Engineering Drawing: A Complete Guide

What is Drawing?

The graphical representation of any idea or object is called drawing. Drawing can be prepared either by:

• Using free hand
• Using drawing instruments
• Using computer programs

Types of Drawing

There are two types of drawing:

• Artistic Drawing
• Engineering Drawing

Artistic Drawing

The drawing representing any object or idea which is sketched in free hand using the imagination of an artist is called artistic drawing.

• Proper scaling and dimensioning is not maintained in artistic drawing.
• Artistic drawings are used to express aesthetic, philosophical, and abstract ideas.
• Examples: Paintings, Posters, Arts.

Engineering Drawing

Engineering Drawing is the graphical representation of any idea or object which expresses technical details without the barrier of a language and communicates ideas and information from one mind to another.

• Engineering Drawing is the “Universal Language for Engineers”.
• One picture/drawing is equivalent to several sentences.
• Drawings are also necessary for engineering industries since they are required and are being used at various stages of development of an engineering product.

Difference between Artistic and Engineering Drawing

Objectives of Engineering Drawing

Objectives of Drawing are as follows:

• To achieve the geometric form of the design.
• To communicate ideas between designers and manufacturing personnel.
• To act as an analysis tool, missing dimensions and tolerances are calculated on the drawing as it is developed.
• To simulate the design.
• To act as an extension of the designer's short-term memory, designers often unconsciously make sketches to help them remember ideas that they might otherwise forget.

Importance of Engineering Drawing to Civil Engineers

Importance of engineering drawing to civil engineers is as follows:

• Engineering Drawing enables one to suitably depict complex systems on a piece of paper with almost all critical information associated with it.
• For Civil Engineers, these complex systems could be buildings, dams, roads, railways, services in buildings, and other infrastructure components.
• Before any structure comes into existence in real time, Civil Engineers first need to create the drawings of the desired structure.
• It helps in preparing the bill of quantities.
• It helps in preparing cost estimation.
• It helps to improve the initial design.
• Engineering drawing acts as the language of engineers.

Applications of Engineering Drawing

Applications of Engineering Drawing are as follows:

• It is used in ships for navigation.
• For manufacturing of machines, automobiles, etc.
• For construction of buildings, roads, bridges, dams, electrical and telecommunication structures, etc.
• For manufacturing of electrical appliances like TV, Phone, Computers, etc.

Types of Engineering Drawing

1. Geometrical Drawing

   The art of representing geometric objects such as rectangles, squares, cubes, cones, cylinders, spheres, etc., on paper is called geometric drawing.

   • Plane Geometrical Drawing:
     • If the object has only 2 dimensions, i.e., length and breadth, it is called Plane geometrical drawing.
     • Examples: Rectangles, Squares, Triangles, etc.
   • Solid Geometrical Drawing:
     • If the object has 3 dimensions, i.e., length, breadth, and thickness/depth, it is called Solid geometrical drawing.
     • Examples: Cube, Sphere, Prism, Cylinder, etc.
2. Mechanical Engineering Drawing

   The art of representing mechanical engineering objects such as machines, machine parts, etc., on paper is called mechanical engineering drawing or machine drawing.

   It is used by mechanical engineers to express mechanical engineering works and projects for actual execution.

3. Civil Engineering Drawing

   The art of representing civil engineering objects such as buildings, roads, bridges, dams, etc., on paper is called civil engineering drawing.

   It is used by civil engineers to express civil engineering works and projects for actual execution.

   There are two types of Civil Engineering Drawing:

   • Architectural Drawing:
     • Plan:
       • It shows the position of different objects and elements of the structure in a two-dimensional view.
       • View along the top of the structure is called a plan.
       • Only length and width of objects are shown here.
     • Elevation and Section:
       • It shows a view along the height of the structure.
       • In elevation view, either height and length or height and width are shown.
   • Structural Drawing:
     • It shows the detailed requirement of reinforcement and their arrangement in the structure.
     • It also shows the specification and properties of construction materials like concrete, steel, timber, etc.
4. Electrical & Electronics Engineering Drawing

   The art of representing electrical engineering objects such as motors, generators, transformers, wiring diagrams, etc., on paper is called electrical engineering drawing.

   It is used by electrical engineers to express electrical engineering works and projects for actual execution.

   The art of representing electronic circuits of TV, Phones, computers, etc., on paper is called electronic engineering drawing or electronic drawing.

