1. ISOMETRIC PROJECTION Part II
Prof.T.JEYAPOOVAN
Department of Mechanical Engineering
Hindustan Institute of Technology and Science Chennai , India

2. Isometric Projection and Isometric Scale
Isometric projection is always used for combination of solids.
To draw isometric projection, isometric dimensions are used which is 0.82× True length.
A conversion scale used for converting true dimensions into isometric dimensions is shown in fig.

3. Draw TV and FV of the frustum of cone using isometric scale.
Example1: Draw the isometric projection of a frustum of a cone of base diameter 60 mm, top base diameter 35 mm and axis length 50 mm rests on HP on its base.
Draw TV and FV of the frustum of cone using isometric scale.
A square box of exact size is used in TV to enclose the frustum and construct the box in isometric.
Use 4-centre method to draw bottom base in isometric.
Draw another square to enclose top base of frustum in TV and locate it in isometric as shown.
Repeat the 4-centre method to complete top base in isometric.
Draw extreme generators and darken visible portion of the solid to complete isometric projection.

4. Draw the TV and FV of the prism using isometric scale.
Example 2: Draw the isometric projection of a hexagonal prism of side of base 40 mm and height 60 mm with a right circular cone of base 40 mm as diameter and altitude 50 mm, resting on its top such that the axes of both solids are collinear.
Draw the TV and FV of the prism using isometric scale.
A rectangular box of exact size is used to enclose the prism.
Construct the box in isometric.
Measure the corners from TV and mark them on the sides of the box.
Repeat the procedure for cone but construct it above the prism.
Darken the top, left and right edges of the prism and the visible portion of the objects to complete the isometric projection.

5. Draw the TV and FV of the cylinder using isometric scale.
Example 3: A square pyramid having a side of 50 mm base and 75 mm as axis height stands centrally on circular block of 100 mm diameter and 50 mm thick. The base edges of the pyramid are parallel to VP. Draw the isometric projection of the two objects.
Draw the TV and FV of the cylinder using isometric scale.
A square box of exact size is used to enclose the cylinder.
Construct the box in isometric.
Use 4-centre method to draw top base in isometric and repeat the same procedure for bottom base.
Repeat the procedure for square pyramid but construct it above the cylinder.
Darken the visible portion of the cylinder and square pyramid to complete isometric projection.

6. Draw the TV and FV of the cube using isometric scale.
Example 4: A sphere of diameter 40 mm rests centrally on top of a cube of side 50 mm. Draw the isometric projection of the solids.
Draw the TV and FV of the cube using isometric scale.
Construct the cube in isometric which is of same size as the box.
Note that isometric projection of a sphere is a circle of true diameter.
Mark the centre of the circle above the top face of cube at a height of 0.82 × radius. Then draw the circle with this centre with TRUE radius.
Darken the circle and visible portion of the cube to complete isometric projection.

7. Tips to draw Isometric Projection
To draw isometric projection, the top and front views are always drawn in isometric dimensions which will be used to construct the isometric projection.
Always isometric dimensions are used to draw the isometric drawing of combination of solids involving sphere or spherical shape.
Isometric projection of a sphere is always a circle of TRUE radius/diameter.
In isometric projection, importance is given to the 3D picture of the objects, so marking, dimensioning and hidden lines may be omitted.
Complete the isometric drawing by clearly drawing dark lines for the visible portion of the objects.

8. REFERENCE BOOKS
Jeyapoovan T, “Lesson Plans for Engineering Graphics”, 2010, Vikas Publishing House Pvt Ltd, New Delhi.
Jeyapoovan T, “Engineering Drawing and Graphics”, 2011, Vikas Publishing House Pvt Ltd, New Delhi.

9. End of Lesson 12
Thank You