Isometric Projection of a Sphere
This post explains the simple steps to draw the isometric projection of a sphere.
A Sphere is solid without any edges or vertex. 
It looks like a circle in any direction. 

Thus, it has only one point of contact when rested on a plane.
In an isometric projection, this point of contact is not visible. 
Let’s consider isometric projection of a sphere is to be drawn for a diameter of 60 mm.
Draw the principal axis OA and OB of length 60 mm inclined at 30° to the horizontal base line.
Complete the box, and draw the centre lines.
Draw the vertical axis of length which is equal to a radius of the sphere in an upright position from the centre point. 
That is 60/2 = 30 mm.
With P as a centre, draw a circle of radius as 30 mm. 
Thicken the circle line. 
Complete the isometric projection of a sphere with dimensioning and direction of viewing.

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