   It is used by electronic engineers to express electronic engineering works and projects for actual execution.

Elements of Engineering Drawing

Figure 1: Elements of Engineering Drawing

Drawing Standards

There are some drawing standards or drawing codes that accumulate the rules of engineering drawing for a certain region.

Well-known drawing codes and their application regions are expressed below:

In Nepal, it is usual practice to follow ISO standards. However, in some instances, ANSI, BS, etc., are also used.

Drawing Instruments and Accessories / Drafting Tools and Equipment

Following instruments and accessories are required to achieve perfection in manual drawing:

1. Drawing Board

• Drawing board is made of softwoods.
• Almost perfect planning of the working surface of the drawing board is to be ensured.
• A strip of hard ebony edge is fitted in a groove on the shorter edge of the board and perfectly lined to provide the guide for the T-square.
• The main parts of the drawing board are the working surface, battens, and ebony working edge.

Table 1: Standard Drawing Board Sizes

2. Drawing Sheet

• Drawing sheet is the medium on which drawings are prepared by means of pencils or pens.
• Drawing sheets are available in standard sizes.
• A standard A0 size sheet is the one with an area of 1 m² and dimensions of 1189 × 841 mm.
• Each higher-numbered sheet (A1, A2, A3, etc., in order) is half the size of the immediately lower-numbered sheet.
• The sides of each size drawing sheet are in the ratio of 1:√2.

Table 2: Standard Sizes of Drawing Sheets

Figure 2: Recommended Sizes Obtained for Various Drawing Sheets

3. Mini Drafter

• This is a device used to draw horizontal, vertical, and inclined lines very effectively.
• It is mounted on the top left corner of the drawing board by means of a clamping mechanism, which is an integral part of the device.
• An L-shaped scale, graduated in millimeters, acts as the working edge of the mini-drafter.
• The L-shaped scale also has a degree scale for angle measurement.
• The working edge can be moved to any desired location on the drawing board.

Figure 3: Mini Drafter

4. T-Square

• It is made of hardwood, plastic, or celluloid.
• It has two parts: Stock and Blade.
• The stock is used to move the T-square along the working face of the drawing board.
• The blade may be used as a base for set squares as well as to draw horizontal lines.
• The stock of the T-square makes a 90-degree angle with the working edge (blade).
• Stock and blade are joined together at a right angle to each other by means of screws.

Figure 4: T-Square

Table 3: T-Square Standard Sizes

5. Set Squares

• Set squares are a set of 45° set squares and 30°-60° set squares.
• They are used in conjunction with each other and with the T-square to draw parallel, inclined, and perpendicular lines.
• The 45° set square generally has a protractor, whereas the 30°-60° set square includes French curves.

Figure 5: Set Squares

6. Compasses

• These are used to draw arcs or circles.
• Each compass consists of a needle point and a pencil point.
• Lengthening bars are used to draw very large circles, bow compasses are used to draw small circles, and drop compasses are used to draw very small circles.
• Lengthening bars are used to draw circles of radius greater than 150 mm, bow compasses are used to draw circles of radius 25 mm to 150 mm, and drop compasses (also called small bow compasses) are used to draw circles with a radius less than 25 mm.

Figure 6: Compass

7. Divider

• Dividers are used to transfer lengths to the drawings either from scales or from the drawing itself.
• Similar to compasses, two sizes of dividers are used in technical drawings: one large divider and one small spring bow divider.

Figure 7: Divider

8. Pencils / Lead Sticks / Pencil Sharpener / Eraser / Wiper

• The primary tool used in technical drawings is the pencil or lead sticks.
• Generally, for technical drawings, the three grades of pencils used are HB, H, and 2H.
• H stands for hardness, and B stands for blackness.
• Pencil sharpeners are used to mend pencils.
• Erasers are used to erase unnecessary parts of the pencil drawing, and unwanted matter produced due to the use of erasers should be removed with the help of a wiper.

Figure 8: Pencil Grades

9. French Curves / Flexible Curves

• French curves are free-form templates made of acrylic and are used to draw smooth curves passing through a number of points.
• The outer profile of the French curve is adjusted so that the smooth curve passes through more than three points, and a curve passing through these points is drawn.
• The next part of the curve is then drawn by using the next three points in addition to the last two points of the previous curve.
• A flexible curve consists of a flexible material, generally made of metallic wire coated with thick rubber material.
• This can be bent into any shape so that its working edge can be matched with a number of points, and a smooth curve can be drawn.

