Textbook of Engineering Drawing, Second Edition

4.18 Textbook of Enginnering Drawing------------------

1. Draw the major (AB) and ninor (CD) axes and locate the centre O.


2. Locate the foci F I and F z by taking a radius equal to 60 mm (112 of AB) and cutting AB
   at F I P I and F z with C as the centre.


3. Mark a number of points 1,2,3 etc., between F I and 0, which need not be equi-distance.


4. With centres FI and Fz and radii Al and Bl respectively, draw arcs intersecting at the
   points PI and P;.


5. Again with centres F I and F 2 and radii Bland A 1 respectively, draw arcs intersecting at

the points QI and Q;.

6. Repeat the steps 4 and 5 with the remaining points 2,3,4 etc., and obtain additional points
   on the curve.
   Join the points by a smooth curve, forming the required ellipse.
   To mark a Tangent and Normal to the ellipse at any point, say M on it, join the foci F I and F 2
   with M and extend F zM to E and bisect the angle <EMF I' The bisector TT represents the required
   tangent and a line NN drawn through M and perpendicular to TT is the normal to the ellipse.


7. Oblong Method (Fig.4.27)

A

3'

2'

l'

l'

2'

3'

K

120

Fig. 4.27 Oblong Method

1. Draw the major and minor axes AB and CD and locate the centre O.


2. Draw the rectangle KLMN passing through A,D,B,C.


3. Divide AO and AN into same mumber of equal parts, say 4.


4. Join C with the points 1',2',3'.


5. JoinD with the points 1,2,3 and extend till they meet the lines C~, C~, C~ "respectively at
   PI' Pz and P 3 •