Projection Of Points 5gt1b

PROJECTION OF POINTS ENGINEERING DRAWING

INTRODUCTION :• An object is represented by drawing the boundaries of all the surfaces of the object. • The boundary of a surface may be made up of straight lines or curved lines or both. As each curve or straight line is logically made up of number of points, the theory of orthographic projections starts with projection of points.

Reference Line ‘XY’

ORTHOGRAPHIC PROJECTION – TOP VIEW AND BOTTOM VIEW

When planes of projection are extended beyond their line of intersection, they form FOUR QUADRANTS

ORTHOGRAPHIC PROJECTION – FRONT, TOP AND SIDE VIEW

FIRST ANGLE PROJECTION :• When the object is situated in First Quadrant, i.e. in front of V.P. and above H.P., then the projections on these planes obtained are called “First Angle Projection”. • The front view is drawn above ‘XY’ plane and the top view, below ‘XY’ plane. • In front view, H.P coincides with XY plane and in top view, V.P coincides with XY plane.

• Third Angle Projection :- The object is situated in 3rd Quadrant. The front view comes below XY plane, and top view above XY plane. • BIS recommends the use of first angle projections in line with ISO specifications all around the world. • Positions of points in space:-

NOTATIONS TO BE FOLLOWED :1. Actual points in space are to be denoted by capital letters i.e. A,B,C . 2. Their front views are denoted by corresponding lower case letters with dashes a’,b’,c’ and their top views by a,b,c 3. Projectors are drawn as continuous thin lines.

Example for a First Angle Projection :-

Classwork to do :-

1.

Four points in a plane are in such a way that, Point A is 20 above H.P and 30 in front of V.P, Point B is 20 above H.P and 30 behind V.P , Point C is 20 below H.P and 30 behind V.P , Point D is 20 below H.P and 30 in front of V.P. Draw the projections for each of the points on reference line XY.

2. A point P is 20 above H.P, 25 in front of V.P, and 30 in front of P.P (Profile Plane). Draw the front, top and side views of the point. 3. A point A is 15 above H.P and 20 in front of V.P. Another point B is 25 behind H.P and 40 below V.P. Draw the projections of A and B, keeping the distance between projectors equal to 90 . Draw the straight lines ing top views and front views

Classwork to do :4.

A point at 25 above the reference plane xy is in the front view of two points A and B. The top view of A is 40 behind V.P and the top view of B is 50 in front of V.P.

Draw the projections of the points and state their positions relative to the planes of projection and the quadrants in which they lie. 5. A point A is 20 above H.P and is in first quadrant. Its shortest distance from the reference line XY is 40. Draw the projections of the point and determine the distance from V.P.