Figure 9: French Curve

10. Protractor

• It is used for laying out and measuring angles.

Figure 10: Protractor

11. Scotch Tape or Drawing Pin

• Transparent tape is used to stick the drawing sheet on the drawing board, which is known as Scotch tape. This tape is applied at the corners of the sheet.
• Drawing pins can also be used for sticking the drawing sheet, but they are usually not preferred.

Drawing Sheet and Its Essential Components

• Every engineering drawing has to follow a standard format.
• The drawing sheet consists of drawing space, a title block, and sufficient margins.
• After fixing the drawing sheet on the drawing board, margins should be drawn.
• The layout should facilitate quick reading of important particulars.
• Drawings are prepared at various locations and shared, and quick references should be located easily.

Figure 11: Drawing Sheet Layout

a) Borders

• Space left all around between the trimmed edges of the sheet.
• A minimum of 10 mm, ISO Standard.
• Margin/Border of paper can be increased according to requirements and the setting of the printer/plotter.

b) Filling Margin

• 20 mm minimum on the left-hand side, including the border.
• This is provided for taking perforations.

c) Grid Reference System

• Used in all sizes of drawing sheets for easy location of the drawing within the frame.
• The length and width of the frames are divided into an even number of divisions.
• The length of the grids lies between 25 mm to 75 mm, depending on the drawing sheet size, and the thickness is 5 mm.
• The grids along vertical edges are named by capital letters, whereas grids along horizontal edges are named by numerals.
• Numbering and lettering start from the corner of the sheet opposite to the title box and are repeated on the opposite sides.
• Repetition of letters or numbers like AA, BB, etc., is practiced in case they exceed the number of alphabets.

d) Title Box

• An important feature that is a must in every drawing sheet.
• The title box is drawn at the bottom right-hand corner of every drawing sheet and provides technical and administrative details regarding the drawing/component.
• ISO-recommended sizes of the title box are 180 mm × 27 mm and 180 mm × 36 mm.
• Generally, the used size of the title block is 180 mm × 65 mm (BIS Standard).
• The title box is divided into two zones:
  • Part Identification Zone: Details like the identification number or part number, title of the drawing, legal owner of the drawing, etc., are mentioned here.
  • Additional Information Zone: Indicative items like symbols indicating the system of projection, scale used, etc., technical items like the method of surface texture, tolerances, etc., and other administrative items are mentioned here.

Figure 12: Title Block

Lettering

• Lettering is used for writing titles, sub-titles, dimensions, scales, and other details on a drawing.
• The style of writing letters and numerals used in engineering drawing may be vertical or inclined. Inclined lettering is usually done at an inclination of 75 degrees.
• Lettering types generally used for creating a drawing are:
  • Lettering A: Height of the capital letter is divided into 14 equal parts.
  • Lettering B: Height of the capital letter is divided into 10 equal parts.

Figure 13: Typical Lettering Features

Heights of Letters and Numerals

• The height of the capital letters is equal to the height of the numerals used in dimensioning.

Table 4: The Letter Sizes Recommended for Various Items

Lines in Engineering Drawing

Just as in an English textbook, correct words are used to make correct sentences; in Engineering Graphics, the details of various objects are drawn by different types of lines. Each line has a definite meaning and sense to convey.

