ENGINEERING DRAWING (CHAPTER -10)


๐Ÿ“˜ 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.

๐Ÿ‘‰ 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

  1. Section Plane Perpendicular to HP, Parallel to VP

    • Cuts vertically → FV shows true shape of section.

  2. Section Plane Perpendicular to VP, Parallel to HP

    • Cuts horizontally → TV shows true shape.

  3. Section Plane Perpendicular to both HP and VP

    • Section appears as a line (edge view).

  4. Section Plane Inclined to HP or VP

    • Neither FV nor TV shows true shape → auxiliary projection needed.

10.4 Types of Sectional Views

  1. Full Section

    • Object cut fully by section plane.

    • One half is imagined removed.

  2. Half Section

    • Object cut by two perpendicular planes.

    • Used for symmetrical objects (e.g., bearings, bushes).

  3. Offset Section

    • Cutting plane is bent to pass through important features.

    • Useful when holes or slots are not in one straight line.

  4. Revolved Section

    • Section of a part is revolved 90° onto the drawing plane.

    • Used in shafts, spokes, ribs.

  5. Removed Section

    • Sectional view drawn away from the main drawing for clarity.

10.5 Hatching (Section Lines)

  • The cut surface is shown with thin, equally spaced, inclined lines (called hatching).

  • Standard angle: 45° (can be changed for adjacent parts).

  • Spacing: 2 to 3 mm apart, depending on size.

๐Ÿ‘‰ Hatching makes it clear which surface is cut.

10.6 Section of Different Solids

(A) Section of Prism

  • Example: Hexagonal prism cut by a plane perpendicular to VP, inclined to HP.

  • True shape of section is a polygon (depends on angle).

(B) Section of Pyramid

  • Example: Square pyramid cut by a plane parallel to base → section is a smaller square.

  • If cut by an inclined plane → section is trapezium.

(C) Section of Cylinder

  • Plane parallel to axis → section is a rectangle.

  • Plane perpendicular to axis → section is a circle.

  • Inclined plane → section is an ellipse.

(D) Section of Cone

  • Depending on cutting plane, we get conic sections:

    • Plane parallel to base → Circle

    • Inclined to axis → Ellipse

    • Parallel to generator → Parabola

    • Cutting both halves → Hyperbola

๐Ÿ‘‰ Thus, conic sections are obtained from cone sections.

(E) Section of Sphere

  • Any plane cut through sphere → Circle.

10.7 Auxiliary Views of Sections

  • When section plane is inclined, the true shape of section cannot be seen in FV or TV.

  • An auxiliary plane parallel to section plane is drawn to obtain the true shape of section.

10.8 Practical Applications

  • Machine Drawing → Bearings, pistons, valves, gears, shafts.

  • Civil Engineering → Sectional views of beams, columns, foundations.

  • Architecture → Sectional plans of buildings, rooms.

  • Design → Helps to visualize hidden parts clearly.

10.9 Summary of Chapter

  • Sectional views reveal hidden internal details of objects.

  • Section planes are shown with chain lines and arrows.

  • Types: Full, Half, Offset, Revolved, Removed sections.

  • Different solids give different sectional shapes (circle, ellipse, polygon, parabola, hyperbola).

  • Auxiliary projection shows true shape of inclined sections.


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