JNTUH Engineering Drawing Study Materials

Engineering Drawing

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Traditional Drawing Tools

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DRAWING TOOLS

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DRAWING TOOLS

1. T-Square

2. Triangles

HB for thick line 2H for thin line

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DRAWING TOOLS

3. Adhesive Tape

4. Pencils

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DRAWING TOOLS

5. Sandpaper

6. Compass

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DRAWING TOOLS

7. Pencil Eraser

8. Erasing Shield

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DRAWING TOOLS

9. Circle Template

10. Tissue paper

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DRAWING TOOLS

11. Sharpener

12. Clean paper

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Freehand Sketching

Straight Line

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2. Spot the beginning and end points.

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1. Hold the pencil naturally.

3. Swing the pencil back and forth between the points, barely

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touching the paper until the direction is clearly established.

4. Draw the line firmly with a free and easy wrist-and-arm

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motion

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Horizontal line

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Vertical line

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Nearly vertical inclined line

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Nearly horizontal inclined line

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Method 1 : Starting with a square

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Small Circle

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1. Lightly sketching the square and marking the mid-points.

2. Draw light diagonals and mark the estimated radius.

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3. Draw the circle through the eight points.

Step 2

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Step 1

Step 3

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Method 2 : Starting with center line

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Small Circle

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1. Lightly draw a center line.

2. Add light radial lines and mark the estimated radius.

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3. Sketch the full circle.

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Step 2

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Step 1

Step 3

Arc

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Method 1 : Starting with a square

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Method 2 : Starting with a center line

Horizontal

Curved

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Slanted

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Straight

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Basic Strokes

Examples : Application of basic stroke “A” letter 1

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“I” letter

“B” letter 1

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Upper-case Strokes letters & Sequence Numerals Suggested

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Straight line letters

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Curved line letters & Numerals

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Curved line letters

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Lower-case letters Suggested Strokes Sequence

letter.

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The text’ s body height is about 2/3 the height of a capital

Example : Good and Poor Lettering

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GOOD

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Not uniform in style.

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Not uniform in height.

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Not uniformly vertical or inclined.

Not uniform in thickness of stroke.

Area between letters not uniform.

Area between words not uniform.

Sentence Composition

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Leave the space between words equal to the space requires for writing a letter “O”.

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Example

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ALLODIMENSIONSOAREOIN MILLIMETERSOUNLESS OTHERWISEOSPECIFIED.

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GRAPHICS LANGUAGE

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1. Try to write a description of this object.

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Effectiveness of Graphics Language

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2. Test your written description by having someone attempt to make a sketch from your description.

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You can easily understand that ‌

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The word languages are inadequate for describing the size, shape and features completely as well as concisely.

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Composition of Graphic Language

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edges and contours of objects.

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Graphic language use lines to represent the surfaces,

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The language is known as “drawing” or “drafting” .

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A drawing can be done using freehand, instruments or computer methods.

Freehand drawing

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The lines are sketched without using instruments other than pencils and erasers.

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Example

Instrument drawing

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Instruments are used to draw straight lines, circles, and curves concisely and accurately. Thus, the drawings are usually made to scale.

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Example

Computer drawing

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such as AutoCAD, solid works etc.

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The drawings are usually made by commercial software

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Example

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Architectural Graphics

Elements

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Drawing comprises of graphics language

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Word language

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Describe a shape (mainly).

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Graphics language

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and word language.

Describe size, location and specification of the object.

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Basic Knowledge for Drafting

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Word language

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Geometric construction

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Projection method

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Line types

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Graphics language

Lettering

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PROJECTION METHOD

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PROJECTION METHOD

Perspective

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Parallel Orthographic

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Oblique

Axonometric

Multiview

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PROJECTION THEORY

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The projection theory is used to graphically represent

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3-D objects on 2-D media (paper, computer screen).

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The projection theory is based on two variables: 1) Line of sight

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2) Plane of projection (image plane or picture plane)

Line of sight

is an imaginary ray of light between an

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observer’s eye and an object.

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There are 2 types of LOS : parallel and converge

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Line of sight

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Parallel projection

Perspective projection

Line of sight

Plane of projection is an imaginary flat plane which

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the image is created.

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The image is produced by connecting the points where

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the LOS pierce the projection plane.