Types of Lines

• Visible Outlines, Visible Edges: (Continuous wide lines) The lines drawn to represent the visible outlines/visible edges/surface boundary lines of objects should be outstanding in appearance.
• Dimension Lines: (Continuous narrow lines) Dimension lines are drawn to mark dimensions.
• Extension Lines: (Continuous narrow lines) These are extended slightly beyond the respective dimension lines.
• Construction Lines: (Continuous narrow lines) These are drawn for constructing drawings and should not be erased after completion of the drawing.
• Hatching / Section Lines: (Continuous narrow lines) These are drawn for the sectioned portion of an object. These are drawn inclined at an angle of 45° to the axis or to the main outline of the section.
• Guide Lines: (Continuous narrow lines) These are drawn for lettering and should not be erased after lettering.
• Break Lines: (Continuous narrow freehand lines) Wavy continuous narrow lines drawn freehand are used to represent the break of an object.
• Break Lines: (Continuous narrow lines with zigzags) Straight continuous narrow lines with zigzags are used to represent the break of an object.
• Dashed Narrow Lines: (Dashed narrow lines) Hidden edges/hidden outlines of objects are shown by dashed lines of short dashes of equal lengths of about 3 mm, spaced at equal distances of about 1 mm. The points of intersection of these lines with the outlines/another hidden line should be clearly shown.
• Center Lines: (Long-dashed dotted narrow lines) These are drawn at the center of the drawings symmetrical about an axis or both axes. These are extended by a short distance beyond the outline of the drawing.
• Cutting Plane Lines: Cutting plane lines are drawn to show the location of a cutting plane. It is a long-dashed dotted narrow line, made wide at the ends, bends, and changes of direction. The direction of viewing is shown by means of arrows resting on the cutting plane line.
• Border Lines: Border lines are continuous wide lines of minimum thickness 0.7 mm.

Dimensioning

The size information of an object is expressed by means of dimensioning in a drawing. These dimensions indicated should be those that are essential for the production, inspection, and functioning of the object.

The dimensions are written either above the dimension lines or inserted at the middle by breaking the dimension lines.

Normally, two types of dimensioning systems exist: Unidirectional system and Aligned system.

Types of Dimensioning Systems

• Unidirectional System:
  • The dimensions are so oriented such that they can be read from the bottom of the drawing.
  • It is also known as the horizontal system.
  • This system is preferred to the aligned system.
• Aligned System:
  • All the dimensions are oriented to be read from the bottom or right side of the drawing.
  • In the aligned system, the dimensions are placed perpendicular to the dimension line.

Figure 5: (a) Unidirectional System (b) Aligned System of Dimensioning

Arrangements of Dimensions

1. Chain Dimensioning:
   • Also called continuous or feature-to-feature dimensioning.
   • Commonly used and easy to insert.
2. Baseline Dimensioning:
   • Also called parallel dimensioning.
   • It is used when the location of features must be controlled from a common reference point or plane.
3. Overall Dimensioning:
   • Also called combined dimensioning.
   • When several dimensions make up the overall length, the overall dimension can be shown outside these component dimensions.
4. Auxiliary Dimensioning:
   • Also called reference dimensioning.
   • When all of the component dimensions must be specified, an overall length may still be specified as an auxiliary dimension.
   • Auxiliary dimensions never have tolerance and are shown in brackets.

Rules to be Followed in Dimensioning

• Each feature is dimensioned and positioned only once.
• Each feature is dimensioned and positioned where its shape shows.
• Size dimensions – give the size of the component.
• Every solid has three dimensions; each of the geometric shapes making up the object must have its height, width, and depth indicated in the dimensioning.
• A gap of 1 mm has to be kept between the extension line and the visible line.
• An extension line should be extended about 3 mm from the outermost dimension line.
• Extension lines may cross each other without a break.
• Center lines can be used as extension lines.
• Extension lines are drawn usually perpendicular to dimension lines.

Components of Dimensioning

• Dimension Lines:
  • Dimension lines should be placed at least 10 mm away from the outline.
  • Other parallel dimensions should be at least 6 mm apart, or more, if space permits.
• Extension Lines:
  • A thin, solid line perpendicular to a dimension line, indicating which feature is associated with the dimension.
  • There should be a visible gap of 1 mm between the feature’s corners and the end of the extension line.
• Leader Lines:
  • Leaders are used in engineering drawing for dimensioning arcs, circles, etc.
  • They are also used to present notes, symbols, item numbers, or part numbers, etc.
  • A leader should be terminated by either an arrowhead or a small dot of about 1.5 mm diameter.
  • Leaders should not be drawn bent unless necessary.
  • Leaders should not cross each other.
  • All notes, symbols, and dimensions in a leader need to be provided in a horizontal direction.
• Arrows:
  • 3 mm long and should be 1/3rd as wide as they are long - symbols placed at the end of dimension lines to show the limits of the dimension.
  • Arrows are uniform in size and style, regardless of the size of the drawing.

Figure 10: Various Types of Arrows Used in Dimensioning

Scales

There is a wide variation in sizes for engineering objects; some are very large, and some are very small. There is a need to reduce or enlarge while drawing the objects on paper. The proportion by which the drawing of an object is enlarged or reduced is called the scale of the drawing.

