Engineering Drawing: Essential Concepts and Techniques

Posted on Mar 2, 2025 in Mechanical Engineering

Unit 6: Development of Surfaces

1. What is the Significance of Development?

Development is a graphical method of obtaining the area of the surfaces of a solid. In engineering, many objects cannot be manufactured by conventional manufacturing processes because of their size and shape. Thus, they are fabricated using the development phenomenon from metal sheets. Some examples include boiler shells and chimneys, pressure vessels, shovels, trays, boxes and cartons, feeding hoppers, large pipe sections, body and parts of automotives, ships, airplanes, and many more.

2. What are the Different Theories Used in the Development of Solids?

The different theories used in the development of solids are as follows:

  • Parallel Line Theory
  • Radial Line Theory

3. What is Radial Line Theory?

Radial line theory is employed to develop the surfaces of pyramids and cones. An arc of radius equal to the slant edge/generator is drawn, and the lateral faces/curved face are marked properly inside the arc.

4. What is Parallel Line Theory?

Parallel line theory is employed to develop the surfaces of prisms and cylinders. Two parallel lines are drawn from two ends of the solids, and the lateral faces are marked between these lines.

5. What are the Differences Between Parallel and Radial Line Theory?

The differences are as follows:

  • Parallel line theory is employed to develop the surfaces of prisms and cylinders, whereas radial line theory is employed to develop the surfaces of pyramids and cones.
  • In parallel line theory, two parallel lines are drawn from two ends of the solids, and the lateral faces are marked between these lines. Whereas, in radial line theory, an arc of radius equal to the slant edge/generator is drawn, and the lateral faces/curved face are marked properly inside the arc.

Unit 5: Isometric Views

1. What are Isometric View, Isometric Axes, Isometric Plane, and Isometric Lines?

Isometric View: It is a pictorial 3D representation in which all three views (front view, top view, and side view) are equally viewed in their actual dimensions, inclined at 120° to each other.

Isometric Axes: The axes that are equally inclined at 120° to each other so that all three views can be viewed equally.

Isometric Plane: The plane that is generated from the isometric axes and lines is called an isometric plane or isoplane.

Isometric Lines: The lines parallel to the isometric axes are called isometric lines.

2. What is Isometric Scale?

Isometric scale is the ratio of the isometric length to the actual length.

3. What is Isometric Projection?

Isometric projection is the projection constructed using an isometric scale in which the dimension in this projection is smaller than the true dimensions.

4. What is the Difference Between Isometric View and Projection?

Isometric view is a pictorial 3D representation in which all three views (front view, top view, and side view) are equally viewed in their actual dimensions, inclined at 120° to each other. Whereas isometric projection is the projection constructed using an isometric scale in which the dimension in this projection is smaller than the true dimensions.

5. What is the Difference Between Isometric View and Orthographic Projection?

In isometric projection, only one view on a plane is drawn to represent the three dimensions of an object. Whereas in orthographic view, two or three views are drawn to understand the object clearly.

Unit 4: Sectioning

1. What is the Significance of Sectioning?

By using orthographic projection, it becomes difficult to visualize the internal structures of an object. Thus, sectioning is done to reveal the internal cross-sectional shape and to reduce the hidden lines in the view.

2. What is a Cutting Plane?

A cutting plane is a plane that imaginarily cuts the object to reveal the internal features.

3. What are Hatched or Sectioned Lines?

Section lines or cross-hatch lines are those lines that indicate the surfaces that are cut by the cutting plane. The hatch must be inclined at 45° with a spacing of 2-3mm between the lines. All the lines should be uniformly spaced. Also, thin sections may be blackened in completely.

4. What are the Different Types of Sectioning?

The different types of sectioning are:

  • Full Sectioning: 50% of the material is removed.
  • Half Sectioning: 25% of the material is removed.
  • Offset Sectioning: The view is made by passing the bended cutting plane completely through the part.
  • Broken-out Section
  • Revolved Section (Aligned Section)
  • Removed Section (Detailed Section)

Unit 3: Orthographic Projections

1. What is Orthographic Projection?

Orthographic projection is a multi-view projection in which two or three views of the object are drawn at different planes of projection (POPs). In this projection, mutually parallel projectors are drawn perpendicular to the POPs.

2. What is the 1st Angle of Projection?

In the 1st angle of projection, the object is placed in the first quadrant, in which the front view (FV) is above and the top view (TV) is below the X-Y reference. Also, in this projection, the left-hand side view (LHSV) is drawn on the right-hand side of the FV, and the right-hand side view (RHSV) is drawn to the left.

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3. What is the 3rd Angle of Projection?

In the 3rd angle of projection, the object is placed in the third quadrant, in which the FV is below and the TV is above the X-Y reference. Also, in this projection, the LHSV is drawn on the left-hand side of the FV, and the RHSV is drawn to the right.

4. What are the Differences Between 1st and 3rd Angle of Projection?

The differences between 1st and 3rd angle of projection are:

1st Angle Projection

  1. FV above XY
  2. TV below XY
  3. LHSV is on the right side of FV
  4. RHSV is on the left side of FV

3rd Angle Projection

  1. FV is below XY
  2. TV is above XY
  3. LHSV is on the left side of FV
  4. RHSV is on the right side of FV

5. What are the Basic Elements of Projection?

There are three elements of projection:

  • Observer
  • Object
  • Plane of Projection

6. Draw the Symbols of First and Third Angle of Projection.

(Image is above)

Unit 2: Points and Traces

1. A Point A Lies 30mm Above the HP and 25mm in Front of the VP. Name the Quadrant in Which the Point is Lying.

Answer: First angle of projection.

