. These lines will cut the diagonal line.

It is to be noted that for 1st angle projection the lines should be projected according to position of views. For example to draw top view, vertically downward lines need to be projected from front view so that the top view is generated below the front views; for getting right side view horizontal lines from front view are to be projected toward left and so on.

The length along the third axis cannot be shown in same view. This makes it difficult to understand them and only technically trained persons can understand the meaning of these orthographic views. A layman cannot imagine the shape of the object from orthographic projections. To make the shape of an object easy to understand for both technical persons and non-technical laymen pictorial projections are used. Most commonly used pictorial drawing is Isometric drawing. When a drawing is prepared with an isometric scale or otherwise if the object is actually projected on a plane of projection, it is an isometric projection.

For this purpose the object is so placed that its principle axes are equally inclined to the plane of projection. In other words, the front view of a cube, resting on one of its corners is the isometric projection of the cube as shown in fig.

But as the object is tilted all the lengths projected on the plane appears to be shortened and thus they are drawn shortened in isometric projection. In the isometric projection of a cube shown in Fig. The extent of reduction of an isometric line can be easily found by construction of a diagram called isometric scale. For this, reproduce the triangle DPA as shown in Fig.

Mark the divisions of true length on DP. Through these divisions draw vertical lines to get the corresponding points on DA. The divisions of the line DA give dimensions to isometric scale. The lines that are parallel on the object are parallel in the isometric projection. Vertical lines on the object appear vertical in the isometric projection. A line which is not parallel to any isometric axis is called non-isometric line and the extent of fore- shortening of non-isometric lines is different if their inclinations with the vertical planes are different.

Drawing of objects is seldom drawn in true isometric projections, as the use of an isometric scale is inconvenient. Instead, a convenient method in which the foreshortening of lengths is ignored and actual or true lengths are used to obtain the projections, is applied which is called isometric drawing or isometric view.

This is advantageous because the measurement may be made directly from a drawing. The isometric drawing is An isometric drawing is so much easier to execute and, for all practical purposes, is just as satisfactory as the isometric projection. Box method. Off-set method. In this method, the object is imagined to be enclosed in a rectangular box and both isometric and non-isometric lines are located by their respective points of contact with the surfaces and edges of the box.

It is always helpful to draw or imagine the orthographic views first and then proceed for isometric drawing. In the off-set method, the curved feature may be obtained by plotting the points on the curve, located by the measurements along isometric lines.

If there are some inclined lines in the plane it will be helpful to enclose the plane with a rectangle and then obtain the projection with reference to the sides of that rectangle. ABCD is the required isometric projection. This can also be drawn as shown in Fig. Arrows show the direction of viewing. Arrow at the top shows the direction of viewing.

Similarly the fig. The line 3-A will intersect the line at point M. Similarly obtain the intersecting point N. With center 3 and radius 3-D draw an arc AD. Similarly the isometric views can be obtained on vertical planes as shown in fig. Then the isometric box is constructed and the orthographic views are reproduced on the respective faces of the box.

Finally by joining the points relating to the object and erasing unnecessary lines the isometric view is obtained. In a specific isometric drawing three maximum faces can be shown. Usually front view, top view and either left or right side view are selected.

Use set square to make angles. Remember to cut height along vertical isometric axis. To do this, draw 2 parallel lines of each isometric axis at the end points of other two axes. Erase the non- existing lines.

Compare the orthographic views with your obtained Isometric views. If not, you are done. Step-1 b Step-2 Step-3 c d Step-4 e Fig. Draw isometric view from the orthographic views given in figures below: Md. Draw isometric view of a hexagonal prism 30mm sides and 60mm height. Solution: Draw the orthographic views first. Following section 7. For projecting the hexagonal top view on the top face of isometric box follow section 7. Draw isometric view of a cone with base diameter 30mm and axis 50 mm long.

For projecting the circular top view on the top face of isometric box follow section 7. Exercise and Assignments: 1. Draw orthographic views of the following objects wooden objects available : 1 2 3 4 Md.

Draw orthographic views for the following pictorial views Assume arbitrary dimension : 1 2 3 4 Md. Draw necessary orthographic views to represent i.

A reading table ii. Sitting chair iii. Twin seats of university bus. Laptop computer v. Wall clock. D-box of HSTU. A pentagonal pyramid.

A Cylindrical pen holder. An oval shaped paper-weight. Draw isometric view of a rectangular plane having length of sides as 10 cm and 15 cm when its plane is a horizontal and b vertical. Draw isometric view of a square prism with a side of base 5cm and axis 15 cm long when the axis is a vertical and b horizontal. Draw isometric view of a cylinder with base diameter 10cm and axis 15 cm long. A pentagonal pyramid of side of base 30mm and height 70mm is resting with its base on horizontal plane.

Draw the isometric drawing of the pyramid. Draw isometric views of i. Prepare isometric drawing from the given orthographic views. Use assumed value for missing dimensions 2 1 3 4 5 6 Md. Why have you studied projection? Define projection. Why it is necessary? What do you mean by projection plane, projector and view?

Show in a sketch. Classify projection and define the types. What are the possible orthographic views of an object? Are all the orthographic views necessary to describe an object?

If not, how will you choose the necessary views? Describe the glass box method. What do you mean by 1st angle and 3rd angle projection? Which one is British and which one is American System? Which one is easier and why? Differentiate between 1st angle and 3rd angle projection. Show the arrangement of views in 1st and 3rd angle projection system. Which lines are projected to their actual length? Which lines are not projected to their actual length?

How will you obtain projection of such lines? How do you represent a hidden edge in a particular view? How do you represent a hole in orthographic view?

What is the order of precedence of line in orthographic projection? What will you do, if a solid line and a hidden line occur at the same location?

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Welcome to EasyEngineering, One of the trusted educational blog. Check your Email after Joining and Confirm your mail id to get updates alerts. Other Useful Links. Your Comments About This Post. Is our service is satisfied, Anything want to say? Cancel reply. Engineering drawing is a two dimensional representation of three dimensional objects.

In general, it provides necessary information about the shape, size, surface quality, material, manufacturing process, etc.

It is the graphic language from which a trained person can visualize objects. Drawings prepared in one country may be utilized in any other country irrespective of the language spoken. Hence, engineering drawing is called the universal language of engineers. Any language to be communicative should follow certain rules so that it conveys the same meaning to everyone. Download Book.

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Textbook of Engineering Drawing Pdf Download » Dev Library.(PDF) Engineering Drawing for Beginners | Md. Roknuzzaman – replace.me

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Sign up for free Log in. EMBED for wordpress. Fourth edition of the book is enlarged to cover the syllabi of all universities. It is structured to cover the principles and practices as recommended in BIS: SP Salient Features – BIS standards are followed throughout the book in first angle projection as recommended and uniform aligned system of dimensioning. This enables the student and staff to understand the subject with ease and enthusiasm by self study. Special care is taken to explain this in 4 stages of drawing for easy understanding.

The subject ‘Technical Drawing’ has been introduced in the 1st semester of all branches in state polytechnics under the West Bengal State Council of Technical Education with modifications as per model syllabus issued by the All India Council for Technical Education with effect from session.

It covers all the features of the entire syllabus of ‘Technical Drawing’. For all students and lecturers of basic engineering and technical drawing The new edition of this successful text describes all the geometric instructions and engineering drawing information, likely to be needed by anyone preparing or interpreting drawings or designs.

There are also plenty of exercises to practise these principles. Skip to content. A Text Book of Engineering Drawing. Author : R. Dhawan Publsiher : S. A Textbook of Engineering Drawing. Author : Shah P.