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The primary objective of this book is to provide an easy approach to the basic principles of Engineering Drawing, which is one of the core subjects for undergraduate students in all branches of engineering. Further, it offers comprehensive coverage of topics required for a first course in this subject, based on the author’s years of experience in teaching this subject.

Emphasis is placed on the precise and logical presentation of the concepts and principles that are essential to understanding the subject. The methods presented help students to grasp the fundamentals more easily. In addition, the book highlights essential problem-solving strategies and features both solved examples and multiple-choice questions to test their comprehension.

### Chapter 1. Introduction

The successful teaching of any engineering subject rests 49% with the students and 51% with the teacher. This is true in subjects like ‘Engineering Drawing’ wherein the student is learning the skill to communicate his ideas through drawings since the beginning of the class. It is our universal language even today when some our drawings are prepared by computers and plotters. Hence, we need not overemphasize the fact that engineering student must be proficient in ‘Engineering Drawing’ for a full and complete exchange of ideas with colleagues.
K. Rathnam

### Chapter 2. Geometrical Construction

An attempt is made to provide in this chapter few carefully planned problems in practical geometry. An oppotunity is offered to review the fundamental principles of geometry without the mathematical proofs. The geometrical constructions detailed utilize time-saving methods by the use of drawing instruments.
K. Rathnam

### Chapter 3. Scales

Drawings of buildings/machines are prepared adopting a scale, and the scale adopted is to be mentioned below the drawing. If a drawing is made of the same size as the object, the view obtained will have the same size as the object. The drawing thus obtained is called a full size drawing and the scale used is called full size scale. If the object is larger in size, its drawing cannot be accommodated in the standard size drawing sheets. Hence, the drawing is made smaller in size. The scale used for this type is called a reduced scale. Objects of smaller sizes require drawings of larger in size. The scale used for drawing such components is called an enlarged scale. A scale is used to prepare a reduced or an enlarged size drawing.
K. Rathnam

K. Rathnam

### Chapter 5. Orthographic Projections

An engineer must be able to visualize in his mind how an object looks like without actually having the object. He must also be able to describe the object so that others could build it from the information provided on his drawing. The description of an object with lines requires a thorough knowledge of the principles of orthographic projections.
K. Rathnam

### Chapter 6. Projections of Points

In orthographic projection, an exact view of an object is obtained on a plane by projectors drawn from the end points of the object to meet the plane of projection at right angles. The view obtained in general consists of line representing edge of the object and lines representing surfaces of the object. A line on the view is obtained by the projections of two end points of the edge. Hence, the projection of points shall be the starting point to understand the theory of projection of lines and surfaces of the object. As the point has no dimension, its location is specified with reference to the co-ordinate planes. The point can be located in any of the four quadrants.
K. Rathnam

### Chapter 7. Projections of Lines

The projections of a straight line in various positions in the first quadrant are grouped based on its orientation with reference to the vertical and horizontal planes. They are:
1.
Parallel to both the planes

2.
Perpendicular to one plane

3.
Parallel to one plane and inclined to the other plane

4.
Lying in one plane

5.
Lying in the reference line xy (intersection of the VP and the HP)

6.
Inclined to both the planes

7.
Inclined to both the planes with an end in the reference line xy

8.
Inclined to both the planes with ends in both the planes

9.
Perpendicular to the reference line xy

K. Rathnam

### Chapter 8. Projections of Plane Figures

A plane surface enclosed or bounded by straight lines or a curved line is called a plane figure. The least number of straight lines which can enclose a space is three. When three straight lines intersect, the plane surface enclosed is a triangle. With four straight lines, the figure obtained is a quadrilateral. The most common plane figures are set squares (30°–60° and 45°). Other common plane figures include square, rectangle, pentagon, hexagon, octagon, circle, ellipse, etc.
K. Rathnam

### Chapter 9. Projections of Solids

A solid may be defined as an object having dimensions like length, breadth and thickness. Solids generally used in the study of Engineering Drawing may be classified as:
1.
Polyhedra

