Fishing Craft Technology

Practical 4 - Projection of planes

Projection of planes (Type I)

Plane Figures:
Plane figures or surfaces have only two dimensions viz. length and breadth, with negligible thickness.

Traces of Planes:
A plane, extended if necessary will meet the reference planes in line, unless it is parallel to any one of them. These lines are called as “traces of the plane surface”. The line in which the plane meets the H.P. is called as “Horizontal Trace” or H.T. of the plane. The line in which it meets the V.P. is called as its “Vertical Traces” or the V.T. In projection, the position of plane may be divided into two main types

• Perpendicular planes
• Oblique planes

Perpendicular planes can be classified into following sub groups.

• Perpendicular to two reference planes.
• Perpendicular to one plane and parallel to the other.
• Perpendicular to one plane and inclined to the other.

The planes which are inclined to both the reference planes are called as “Oblique planes”.

The plane perpendicular to both H.P. and V.P.

A plane perpendicular to horizontal and vertical reference planes, then its H.T. and V.T. are in a straight line, perpendicular to XY. The elevation and plan of the plane are both line, coinciding with V.T. and H.T. respectively.

• An equilateral triangle of 5 cm side has its V.T. parallel to and 3 cm above XY. It has no H.T. Draw its projections when one of its side is inclined 45° to the V.P.
  

• A regular pentagon of 4 cm side, parallel to and 4 cm above H.P. one of its side is parallel to V.P. draw its projection.
• A square ABCD of 4 cm side has a corner in the H.P. and 3 cm in front of V.P. All the sides of the square are equally inclined to the H.P. and parallel to the V.P. Draw its projection and show its traces.

• A regular hexagon of 4 cm side length has a side in the H.P. and 4 cm in front of the V.P. The plane is parallel to the V.P. Draw its projection.
• A regular pentagon of 3 cm side has one side in the H.P. Its plane is inclined at 450 to the H.P. and perpendicular to V.P. Draw itsprojection and traces.

Projection of planes (Type II)

• Draw the projections of a circle of 5 cm diameter having its plane vertical and inclined at 300 to the V.P. Its centre is 4 cm above the H.P. and 4 cm in front of the V.P.

• A square ABCD has its diagonal AC inclined at 300 to the H.P. and the diagonal BD inclined at 450 to the V.P. and parallel to the H.P. Draw its projection.

• Draw the projections of a regular hexagon having one of its sides in the H.P. and inclined at 600 to the V.P. and its surface making an angle of 450 with the H.P.
• A regular pentagon of 4 cm side has one corner in the H.P. Its plane is inclined at 300 to the H.P. and perpendicular to the V.P. Draw its projection.