A scale is defined as the ratio of the linear dimensions of the object as represented in a drawing to the actual dimensions of the same.

Drawings drawn with the same size as the objects are called full-sized drawings. It is not convenient, always, to draw drawings of the object to its actual size, such as buildings, heavy machines, bridges, watches, electronic devices, etc.

Hence, scales are used to prepare drawings at:

• Full size
• Reduced size
• Enlarged size

Types of Scales

• Reducing Scales:
  • 1:Y (Y > 1)
  • Examples: 1:2, 1:20, 1:200, 1:2000, 1:5, 1:50, 1:500, 1:5000
• Enlarging Scales:
  • Y:1 (Y > 1)
  • Examples: 2:1, 20:1, 200:1, 2000:1, 5:1, 50:1, 500:1, 5000:1
• Full Size Scales:
  • 1:1
  • Examples: 10:1, 100:1, 1000:1, 10000:1

Information Necessary for Construction of Scale

Following are the necessary information required for the construction of a scale:

1. The representative fraction (R.F.) of the scale.
2. The unit or units to be presented.
3. The maximum length to be measured.

Representative Fraction (R.F.) or Scale Factor (S.F.)

The ratio of the length of the drawing to the corresponding actual length of the object is known as the representative fraction (R.F.) or the scale factor (S.F.).

It is to be remembered that for finding R.F., the distances used for calculation must be in the same unit. Being a ratio of the same units, R.F. itself has no unit.

Formula:

R.F. = Length of an object on the drawing / Actual length of the object

Example: When 1 cm long line in the drawing represents 1 m length of the object,

R.F. = 1 cm / (1 × 100 cm) = 1/100

Length of Scale = R.F. × Maximum length to be measured

Polygon

• Magnitude of any internal angle: (n - 2) × 180° / n, where n = number of sides.
• Radius of circumscribing circle: S / (2 × sin(π / n)), where S = length of each side and n = number of sides.
• Number of diagonals: n(n - 3) / 2, where n = number of sides.

Cone and Conic Sections

A cone is formed when a right-angled triangle with an apex and angle θ is rotated about its altitude as the axis. The length or height of the cone is equal to the altitude of the triangle, and the radius of the base of the cone is equal to the base of the triangle. The apex angle of the cone is 2θ.

When a cone is cut by a plane, the curve formed along the section is known as a conic. For this purpose, the cone may be cut by different section planes, and the conic sections obtained are shown in the figures below.

Ellipse

When a cone is cut by a section plane B-B at an angle, α, more than half of the apex angle (i.e., θ) and less than 90°, the curve of the section is an ellipse. Its size depends on the angle α and the distance of the section plane from the apex of the cone.

An ellipse is also defined as a curve traced by a point moving in a plane such that the sum of its distances from two fixed points is always the same.

Parabola

If the angle α is equal to θ (i.e., when the section plane C-C is parallel to the slant side of the cone), the curve at the section is a parabola. This is not a closed figure like a circle or ellipse. The size of the parabola depends upon the distance of the section plane from the slant side of the cone.

Hyperbola

If the angle α is less than θ (section plane D-D), the curve at the section is a hyperbola. The curve of intersection is a hyperbola, even if α = θ, provided the section plane is not passing through the apex of the cone. However, if the section plane passes through the apex, the section produced is an isosceles triangle.

Eccentricity

• Conic is defined as the locus of a point moving in a plane such that the ratio of its distance from a fixed point and a fixed straight line is always constant. The ratio is called eccentricity.
• Fixed point is called Focus.
• Fixed line is called Directrix.
• The line passing through the focus and perpendicular to the directrix is the axis of the curve. The point at which the conic section intersects the axis is called the vertex or apex of the curve.

When eccentricity:

• < 1: Ellipse
• = 1: Parabola
• > 1: Hyperbola

Roulettes

Roulettes are curves generated by the rolling contact of one curve or line on another curve or line, without slipping. The most common types of roulettes used in engineering practice are: Cycloids, Trochoids, and Involutes.

Cycloid

A Cycloid is generated by a point on the circumference of a circle rolling along a straight line without slipping.

Epicycloid

The cycloid is called Epicycloid when the generating circle rolls along another circle outside it.

Hypocycloid

Hypocycloid is obtained when the generating circle rolls along another circle inside it.