2.
Solids of revolution.

K. Rathnam

### Chapter 10. Auxiliary Projections

The projections of an object when its base is inclined to one of the principal planes (HP/VP) are difficult to obtain in one step. Hence, the object is kept initially in simple position to get its projections. Thereafter, the position of the object is changed to satisfy the given condition with reference to one of the principal planes (VP or HP) to which its base/axis is inclined. In this method, the angular points of the object move parallel to the other principal plane (HP or VP). One of the principal views (plan or elevation) will be common to the other two views. The common view and the latest view obtained complete the projections of the object. This method of projection is called change of position method. In the other method, an auxiliary plane is chosen to satisfy the given condition instead of changing the position of the object. The projection on the auxiliary plane furnishes the solution of the problem.
K. Rathnam

### Chapter 11. Sections of Solids

The working parts of a machine are generally made of a number of geometric shapes assembled to produce the desired form. The details of such parts are hidden in an outside view of the machine. The machine is assumed to be cut through by a section plane. Sectional views are obtained to show the true forms of hidden or internal parts. In solid geometry, the solid is cut through by a section plane. The portion of the solid between the section plane and the observer is removed. If the portion of solid between the section plane and the plane of projection is projected, as well as the section, the projection is called a sectional plan or sectional elevation. The true shape of the section is obtained in sectional plan if the section plane is parallel to the horizontal plane. The sectional elevation shows the true shape of the section if the section plane is parallel to the vertical plane. If the section plane is not parallel to any one of the principal planes, an auxiliary projection is necessary on a plane parallel to the section plane to show the true shape of section. The projection of section is distinguished by drawing evenly spaced thin lines, called section lines, drawn at 45° to the horizontal or the reference line xy.
K. Rathnam

### Chapter 12. Intersection of Surfaces

The need to determine the lines or curves of intersections between two surfaces of similar or different geometric shapes occurs in the fabrication of ducts, boiler mountings, pipe fittings, aircraft and automobile bodies. If two geometric shapes with curved surfaces meet or penetrate each other, the lines of intersection is a curve. The curve of intersection is determined by plotting the projections of points which are common to both surfaces. This is done by choosing section planes which cut the surfaces in lines or circles. The intersections of these lines give points on the required curve.
K. Rathnam

### Chapter 13. Development of Surfaces

The development of a three-dimensional object made of thick paper or sheet metal is a plane figure obtained by unfolding the surface of the object onto a plane. The development consists of drawing successive surfaces of the object in its true size. As there is no stretching of the surface in the development, every line on the development shows the true length of the corresponding line on the surface. Polyhedrons and single-curved surfaces (cylinder and cone) are developable. Double-curved surfaces cannot be developed to their true sizes, because these surfaces contain no straight lines.
K. Rathnam

### Chapter 14. Isometric Projections

It is easy to draw the two principal views (plan and elevation) of an object from its pictorial representation. The reverse is not always easy to visualize the object from two of its principal views. A third view on the profile plane aids to visualize the exact shape of the object. Isometric projection is an orthographic projection of an object on the vertical plane showing its three dimensions in one view (elevation). To understand the principles of isometric projection, let us consider the auxiliary projection of a cube. The problem is one of drawing the projections of a cube when one of its solid diagonals is perpendicular to the vertical plane. The solution for this problem, which is self-explanatory, is given in Fig. 14.1.
K. Rathnam

### Chapter 15. Perspective Projections

Perspective projection is a method of pictorial representation of an object on a transparent picture plane as seen by an observer stationed at a particular position relative to the object. The object is placed behind the picture plane, and the observer is stationed in front of the picture plane. The visual rays emanating from the eye of the observer to the object pierce the picture plane and locate the position of the object on the picture plane. The visual rays emanate from a common point known as the station point or the eye of the observer. This type of projection is called perspective projection. This is also known as scenographic projection or convergent/conical projection. The method of preparing a perspective view differs from the various other methods of projections discussed earlier.
K. Rathnam

### Chapter 16. Objective Type Questions

The multiple choice objective type questions with keys emphasise on elucidating the concepts. The questios framed are of varying degrees of difficulty. Finding answers will help the reader to assess his/her understanding of the subject. The questions help to kindle the imagination of its readers and inspire them to pursue this subject further.
K. Rathnam