EDUCATIONAL BLOG

📘 ENGINEERING DRAWING Chapter 11 – Development of Surfaces 11.1 Introduction Development of a surface means unfolding or spreading out the surface of a 3D solid on a 2D plane . This gives the true size and shape of every face of the solid. It is essential in sheet-metal work (fabrication of pipes, hoppers, tanks, ducts, chimneys). Example: A cylinder can be developed into a rectangle . A cone can be developed into a sector of a circle . 11.2 Methods of Development Parallel Line Method Used for prisms and cylinders (since their sides are parallel). Radial Line Method Used for pyramids and cones (since their faces meet at a point). Triangulation Method Used for transition pieces (objects connecting different shapes, like square-to-round ducts). 11.3 Development of Specific Solids (A) Cube Development = 6 equal squares arranged in the shape of a cross . Applications: Packaging boxes. (B) Prism Example: Hexago...

📘 ENGINEERING DRAWING Chapter 10 – Section of Solids 10.1 Introduction In many cases, the inside details of an object cannot be understood from external views alone. To solve this, we imagine the object is cut by a plane (called section plane ) and then we project the cut surface. This method is called a sectional view . 👉 Sectional views are widely used in machine drawing, building drawing, and design drawings . 10.2 Section Planes (A) Definition A section plane (SP) is an imaginary plane that cuts through a solid. The intersection of SP and the solid is called the section . The shape of the section depends on the orientation of the cutting plane. (B) Representation Section plane is shown by a thin chain line with thick ends, often labeled as SP . Arrowheads on SP show the direction of viewing . 10.3 Types of Section Planes Section Plane Perpendicular to HP, Parallel to VP Cuts vertically → FV shows true shape of section. Se...

📘 ENGINEERING DRAWING Chapter 9 – Projection of Solids 9.1 Introduction A solid is a 3D object having length, breadth, and thickness . In engineering drawing, we represent these solids on 2D planes (HP & VP) using orthographic projection . Solids are used in machine design, civil structures, tools, models, and construction drawings . 9.2 Classification of Solids (A) Polyhedra (bounded by plane surfaces) Regular Polyhedra – All faces are equal regular polygons Tetrahedron (4 faces) Cube (6 square faces) Octahedron (8 triangular faces) Prism – Two bases are equal polygons, joined by rectangular faces Triangular prism, Square prism, Hexagonal prism, etc. Pyramid – A polygonal base with triangular faces meeting at a point (apex) Triangular pyramid, Square pyramid, Pentagonal pyramid, etc. (B) Solids of Revolution (formed by revolving a plane figure) Cylinder → rectangle revolved about one side Cone → right-angled triangl...

📘 ENGINEERING DRAWING Chapter 8 – Projection of Points, Lines, and Planes 8.1 Introduction Orthographic projection is based on projecting points, lines, and planes onto the principal reference planes: Horizontal Plane (HP) → Top view (plan) Vertical Plane (VP) → Front view (elevation) Profile Plane (PP) → Side views 👉 Any complex object is made up of points, lines, and planes. So, to understand projection of solids, we must first master these basics. 8.2 Projection of Points A point in space is defined by its distance from HP and VP. Quadrants The space around the reference planes is divided into four quadrants : First Quadrant → Point above HP and in front of VP Second Quadrant → Point above HP and behind VP Third Quadrant → Point below HP and behind VP Fourth Quadrant → Point below HP and in front of VP 👉 In First Angle Projection (India/Europe) , the object lies in the first quadrant . Example Point P is 25 mm above HP and 35 mm in...

📘 ENGINEERING DRAWING Chapter 7 – Orthographic Projections (Principles) 7.1 Introduction An engineer must represent a 3D object (machines, buildings, structures) on a 2D drawing sheet . This is done using Projection . Definition: Projection is the method of representing the shape and size of an object on a 2D plane by drawing straight lines from the object to the plane. 7.2 Types of Projection Perspective Projection Rays converge to a point (eye). Objects look realistic (like human vision). Not used in engineering (distorted scale). Parallel Projection Rays are parallel (imaginary projectors). True shape and size preserved. Subtypes: Orthographic Projection (perpendicular projectors). Oblique Projection (inclined projectors). Axonometric Projection (isometric, dimetric, trimetric). 👉 Engineering drawing mainly uses Orthographic Projection . 7.3 Principle of Orthographic Projection Object is imagined inside a Glass B...

📘 ENGINEERING DRAWING Chapter 6 – Engineering Curves 6.1 Introduction In engineering, certain special curves frequently appear in the design of gears, cams, springs, bridges, trusses, aeroplane wings, turbines, and machine parts . These are not just mathematical curves but have direct engineering applications . The main engineering curves are: Conic Sections – Ellipse, Parabola, Hyperbola Cycloidal Curves – Cycloid, Epicycloid, Hypocycloid Involute Spirals – Archimedean Spiral, Logarithmic Spiral Helix – Cylindrical Helix, Conical Helix 6.2 Conic Sections A conic is obtained when a right circular cone is cut by a plane at different inclinations. Ellipse – Obtained when plane cuts the cone at an angle smaller than side of cone. Parabola – Obtained when plane is parallel to the generator of cone. Hyperbola – Obtained when plane cuts both halves of the cone. (A) Ellipse Definition: The locus of a point moving in a plane such that the su...