Engineering graphics Basic Construction_lec1.ppt

Lecture 1 Tuesday 15 April 2025 1
ENGINEERING GRAPHICS
1E9
Lecture 1: Introduction
Lecturer: Dr. Bidisha Ghosh (bghosh@tcd.ie)

Assessment
• Examination: 75% of the overall mark
– 3 sections (A, B and C)
– 2 questions per section
– 3 questions to be answered, one from each
section
• Dr B. Ghosh : Sections A and B
• Dr G. O’Donnell : Section C
• Labs 25% - assessed by coursework
– 10 % AutoCAD
– 10% D.O. Tutorials Dr B. Gosh
– 5 % D.O. Assignment Dr G. O’Donnell

Time Table
Lecture
Mon
10-11 a.m.
Drawing Office practicals
(AutoCAD laboratories for wks 11-12)
Mon 2-5 p.m. (group C)
Tues 2-5 p.m. (group D)
Wedn 2-5 p.m.( group A)
Fri 9 a.m.-12 noon (group B)
Semester 1
Wk 1
Mon 28th
Sept BG -
Wk 2 BG BG
Wk 3 BG BG
Wk 4 BG BG
Wk 5 Holiday -
Wk 6 GO’D GO’D
Wk 7 Reading wk Reading wk
Wk 8 GO’D GO’D
Wk 9 BG BG
Wk 10 SP -
Wk 11 SP SP
Wk 12 SP SP
BG - Hand drawing I- Dr Bidisha Gosh
GO’D - Hand drawing II- Dr Garret O’Donnell
SP - Autocad – Dr Sara Pavía
See JF timetable for venues

Syllabus – Hand Drawing 1
• Basic Construction
• Orthographic Projections
• Isometric Projections
• Auxiliary Views
• Perspective

Evaluation
• Examination (Sections A & B)
(2/3 of the total examination marks)
• Continuous Assessment
(10% of the total course marks)
– four drawing office tutorials

Aim of the Course
• Knowledge of engineering drawing
instruments
• Understanding and interpretation of
technical drawings
• Ability to develop projections of a 3D
object

Reference Books
• Technical Draughtsmanship
By Eanna O’Broin
• Engineering Drawing with Worked
Examples
By M.A. Parker & F. Pickup
• Technical Drawing
By F. E. Giesecke, A. Mitchell,
H. C. Spencer, I. L. Hill, J. T. Dygdon,
J. E. Novak

Waterfall
M. C. Escher
Technical
drawing is the
language of
engineers and
designers

Topics of Interest
•Drawing Instruments
•Lines
•Dimensioning
•Basic construction

1. Drawing Board
DRAWING INSTRUMENTS 1

A Series Formats
(mm)
A0 841 × 1189
A1 594 × 841
A2 420 × 594
A3 297 × 420
A4 210 × 297
A5 148 × 210
A6 105 × 148
A7 74 × 105
2. Drawing Sheets

•Layout of a Drawing Sheet

• Tee square/ Drafting Machine

• Set squares (a pair)

• Irregular/ French curves

• Compasses
• Divider
• Protractor
• Ruler/Scale
• Pencil, Eraser

TYPES OF LINES
• 3 Main Types
DRAWING LINES 1

• Lines to aid understanding
DRAWING LINES 2

DIMENSIONING 1
Dimension Lines (DL)
Position of DL

DIMENSIONING 2
Alignment of DL DL of Small Features
Dimensioning Angles Dimensioning Circles

DIMENSIONING 3

DIMENSIONING 4
Correct Practice of Dimensioning
Drawing should
only carry
dimensions needed
to manufacture

Drawing Parallel Lines
DRAWING LINES

Drawing Perpendicular Lines
DRAWING LINES

Bisection of A Line
1. Place your compass point on A and stretch the compass
MORE THAN half way to point B.
2. With this length, swing a large arc that will go BOTH
above and below segment AB.
3. Without changing the span on the compass, place the
compass point on B and swing the arc again. The new
arc should intersect the previous one above and below
the segment AB.
4. With your scale/ruler, connect the two points of
intersection with a straight line.
5. This new straight line bisects segment AB. Label the
point where the new line and AB cross as C.
6. Segment AB has now been bisected and AC = CB.
DRAWING LINES
A B

Divide A Line into Multiple Sections
1. From one end of the given line AB (say, A) draw a line AC
at a convenient angle
2. Using a scale/ruler divide the BC into the required number
of parts making them of any suitable length.
3. Join the last point on line AC (say, C) to B
4. Draw construction lines through the other points on the line
AB which are parallel to CB
DRAWING LINES

Bisection of An Angle
1. Place the point of the compass on the vertex of angle BAC
(point A).
2. Stretch the compass to any length so long as it stays ON the
angle.
3. Swing an arc with the pencil that crosses both sides of angle
ABC. This will create two intersection points (E and F) with
the sides of the angle.
4. Place the compass point on E, stretch your compass to a
sufficient length and draw another arc inside the angle - you
do not need to cross the sides of the angle.
5. Without changing the width of the compass, place the point of
the compass on F and make a similar arc. These two small
arcs in the interior of the angle should be crossing each other.
6. Connect the point of intersection of the two small arcs to the
vertex A of the angle with a straight line.
7.
DRAWING LINES

Find the Centre of an Arc
1. Select three points A, B and C on the arc and join AB and
BC
2. Bisect AB and BC.
3. Fine the intersection point of the bisecting lines/bisectors.
That is the centre of the arc.
DRAWING LINES

Inscribe a Circle in a Triangle
1. Bisect angle ABC and angle BAC.
2. Fine the intersection point of the bisecting lines/bisectors.
That is the centre of the circle.
3. The radius of the circle is the length of a perpendicular line
on any of the sides of the triangle drawn from the centre of
the circle.
DRAWING LINES

Circumscribe a Circle on a Triangle
1. Bisect sides AC and BC.
2. Fine the intersection
point of the bisecting
lines/bisectors. That is
the centre of the circle.
3. The radius of the circle is
the length of a line
joining any one of the
vertices of the triangle to
the centre of the circle.
DRAWING LINES

Notes for Tutorials
• The tutorials start next Monday in drawing office in
museum building
• Each tutorial is worth 2.5%
• Bring your own drawing instruments
• Drawing sheets will be provided
Students will not be allowed in the tutorial without
instruments

Engineering graphics Basic Construction_lec1.ppt

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