24th March 2020, Period 3, 9.30 to 10.20 am,Class XII, EG, Topic: Isometric Projection - 2

Isometric Projection - 2


Some basic Concepts.....contd.


1. What is a helping figure and why is it needed?

a). You have learnt yesterday that when an Isometric Projection of an object is drawn, its dimensions suffers a reduction of approx. 18.5%. An object may have both, isometric as well as non-isometric edges (lines). Therefore, to help us in drawing the isometric projection on non-isometric edges, we need the help of a 'helping figure'.

b). A square and a rectangle do not have non-isometric edges, therefore these shapes (figures) do not need a 'helping figure' to draw their Isometric Projections. However, triangle, pentagon and a hexagon have non-isometric edges, hence we need a helping figure to draw their Isometric Projections.

2. What is another good use of a helping figure?

We use a helping figure to mark the centre of the base (or face) through which the solid axis passes.








3. What are the essentials of an Isometric Projection?

a). Direction of viewing : Any Isometric Projection should have the direction of viewing. It is marked by a small line with an arrowhead.

b). Proper dimensioning: We should mark dimensioning lines in a proper manner, unlike in orthographic projection. The dimension lines are drawn parallel to the three axes.   

c). Titles and Sub-titles: All projections, including Isometric Projections should mention the titles and subtiles (wherever necessary) that give the information about the object in question.

d). Proper lines: Axis, dimension

e). Hidden edges: of the object are not shown at all. No light lines and no dotted lines. 

Exercise 2: Isometric Projection of planar figures

Instructions:

a. Show direction of viewing, mark its centre and mention dimensions in all the above questions.
b. Solve these questions in your drawing file
c. Please take a picture of your answers (in one image) and post them in the EG Group.

Q 1. Draw the Isometric Projection of a pentagon of side 30 mm whose surface is parallel to the VP and one of its base edges parallel to the HP.

Q 2. Draw the Isometric Projection of a hexagon of side 40 mm whose surface is parallel to the HP and one of its base edges away from the observer parallel to the VP.

Q 3. Draw the Isometric Projection of a circle of diameter 50 mm whose surface is parallel to the VP.