Textbook of Engineering Drawing, Second Edition

_____ Geometrical Contructions 4.17

Other Methods of Construction of Ellipse

Given the dimensions of major and minor axes the ellipse can be drawn by, (i) Foci method,
(ii) Oblong method, (iii) Concentric circle method and (iv) Trammel method.

To draw an ellipse with major and minor axes equal to 120 mm and 80 mm respectively.

Definition of Ellipse (Fig.4.25)

Ellipse is a curve traced by a point moving such that the sum of its distances from the two fIxed
points, foci, is constant and equal to the major axis.

c

A 8

Fig. 4.25 Properties of an Ellipse

Referring Fig.4.25, FI, and F2 are the two foci, AB is the major axis and CD is the minor axis.

As per the difmition, PF I + PF 2 = CF I + CF 2 = QF I + QF 2 = AB. It may also be noted that CF I =

CF 2 = 112 AB (Major axis)

Construction

1. Foci Method (Fig.4.26)

E

T

A B

120

Fig. 4.26 Construction of Ellipse - Foci Method