2. A Point B is 70mm Above HP and 35mm Behind VP. Name the Quadrant in Which the Point is Lying.

Answer: Second angle of projection.

3. A Point C Lies 30mm Below the HP and 25mm Behind VP. Name the Quadrant in Which the Point is Lying.

Answer: Third angle of projection.

4. A Point D is 70mm Below HP and 35mm in Front of VP. Name the Quadrant in Which the Point is Lying.

Answer: Fourth angle of projection.

5. What are Traces and Their Types?

The point of impression at which the straight line, if produced necessary, meets the HP or VP is called a trace.

Types are:

  • Horizontal Trace (HT): When a straight line is inclined to HP, then the point of intersection of the line to the HP is called the horizontal trace.
  • Vertical Trace (VT): When a straight line is inclined to VP, then the point of intersection of the line to the VP is called the vertical trace.

Unit 1: Introduction to Engineering Drawing

1. What is the Significance of Engineering Drawing?

Engineering drawing is a technical language used by engineers to communicate ideas and the purpose of objects. It is also known as the grammar of engineering. It is a technical 2D representation of 3D figures which gives us precise information about the object to be produced.

2. What are the Different Types of Drawing Instruments Used in Engineering Drawing?

The different types of drawing instruments used in Engineering Drawing are as follows:

  • Drawing sheets, clips, and board
  • Drafter
  • T-square
  • Set-squares
  • Roller scale, compasses, and protractor
  • Lead pencils and eraser
  • French Curves
  • Lettering Template

3. What are the Different Types of Lines Used in Engineering Drawing?

The different types of lines used in engineering drawing are as follows:

  • Thin Continuous line (e.g., Dimension line, Projection line, Sectioning lines, etc.) [0.13mm]
  • Medium Continuous line (e.g., Reference line in projection, visible outline of sectioned surface) [0.25mm]
  • Thin long dashed dotted line (e.g., Centerlines, cutting planes)
  • Thin dashed line (hidden lines)
  • Continuous zigzag line (e.g., long break lines)

4. What are the Elements of Dimensioning?

The elements of dimensioning are as follows:

  • Extension line
  • Dimension line
  • Arrowheads
  • Dimension

5. What are the Different Systems of Dimensioning?

There are two different ways of dimensioning:

  • Aligned System: In this system, the dimensions are placed perpendicular to the dimension lines so that they may be read from the bottom of the grid sheet.
  • Unidirectional System: In this system, the dimensions are placed in such a way that they can be read from the bottom edge of the drawing sheet.

6. Difference Between Aligned and Unidirectional Dimensioning?

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The difference between Aligned and unidirectional dimensioning are stated as follows: In Aligned system, horizontal and inclined dimensions are read from the bottom of grid sheet and vertical dimensions are read from the right hand side of the sheet. In Unidirectional system, horizontal dimensions are place above the mid point of the dimension line and vertical and inclined dimensions are marked by breaking the dimension line in the middle.

7. What are the Rules of Dimensioning?

The rules of dimensioning are as follows:

  • Between any two extension lines, there must be only one dimension.
  • All the dimensions should be placed outside the views.
  • All the dimensions on a drawing must be shown using either aligned or unidirectional systems.
  • The same unit of length must be used for all the dimensions on a drawing.
  • Dimension lines must not cross each other.
  • All dimensions must be given.
  • Each dimension should be given only once.

8. What are the Different Types of Dimensioning?

The different types of dimensioning are:

  • Chain Dimensioning (Continuous Dimensioning)
  • Parallel Dimensioning (Progressive Dimensioning)
  • Combined Dimensioning

9. What are the Different Types of Scales Used in Engineering Drawing?

The different types of scales used in engineering drawing are as follows:

  • Plain Scale
  • Diagonal Scale
  • Vernier Scale
  • Scale of Chords
  • Comparative Scales

10. What is Representative Fraction (RF) in Scales?

RF is defined as the ratio of the length of the object on the drawing to the actual length of the object.

11. What is Enlarging or Enlargement Scale?

When smaller objects are to be drawn, they are often enlarged. In other words, when the RF > 1, this scale is called an enlarging scale.

12. What is Reducing or Reduction Scale?

When larger objects are to be drawn, they are often reduced. In other words, when the RF < 1, this scale is called a reducing scale.

13. What is Full Scale?

When the object is drawn on the sheet to its actual size, it is said to be drawn in full scale (RF = 1).

14. What is Length of Scale (LOS)?

All scales are generally constructed by drawing a line representing the actual distance to be represented. This length is called LOS.

LOS = RF x Maximum distance to be represented

15. What is Plain Scale?

Plain scale is a scale used to indicate distance in a unit and its immediate subunits.

16. What is Diagonal Scale?

Diagonal scale is a scale used to indicate distances in a unit and its immediate two subdivisions.

What Happens in Aligned Dimensioning?

  • Horizontal and inclined dimensions are read from the bottom of the grid sheet, and vertical dimensions are read from the right-hand side of the sheet.