Trochoid

Trochoid is a curve generated by a point outside or inside the circle rolling along a straight line.

• If the point is outside the circle, the curve obtained is called Superior Trochoid.
• If the point is inside the circle, the curve obtained is called Inferior Trochoid.

Involute

An Involute is a curve traced by the free end of a thread unwound from a circle or a polygon in such a way that the thread is always tight and tangential to the circle or side of the polygon. The tangent to the circle at any point on it is always normal to its involute.

Spiral

It is a curve generated by a point that revolves around a fixed point and at the same time moves towards it.

Helix

It is a curve generated by a point that moves around the surface of a right circular cylinder/cone and at the same time advances in the axial direction at a speed bearing a constant ratio to the speed of rotation.

Projection

• In engineering, 3-dimensional objects and structures are represented graphically on a 2-dimensional medium.
• The act of obtaining an image of an object is known as "Projection."
• The image obtained by projection is known as a "View."

Projection System

• All projection theories are based on two variables:
  1. Line of Sight/Projector: The lines or rays drawn from the observer to the object and to the plane are called lines of sight or projectors.
  2. Plane of Projection: An imaginary flat plane upon which the image created by the line of sight is projected. The image is produced by connecting the points where the lines of sight pierce the projection plane. In effect, a 3-D object is transformed into a 2-D representation, also called projections.

Projection Techniques

• There are generally two types of projection techniques:
  1. Parallel Projection: All lines of sight are parallel, and the observer is assumed to be stationed at an infinite distance from the object. This technique is commonly used.
  2. Perspective Projection: The observer is assumed to be stationed at a finite distance from the object. The height of the object appears to reduce as we move away from the observer. In this technique, all lines of sight start at a single point.

Parallel vs Perspective Projection

• Parallel Projection:
  • Distance from the observer to the object is infinite.
  • Projection lines are parallel.
  • The object is positioned at infinity.
• Perspective Projection:
  • Distance from the observer to the object is finite, and the object is viewed from a single point.
  • Projectors are not parallel.
  • Perspective projection mimics what the human eyes see, but it is difficult to draw.

Types of Projection

• There are generally four types of projection:
  1. Orthographic/Multi-view Projection: 'ORTHO' means right angle, and orthographic means right-angled drawing. When the projectors are perpendicular to the plane on which the projection is obtained, it is known as orthographic projection. Six views are possible in orthographic projection: top view, front view, left view, right view, rear view, and bottom view.
  2. Axonometric Projection: A type of pictorial projection where the object appears to be rotated to show all three dimensions. It includes isometric, dimetric, and trimetric projections.
  3. Oblique Projection: A type of parallel pictorial projection where projectors are parallel but not perpendicular to the picture plane. The angle is usually kept between 15° and 45°.
  4. Perspective Projection: A type of pictorial projection where projectors are not parallel and converge to a point, mimicking the human eye's view.

Axonometric Projection

• Axonometric projection is a type of parallel pictorial projection where the object appears to be rotated to show all three dimensions.
• It is one of the four principal projection techniques: multi-view, axonometric, oblique, and perspective projection.
• Axonometric projections are of three types:
  1. Isometric Projection: All three axes are equally foreshortened, and the angles between them are 120°.
  2. Dimetric Projection: Two of the three axes appear equally shortened.
  3. Trimetric Projection: All three axes appear unequally foreshortened.

Oblique Projection

• Oblique projection is a type of parallel pictorial projection where projectors are parallel but not perpendicular to the picture plane.
• It is of two types:
  1. Cavalier Projection: Dimensions along all axes are plotted in full scale.
  2. Cabinet Projection: Dimensions along the diagonal axis are reduced to half of the actual value, while dimensions along other axes are plotted in full scale.

Perspective Projection

• Perspective projection is a type of pictorial projection where projectors are not parallel and converge to a point, mimicking the human eye's view.
• It is not used for working drawings but is useful for describing the natural view of an object to non-technical persons.
• There are three types of perspective projection: one-point (parallel), two-point (angular), and three-point (oblique).

Projection Methods

• The principal projection planes and quadrants used to create drawings are:
  • Frontal Plane (Vertical Plane): Front view is drawn here.
  • Horizontal Plane: Top view is drawn here.
  • Profile Plane: Side views are drawn here.
• There are two methods of projection:
  1. First Angle Projection: The object is placed in the first quadrant, and the top view is drawn below the front view.
  2. Third Angle Projection: The object is placed in the third quadrant, and the top view is drawn above the front view.

