Page 23 - CITS - ED - Mechanical

ENGINEERING DRAWING - CITS

– parallelogram method
– offset method
Practical application: Search lights, reflecting surfaces for light and sound, bridge arches, wall brackets and
largely used in graphic methods for determining the stress upon beams and girders etc.

Parabolic curves

Follow the procedures given below and construct parabolic curves.

Procedure

Exercise 2.1

Construct a Parabola from a given focus is at 50 mm from the directrix. (Fig 1) - Ordinate method.
• Draw a vertical line D-D the directrix.
1
• Draw horizontal line XX , the axis through any point X on the directrix.
1
• Mark the focus 'F' on XX = 50 mm from X (on the directrix).
1
• Mark the mid point of XF, as V.

• Mark a number of points from V towards right side on the axis as 1,2,3,4.....
• Draw vertical lines through these points as shown, forming double ordinates.
• Point 'F' as centre, X-1 as radius, draw arcs on the co-ordinates (vertical lines) passing through 1, mark points
P & P .
1
1
1
• X-2 as radius, F as centre, draw arcs on the 2nd ordinate, mark P & P .
2
1
2
• Similarly get point P , P .... P , P etc. on the axis as above.
1
1
4
3
4
3
• Join all the points with a smooth curve, by free hand and form the parabola curve.
Fig 1

10
CITS :Engineering Drawing (Mechanical) - Exercise 2