EDUCATIONAL BLOG

📘 ENGINEERING DRAWING Chapter 12 – Isometric Projection 12.1 Introduction In orthographic projection, we need multiple views (FV, TV, SV) to represent an object. But sometimes we need a single pictorial view that shows the 3D appearance . This is achieved by Isometric Projection . 👉 “Isometric” = equal measure (from Greek iso = equal, metron = measure). 12.2 Principle of Isometric Projection Object is imagined inside a transparent cube . Cube is tilted so that one of its body diagonals is perpendicular to the plane of projection. As a result: All three principal axes (X, Y, Z) are equally inclined (120° apart) . Scale along each axis is equally reduced (isometric scale) . 12.3 Isometric Axes and Planes Isometric Axes → Three lines meeting at a point at 120° angles . One vertical, two inclined at 30° to horizontal. Isometric Planes → Planes formed by any two isometric axes. They appear as parallelograms instead of squares....

📘 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...

📘 ENGINEERING DRAWING Chapter 5 – Geometrical Constructions 5.1 Introduction Geometrical constructions form the foundation of engineering drawing . They help in constructing angles, polygons, tangents, perpendiculars, bisectors, and divisions with accuracy using only compass, straightedge (scale), and set squares . These constructions are widely applied in mechanical drawings, civil plans, gear tooth profiles, cams, and machine parts . 5.2 Basic Constructions (A) Bisecting a Line Segment Steps: Draw a line AB. With A as center and radius > ½ AB, draw arcs above and below AB. With B as center and same radius, draw arcs to cut previous arcs. Join intersection points → perpendicular bisector of AB. 👉 This gives both the midpoint and right angle bisector . (B) Bisecting an Angle Steps: Draw ∠ABC. With B as center, draw an arc cutting BA and BC at D and E. With D and E as centers, draw arcs intersecting at F. Join BF → bisector of ∠ABC. (...

📘 ENGINEERING DRAWING Chapter 4 – Scales (Plain, Diagonal, Vernier) 4.1 Introduction In engineering drawing, objects are often too large (like buildings, bridges, ships) or too small (like watch parts, IC chips) to be drawn in their actual size on a sheet. 👉 Therefore, we use Scales to represent objects proportionally. Definition: A scale is a measuring device used to reproduce the dimensions of an object proportionally smaller or larger than its actual size. Example: A building 30 m long is represented as 300 mm on paper using a 1:100 scale . A small screw 5 mm long may be drawn as 50 mm on paper using a 10:1 scale . 4.2 Types of Scales (A) Full Scale When the drawing size = actual size. Ratio = 1:1 . Used when object fits comfortably on sheet. (B) Reducing Scale When the drawing is smaller than actual size. Ratio less than 1 (e.g., 1:2, 1:5, 1:10, 1:100). Used in maps, buildings, large machines . (C) Enlarging Scale When the...

📘 ENGINEERING DRAWING Chapter 3 – Lines, Lettering, and Dimensioning 3.1 Introduction In Engineering Drawing, lines, lettering, and dimensioning are the foundation . Lines → Represent shapes, edges, surfaces, and details. Lettering → Provides notes, titles, and labels in a clear readable style. Dimensioning → Specifies the size, location, and other details necessary for manufacturing. 3.2 Types of Lines (as per BIS: IS 10714 / SP-46) Different line types are used in technical drawings. Each has a specific meaning . Type of Line Appearance Thickness Use Continuous thick ——————— Thick Visible outlines, edges Continuous thin ——————— Thin Projection lines, dimension lines, leader lines, hatching Continuous thin freehand ~~~~~~~ Thin Short break lines Continuous thin with zig-zag _ ///_ Thin Long break lines Dashed thin – – – – – – Thin Hidden edges Chain thin –– ⃝ –– ⃝ –– Thin Center lines, axis, paths of motion Cha...

📘 ENGINEERING DRAWING Chapter 2 – Drawing Instruments and Their Uses 2.1 Introduction For preparing accurate engineering drawings, special drawing instruments are required. These instruments help to draw straight lines, circles, arcs, curves, and angles precisely according to international standards. Proper knowledge and correct handling of instruments are essential for producing neat and accurate work. 2.2 Types of Drawing Instruments (A) Drawing Board Made of well-seasoned softwood or plywood. Surface: Smooth, free from warping. Standard Sizes (as per IS:1444): Full size : 1000 × 700 mm Half size : 700 × 500 mm Quarter size : 500 × 350 mm Use : Base for fixing drawing sheet with clips or tape. (B) Drawing Sheet Made of good quality paper (cartridge or ivory paper). Standard sizes: A0 to A4 (ISO/BIS). Fixing method : With clips (T-square kept on left edge). Or using masking tape at corners. (C) Pencils Types: Graphite ...

📘 ENGINEERING DRAWING Chapter 1 – Introduction to Engineering Drawing 1.1 What is Engineering Drawing? Engineering Drawing is a graphic language of engineers and technicians. It is the universal language of engineering through which ideas, designs, and specifications are conveyed clearly and accurately. Unlike freehand sketches, engineering drawing follows international standards so that a drawing made in one country can be understood by engineers anywhere in the world. Definition : “Engineering Drawing is a language of lines, symbols, and notes used by engineers to convey information about objects, machines, structures, and systems.” Example : A machine designer in India can prepare a drawing of a gear, and the same drawing can be manufactured in Germany or Japan without confusion if proper drawing standards are followed. 1.2 Importance of Engineering Drawing Universal Language – It is understood across countries irrespective of spoken language. Communic...

📘 ENGINEERING DRAWING – Complete Notes Contents Introduction to Engineering Drawing Drawing Instruments and Their Uses Lines, Lettering, and Dimensioning Scales (Plain, Diagonal, Vernier Scales) Geometrical Constructions Engineering Curves (Ellipse, Parabola, Hyperbola, Cycloid, Involute, Spiral, Helix) Orthographic Projections – Principles Projection of Points, Lines, and Planes Projection of Solids (Prisms, Pyramids, Cylinders, Cones) Section of Solids Development of Surfaces Intersection of Solids Isometric Projection and Isometric Views Perspective Projection Computer-Aided Drafting (AutoCAD / CAD basics) Drawing Standards (BIS conventions, title blocks, symbols)

               INTRODUCTORY CONCEPTS                                PART-02 * About Protractor:- 📐 प्रोट्रैक्टर (Protractor) हिंदी में: प्रोट्रैक्टर एक इंजीनियरिंग और ज्यामिति में उपयोग किया जाने वाला माप उपकरण है, जिसका प्रयोग कोण (Angle) नापने और बनाने के लिए किया जाता है। यह आमतौर पर अर्धवृत्त (180°) या पूर्ण वृत्त (360°) के आकार का बना होता है। इसमें डिग्री (°) में माप की गई स्केल बनी होती है, जैसे 0° से 180° या 0° से 360° तक। इसका उपयोग मुख्य रूप से ड्रॉइंग, डिज़ाइन, मैकेनिकल ड्राफ्टिंग और इंजीनियरिंग ड्रॉइंग में किया जाता है। इंजीनियरिंग में विशेष प्रकार के प्रोट्रैक्टर मिलते हैं, जैसे Bevel Protractor , जिसका उपयोग बहुत सटीक कोण नापने और सेट करने के लिए होता है। उपयोग (Applications): कोण मापने में कोण बनाने में मशीन पार्ट्स या ड्रॉइंग में सटीक माप लेने में In English: A Protractor (Protector) is an engineering and geometry meas...