Lesson Notes By Weeks and Term - Junior Secondary School 1

SECOND TERM E-LEARNING NOTE

SUBJECT:  BASIC TECHNOLOGY                                     

CLASS:  JSS 1

REFERENCE MATERIALS 

1. MELRVE, Basic science and technology for JSS, Book 1
2. NERDC, Basic Technology for JSS, Book 1

WEEK FIVE AND SIX        Date:……………………………

TOPIC:  FREEHAND SKETCHING

CONTENT

• Meaning of freehand sketching
• Sketching  a  straight line
• Sketching  a curve and a circle
• Sketching  a square and an irregular edge
• Definition of scale drawing
• Materials and instruments for scale drawing
• Types of scale drawing

DEFINTION OF FREEHAND SKETCHING

Freehand Sketching is one of the quickest methods by which the shape of an object can be communicated to others.  This is done by using a pen or pencil.

Architects think more of imaginary objects; they cannot take photographs but express this using freehand sketching.

Therefore, the knowledge of freehand sketching is of advantage. A good sketch reduces the task of writing needed to describe the object on the mind of the designer. The ability to make a freehand sketching is a valuable asset acquired through practice.

SKETCHING A STRAIGHT LINE

A straight line can be defined as the shortest distance between two points.

Straight line can be sketched following the procedures below:

1. Put a dash or dot far enough to the right-hand side of the paper.

• Start to draw a line from the left hand side to join the dash or dot with your eyes fixed on the point.

………………………………………..

EVALUATION

1. Define freehand sketching.
2. Describe how to sketch a straight line.

SKETCHING:  A CURVE AND CIRCLE

1. Curve: To draw a curve by freehand, it will be necessary to plot some points not too far from each other at different levels  like this :

With the points in position, attempt to draw curves to join them.

1. Circle: To draw circles, the easiest way is to draw lines which are equal in diameter to the circle in different directions. Each line must be drawn as faint as possible, with each crossing one another at a point, Now join the points by little curves from the tip of each line.

SKETCHING: A SQUARE AND AN IRREGULAR EDGE

This can be sketched in isometric or oblique view.Isometric view is at 300 to the  horizontal the at both sides .Oblique view is at 450 to the horizontal at one side

EVALUATION

1. Describe how to sketch a curve and a circle.
2. Describe how to sketch a square and an irregular edge.

DEFINITION OF SCALE DRAWING

Scale drawing can be defined as the accurate representation of objects in a determined proportion.Scale drawing is different from ordinary drawing in that it presents the object either reduced or enlarged. There are scales for reduction and for enlargement of the size of the object.

MATERIALS AND INSTRUMENTS FOR SCALE DRAWING

1. Metric rule

This has two flat straight edges. It is usually 30cm long. Each main division on the metric rule is equal to one centimeter (1cm =10mm) and each division is sub divided into 10 units being 1mm.Always start from 0 as the beginning of your measurement.

1. Scale rule

These have three straight edges and are triangular in shape. Each edge is graduated and each scale designation is marked on the rule.

EVALUATION

1. Define scale drawing

2. State the materials and instruments for scale drawing

SCALE

Some objects are too big for the actual size to be contained on a drawing paper, while some are too small for the parts to be clearly seen. Hence, such objects should be drawn to an appropriate scale.

Scale is usually given as a ratio and they are stated in the title block.

TYPES OF SCALE DRAWING

A scale is used to draw or read a scale on a drawing paper

We have the following scales:

1. Full scale drawing
2. Reduced scale drawing
3. Enlarged scale drawing

FULL SCALE DRAWING

In this scale drawing, the object is drawn to the same size with the actual size. e.g.   1:1

REDUCED SCALE DRAWING

The actual size of the object is reduced in proportion to the drawing. Reduced scale drawing is used when the object is too big, examples include 1:2   ,  1:5   ,1:10  , 1:50   ,1:100

Therefore a cupboard of size 1800mm long drawn as 18mm has a reduced scale drawing of 1:100mm

ENLARGED SCLAE DRAWING

This is used when the object to be drawn   is too small to be clearly seen .Here, the actual size of the object is enlarged in the proportion to the drawing.

Examples include 2:1, 10:1, 100:1,

Drawing size        100:1            actual size

EVALUATION QUESTIONS

1. Define scale drawing.
2. Mention three (3) types of scale drawing.

READING ASSIGNMENT

Read on Scale Drawing from Introductory Technology (JSS1) by Evans.  Pages 19-20

WEEKEND ASSIGNMENT

1. _____  is one of the  quickest methods by which the shape of an object can be communicated to others.(a) Technical drawing (b) Freehand sketching (c)Scale drawing (d) Isometric drawing

1. _______ can be defined as the shortest distance between two points.(a) Straight line (b) Curve (c)Circle  (d) Square
2. Isometric view is at ____ to horizontal at both sides  (a) 300 (b)450 (c) 600 (d) 900
3. Oblique drawing is at ____  to the horizontal at one  side  (a) 300 (b)450 (c) 600 (d) 900
4. The following are the advantages of free hand sketches except …………..
   1. A good sketch reduces the task of writing needed to describe the object on the mind of the designer. (b) The ability to make freehand sketching is a valuable asset to practice Engineering

work. (c) Laypersons can express themselves by freehand sketches. (d) Materials are wasted by freehand sketches.

6.________  can be defined as the accurate representation of objects in a determined proportion (a) Scale drawing (b) Freehand sketches (c) Technical drawing (d) Isometric drawing

7. In _____ scale drawing, the object is drawn to the same size with the actual size. e.g.   1:1 (a) enlarged (b) reduced (c) full (d) proportioned
8. In ______ scale drawing the actual size of the object is reduced in proportion to the  drawing .It is used when the object is too big , examples include 1:2   ,  1:5   ,1:10  , 1:50   ,1:100  (a) enlarged      (b) reduced       (c) full           (d) proportioned
9. In the scale expressed below 50 is the _____ of the object     50:1  . (a) actual size

(b) drawing size       (c) proportioned   (d) regular

10._____ scale drawing is used when the object to be drawn  is too small to be clearly seen (a) Enlarged  (b) Reduced (c) Full (d) Proportioned

THEORY

1. Define freehand sketching.
2. Describe how to sketch a straight line, curve and circle.
3. Define scale drawing.
4. a. State the materials and instruments for scale drawing.

1. Mention three (3) types of scale drawing.