INTRODUCTIONTO

ENGINEERING GRAPHICS

Drawing Instrument

Typical Drawing Equipment

Objectives in Drawing

1. Accuracy

2. Speed

3. Legibility

4. Neatness

Drawing Boards

The left edge and right edge of a drawing board has a true straight edge.

For right-handed people, the left-hand edge of the board is called the working edge because the T-square head slides against it.

For left-handed people, the right-hand edge of the board is called the working edge because the T-square head slides against it.

T-Squares

The T-square is made of a long strip called the blade, fastened at right angles to a shorter piece called the head.

The drawing paper should be placed close to the working edge of the board to reduce any error resulting from the bending of the blade of the T-square.

The paper should also be placed close enough to the upper edge of the board to permit space at the bottom of the sheet for using the T-square.

Drafting tape is used to fasten the drawing paper to the drawing board.

Drawing Pencils

High-quality drawing pencils should be used in technical drawing, never ordinary writing pencils.

Many makes of mechanical pencils are available together with refill leads in all grades. Choose a mechanical pencil that feels comfortable in your hand.

HARD MEDIUM SOFT

9H 8H 7H 6H 5H 4H 3H 2H H F HB B 2B 3B 4B 5B 6B 7B

Hard leads are used where extreme accuracy is required. Generally these leads are used for construction lines.

Medium leads are used for general purpose line work in technical drawing.

Soft leads are used for various kinds of art work. These leads are too soft to be useful in mechanical drafting.

Drawing Leads

The first consideration in the selection of a grade of lead is the type of line work required. For light construction lines and guide lines for lettering use a hard lead. For all other line work, the lines should be BLACK. The lead chosen should be soft enough to produce jet black lines but hard enough not to smudge.

TASK LEAD GRADE LINE WEIGHTCONSTRUCTION LINES 3H, 4H, 6H THIN, LIGHT

VISIBLE OBJECT LINES H, F, HB THICK, DARK

HIDDEN LINES 2H, H THIN, DARK

CENTER LINES 2H, H THIN, DARK

DIMENSION LINES 2H, H THIN, DARK

EXTENSION LINES 2H, H THIN, DARK

LEADER LINES 2H, H THIN, DARK

CUTTING PLANE LINES H, F, HB THICK, DARK

PHANTOM LINES 2H, H THIN, DARK

LETTERING H, F, HB THIN, DARK

Drawing Lead Applications

Drawing Horizontal and Vertical Lines

To draw a horizontal line, press the head of the T-square against the working edge of the board with your left hand. Lean the pencil in the direction of the line at an angle of approximately 60º and draw the line from left to right. While drawing the line, rotate the pencil to distribute the wear uniformly on the lead to maintain a symmetrical point.

To draw a vertical line, press the head of the T-square against the working edge of the board with your left hand and place a triangle against the blade of the T-square. Lean the pencil in the direction of the line at an angle of approximately 60º and draw the line upward, rotating the pencil to distribute the wear uniformly on the lead to maintain a symmetrical point.

TrianglesMost inclined lines are drawn at standard angles using the 45º x 45º triangle and the 30º x 60º triangle.

In addition to drawing angles of 90º, 45º, 30º, and 60º, triangles can be combined to draw angles of 15º increments.

ScalesScales are instruments used in making technical drawings full size or at a given reduction or enlargement.

Types of scales include metric scales, engineers’ scales, decimal scales, mechanical engineers’ scales, and architects’ scales.

Scales are usually made of plastic or boxwood and are either triangular of flat in shape.

Giant Bow Sets

Giant bow sets contain various combinations of instruments.

Giant Bow Compass

The giant (large) bow compass has a center wheel and can be adjusted simply by opening or closing the legs of the compass while turning the center wheel.

Using a Giant Bow Compass

1. Set off the required radius on one of the center lines.

2. Place the needle point at the exact intersection of the center lines.

3. Adjust the compass to the required radius

4. Lean the compass in the direction that you are going to draw the circle. Draw the circle in a clockwise direction while rotating the handle between the thumb and forefinger.

Sharpening the compass lead

A properly sharpened compass point is formed by rubbing the lead on the sandpaper pad.

A properly sharpened compass point consists of a single elliptical face.

A properly adjusted compass

The needlepoint extends about halfway into the paper when the

lead touches the paper.

Tee Square

Irregular / French Curves

SET SQUARES

DRAWING INSTRUMENTS •Layout of a Drawing Sheet

Typical Sheet Sizes and Borders

A Series Formats (mm)

A0 841 × 1189A1 594 × 841A2 420 × 594A3 297 × 420A4 210 × 297A5 148 × 210A6 105 × 148A7 74 × 105

DRAWING INSTRUMENTS 2. Drawing Sheets

STANDARD SHEETS

TITLE BLOCK

ESSENTIAL REQUIREMENTS FOR TITLE BLOCK

1. NAME OF THE FIRM2. TITLE OF THE DRAWING3. MATERIAL TO BE USED4. SYMBOL – FIRST ANGLE OR THIRD ANGLE5. NUMBER OF SHEETS PERTAINING TO DRAWING6. DRAWN BY7. CHECKED BY8. APPROVED BY9. DATE OF RELEASE10. DRAWING NO.11. SCALEOTHER INFORMATIONS, IF REQUIRED1. TYPE OF TREATMENT2. FINISH/COATING3. STOCK SIZE4. NO. OFF

Engineering Drawing

Lettering

- Size (or text height)- line thickness

- Shape- Space between letters- Space between words

Recommendation

LegibilityLegibility

UniformityUniformity

Text’s style on the drawingmust have the following2 properties

Examples

GOOD

Not uniform in style.Not uniform in height.

Not uniformly vertical.Not uniform inthickness of stroke.Inappropriate spacebetween letters

Style (this course)

Gothic vertical style.

Begin the sentence, phrase or word with a capital letter.

Text height 2~3 mm.

Space between lines of text is about of text height.

Height of the lower-case letter is about 2/3 of that of a

capital letter.

Basic Strokes

Straight Slanted CurvedHorizontal

1 1 2

3

“I” letter “A” letter

1

2

3

4 5

6

“B” letter

Examples

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

Example

Sentence Composition

ALL DIMENSIONS ARE INMILLIMETERS

O O OO UNLESS

OTHERWISE SPECIFIED.O

Engineering Drawing

Line Types

Basic Line Types &Application

ContinuousDashChain

Style

Thickness Thick Thin 1. Dimension line2. Extension line3. Leader line

Center line

Hidden line

Visible line

represent features that can be seen in the current view.

represent features that can not be seen in the current view.

represents symmetry, path of motion, centers of circles,

axis of axisymmetrical parts

indicate the sizes and location of features.

1. Visible line

3. Hidden line

4. Center line

2. Dimension line Extension line Leader line

Basic Line Types An Example

Basic Line Types