Orthographic Projection

• Orthographic projection is a way of drawing a 3D object from different directions, usually showing front, side, and plan views.
• It is useful for designs that are almost ready for manufacturing.
• The planes of projection are:
  • Vertical Plane (VP): Front view is drawn here.
  • Horizontal Plane (HP): Top view is drawn here.
• The intersection of these planes forms four quadrants, and the object can be placed in any one of them.

First Angle Projection

• In first angle projection, the object is placed in the first quadrant, and the top view is drawn below the front view.

Third Angle Projection

• In third angle projection, the object is placed in the third quadrant, and the top view is drawn above the front view.

Reference Line

• The reference line (xy) represents both the horizontal plane (HP) and the vertical plane (VP) when projections are drawn in their correct relationship.

Working Drawings

Working drawings, also called production drawings, are complete sets of drawings that detail the manufacturing and assembly of products and structures. They are widely used as orthographic views of machine parts, structures, and their assemblies.

Elements of Working Drawings

• Size and shape of the component.
• Format of the drawing sheet.
• Process sheet.
• Projection method.
• Limits, fits, and tolerances of size, form, and position.
• Material specification and shape (e.g., casting, forging, plates, rounds).
• Conventions used to represent certain components.
• Inspection and testing methods.
• Specification of standard components.

Applications of Working Drawings

• Physical Construction/Production: Used to construct or produce any structure or product.
• Permission: Required for residential construction permits.
• Estimation and Costing: Used by bidders and subcontractors to calculate materials, labor, and expenses.
• Permanent Record: Constitutes a permanent record of construction and design.
• Legal Record: Used as a basis for determining facts in legal issues during or after construction.

Construction Detailing in Plan and Section

Detail and section views provide specific information about construction or design features. They include wall sections and unique design details to ensure compliance with structural, material, and energy efficiency requirements.

Site Plans

A site plan is a large-scale drawing showing the full extent of a site for an existing or proposed development. It includes building footprints, travel-ways, parking, drainage, sanitary sewer lines, water lines, trails, lighting, and landscaping.

• Typically drawn at a scale of 1:500 or 1:200.
• Includes title block, directional orientation, key dimensions, materials, site boundaries, and surrounding features.

Preliminary Drawings

Preliminary drawings are initial project plans prepared by designers, architects, and engineers to convey concepts, designs, and ideas. They are used for exploring design concepts, material selection, preliminary cost estimates, and customer approval.

Topographic Maps/Drawings

Topographic maps indicate the main physical and geographical features of an area. They show buildings, fences, roads, rivers, lakes, forests, and changes in elevation using contour lines.

Suitability of Scales

• Topographic Maps: 1:50,000 to 1:250,000.
• Town Surveys: 1:5,000 to 1:50,000.
• Sketch Drawing: 1:100 to 1:500.
• Large Scale Survey and Layout: 1:500 to 1:2,000.
• Working Drawings: 1:50 to 1:200.

Structural Working Drawings

Structural drawings provide the shape and position of all parts of a structure, enabling smooth construction. They include plans, sections, elevations, dimensions, and reinforcement details.

Techniques of Freehand Drawing

Freehand sketches are used to outline basic ideas and concepts. They are drawn without measuring instruments and are essential for communication in engineering.

• Use soft lead pencils (2H for light lines, 2B or B for contours).
• Draw horizontal, vertical, and oblique lines with equal spacing.
• Circles and arcs are drawn last.

Building Drawing

Building drawings are essential for construction and must comply with local building codes. They include site plans, line plans, detailed plans, foundation plans, landscape plans, elevations, sectional elevations, perspective drawings, and submission drawings.

Types of Building Drawings

• Site Plan: Shows the location of the building, plot dimensions, and surrounding features.
• Line Plan: Represents internal room dimensions with single lines.
• Detailed Plan: Shows room sizes, arrangements, and wall thicknesses.
• Foundation Plan: Details the foundation layout.
• Elevation: Vertical views of the building (front, side).
• Sectional Elevation: Internal details shown by cutting the building.
• Perspective Drawing: True picture of the building for non-technical understanding.
• Submission Drawing: Prepared for approval by local authorities.