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Plane of projection

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Parallel projection

Perspective projection Plane of projection

1) It is difficult to create.

2) It does not reveal exact

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shape and size.

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Disadvantage of Perspective Projection

Width is distorted

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Orthographic Projection

MEANING

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Orthographic projection is a parallel projection technique

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in which the parallel lines of sight are perpendicular to the

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projection plane

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Object views from top

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3 4 Projection plane

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ORTHOGRAPHIC VIEW

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Orthographic view depends on relative position of the object

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to the line of sight.

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More than one view is needed to represent the object.

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Two dimensions of an object is shown.

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Multiview drawing

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Three dimensions of an object is shown.

Axonometric drawing

Rotate

Tilt

ORTHOGRAPHIC VIEW

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Orthographic projection technique can produce either

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1. Multiview drawing that each view show an object in two dimensions.

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2. Axonometric drawing that show all three dimensions of an object in one view.

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Both drawing types are used in technical drawing for

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communication.

Axonometric (Isometric) Drawing Easy to understand

Disadvantage

Shape and angle distortion

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Distortions of shape and size in isometric drawing

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Circular hole becomes ellipse.

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Example

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Advantage

Right angle becomes obtuse angle.

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Types of Axonometrics

Multiview Drawing

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It represents accurate shape and size.

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Advantage

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Multiviews drawing (2-view drawing)

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Example

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Disadvantage Require practice in writing and reading.

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The Glass Box Approach

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Orthographic Projection

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Opening the Box

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Final Views

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Six Orthographic Views

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Laying Out All Six Views

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Three Primary Views

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Construction of Views

Third-angle Projection

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First and Third Angle Projections

First-angle Projection

• First Angle – International • Third Angle – U.S.

Basic Line Types

Continuous thick line

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Dash thick line

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Continuous thin line

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Chain thin line

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Name according to application

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Appearance

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Types of Lines

Visible line Dimension line Extension line Leader line Hidden line Center line

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Meaning of Lines

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current view

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Visible lines represent features that can be seen in the Hidden lines represent features that can not be seen in

represents symmetry, path of motion, centers

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Center line

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the current view

of circles, axis of axisymmetrical parts

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Dimension and Extension lines indicate the sizes and

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location of features on a drawing

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Example : Line conventions in engineering drawing

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Good practice

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Exercise

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• Complete three orthographic views of the object shown on the next slide.

• Include visible, hidden, and center lines where appropriate.

• You will be given 7 minutes.

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Object for exercise

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Solution

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Drawing Standard

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Introduction

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drawings are represented.

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Standards are set of rules that govern how technical

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Drawing standards are used so that drawings convey

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the same meaning to everyone who reads them.

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Standard Code

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Full name

Code

USA

ANSI

American National Standard Institute

Japan

JIS

Japanese Industrial Standard

UK

BS

British Standard

Australia

AS

Australian Standard

Germany

DIN

Deutsches Institut fĂźr Normung

ISO

International Standards Organization

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Country

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Partial List of Drawing Standards Contents

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Code number

Sizes and Format of Drawings

JIS Z 8312

Line Conventions

JIS Z 8313

Lettering

JIS Z 8314

Scales

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JIS Z 8311

JIS Z 8316

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JIS Z 8317

Projection methods

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JIS Z 8315

Presentation of Views and Sections

Dimensioning

Drawing Sheet

Standard sheet size (JIS)

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210 x 297 297 x 420 420 x 594 594 x 841 841 x 1189

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A4 A3 A2 A1 A0

A2

(Dimensions in millimeters)

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A3

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A4

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Trimmed paper of a size A0 ~ A4.

A0

Orientation of drawing sheet 1. Type X (A0~A4)

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2. Type Y (A4 only)

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Drawing space

Drawing space

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Title block

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Sheet size A4 A3 A2 A1 A0

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Border lines

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c (min) d (min) 10 25 10 25 10 25 20 25 20 25

Title block

Length, size

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Drawing Scales

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Scale is the ratio of the linear dimension of an element

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of an object shown in the drawing to the real linear

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Size in drawing

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dimension of the same element of the object.

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Actual size

Drawing Scales

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Designation of a scale consists of the word “SCALE”

SCALE 1:1

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followed by the indication of its ratio, as follow for full size

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SCALE X:1 for enlargement scales

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SCALE 1:X for reduction scales