# Lesson Notes By Weeks and Term - Junior Secondary School 3

ISOMETRIC DRAWING

TERM: FIRST TERM

SUBJECT: BASIC TECHNOLOGY

CLASS: JSS 3

REF MATERIALS

• EVANS BASIC TECH FOR JSS BOOK 3
• NERDC BASIC TECH FOR JSS BOOK THREE

WEEK SIX

TOPIC: ISOMETRIC DRAWING.

CONTENT

1. Meaning Of Isometric Drawing
2. Angles Of Projection
3. Differences Between Isometric Drawing And Isometric Projection
4. Uses of isometric drawing
5. Making Isometric Projection

ISOMETRIC DRAWING

This is a clear way of presenting information about the physical outlook of objects.

One method of pictorial representation of objects is isometric drawing. Isometric means “equal measures”. It shows the three faces of an object. It indicates the length, width and height. In this manner the shape can be easily understood.

ANGLES OF PROJECTION

Isometric drawing is the pictorial method of drawing an object in which all its isometric axes are projected 300 to the horizontal and 1200 to one another.

Any line parallel to any of three lines or isometric axes is known as an isometric line

EVALUATION

1. Define isometric drawing
2. At what angle is isometric drawing projected?

IMPORTANCE OF ISOMETRIC DRAWING

1. It helps us to develop the ability to draw every object to appear look like photograph
2. It also helps the designer to put down ideas easily before going into the detailed description of various parts of the system.
3. It is used for explaining the true shapes of objects to technical and non-technical people

SOLID SHAPES

The following objects can be drawn in isometric drawing: a block, a hammer, a prism, a pyramid, truncated objects, a cone, right objects, regular polygons.

DIFFERENCES BETWEEN ISOMETRIC DRAWING AND ISOMETRIC PROJECTION

Isometric drawing is the drawing in which the full dimension is achieved as this is normally marked. The scale is 100:100.

Isometric projection is the fore-shortened size of an object. The scale is 81: 100

Whereas an isometric drawing is drawn with an ordinary scale, an isometric projection is drawn with an isometric scale which makes the look shorter (foreshortened) than the real size.

MAKING ISOMETRIC PROJECTION

1. Draw a horizontal line.
2. At a point A on the line, erect line AC
3. On the left side of A, use the 300 set squares to draw line AD. Do the same for line AB on the right side of A.
4. At point B, erect line BE and at point D erect line DG.
5. At point C, draw CE parallel to AB and CG parallel to AD.
6. Draw GF parallel to CE and EF parallel to GC.

USES OF ISOMETRIC DRAWING

Isometric drawings are used to:

1. Promote quick and easy understanding of the shape and size of an object.
2. Make quick design and construction of objects.
3. Give a more realistic impression of the form of an object than by orthographic drawing.
4. Produce catalogues, leaflets and manuals by artists.

EVALUATION

1. State the importance of isometric drawing
2. Draw a cube of 60mm in isometric drawing

PROJECT

1. Construct a DODECAGON using cardboard made up of 12 regular pentagons of 50mm length.

GENRALEVALUATION

1. Define Isometric drawing
2. Draw the following shapes (a) right rectangular pyramid (b) oblique pentagonal pyramid
3. Measure the length, width and height of your mathematical set and produce a reduced scale of it.
4. Differentiate between isometric projection and isometric drawing.

OBLQUE DRAWING AND PERSPECTIVE DRAWING

REFERENCE MATERIALS

1. EVANS- INTRODUCTORY TECHNOLOGY BOOK 3, pages 8-12.
2. NERDC, BASIC TECHNOLOGY,BOOK 3 pages 42-47.

WEEKEND ASSIGNMENT

1. Which of the following is the foreshortened size of an object? A. Isometric projection B. isometric drawing  C. projector line D. identification line.
2. In isometric drawing, objects are always drawn at ____ angle to the horizontal (a) 600 (b) 300 (c) 1200 (d) 400.
3. A polygon with 12 sides is called ____A. Nonagon B. Dodecagon C. Decagon  D. Pentagon
4. A pyramid is right if its ____ coincides with the axis A. pyramid B. altitude C. vertex
1. oblique.
1. Which of the following depict pictorial method of drawing objects? A. scale drawing
1. perspective drawing  C. isometric drawing D. oblique drawing.

THEORY

1. State the differences between Isometric drawing and Isometric projection.
2. Construct a cube of 70mm in an isometric drawing.