TA 101: Technical Arts 2015-16 II Dr. Prishati Raychowdhury Department of Civil Engineering IIT Kanpur Office: FB 336; Phone: 6692 E-mail: prishati@iitk.ac.in

Orthographic Projections Lecture 4 Orthographic Projections

Orthographic Projections: Review Orthographic projection is a 2D representation of a 3D object The projecting rays are perpendicular to the plane of projection The rays forming an image on the plane of projection are parallel to each other The observer is at infinity Principal views are obtained using three mutually perpendicular projection planes

Three important things about any projection: OBJECT, OBSERVER, PLANE of PROJECTION Case 1: OBJECT PLANE of PROJECTION OBSERVER Case 2: OBSERVER OBJECT PLANE of PROJECTION Case 1: Third Angle Projection Method Case 2: First Angle Projection Method

Third Angle Projection Projection plane is between object and observer (i.e., object is inside the glass box)

Top view Front view Side/Profile view

Third Angle Projection Top view Front view Right side view

First Angle Projection Object is between the observer and projecting plane (i.e., object is outside the glass box)

First Angle Projection

First Angle Projection Right Side View Front View Top View

First and Third angle Projection Front view RHS view Top view Front View RHS View Top View THIRD ANGLE PROJECTION FIRST ANGLE PROJECTION

First and Third angle Projection II III IV I LV I FV I TV III TV III FV Object in 1st quadrant : FIRST ANGLE PROJECTION Object in 3rd quadrant : THIRD ANGLE PROJECTION

First/Third angle Top view FIRST ANGLE PROJECTION THIRD ANGLE PROJECTION

First/Third angle Front view FIRST ANGLE PROJECTION THIRD ANGLE PROJECTION

Projection Systems United States and Europe: 3rd angle projection British Standards: 1st angle projection India: Formerly only 1st angle projection was in use, now BIS standard allows both In this course we will mainly use third angle projection system, unless mentioned otherwise However, you should be able to read both

Convention to indicate THIRD Angle Projection Symbol for THIRD Angle Projection System LHS View Front View

Convention to indicate FIRST Angle Projection Symbol for FIRST Angle Projection System Front View LHS View

Symbols for 1st/3rd Angle Projection are generally present in the Title block

Example Third Angle Projection First Angle Projection RIGHT VIEW FRONT VIEW TOP VIEW Third Angle Projection First Angle Projection

Another Example Viewing faces Top Face Back Face Right Side Face Left Face Bottom Face Front Face

Third Angle Projection Object behind plane Top View Top Front Right Front View Right Side View

First Angle Projection Object in front of plane Right Side View Front View Back Left Bottom Top View

Choosing right object orientation Example: Guided ramp

Example 2

Example 2

Example 2

Example 2

Object Orientation The simplest position is to be used Front view should get maximum details Reduce the number of hidden lines Principal faces are perpendicular to the sight directions (projection lines) and parallel to the projection planes

Selection of Views Select the least number of views required which will completely explain the object In some cases, one or two views are sufficient In most cases, three views will be sufficient For unsymmetrical objects, more than three views may be required

Spacing the Selected Views Necessary to utilize the space efficiently Do preliminary planning before actual drawing Projecting the Views Draw all the views concurrently DO NOT attempt to complete one view before proceeding to another You may require help from other views to complete a particular view

Order of Precedence of Lines Firm Object Line Hidden Object Line Center Line Projection Line/ Construction Line

Precedence of Lines

Hidden Lines Dashed Lighter than full lines Dashes of uniform length No space Join Dashes

Join dashes

Your Drawing Should Look Like This

Draw Views Concurrently α

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