Lecture 2: 2-D Transformation and Projection Multi-view Drawing PTT 105/3 Engineering Graphicss

PTT 105/3 Engineering Graphics Outline Projection Theory Multi-view Projection Principle views & View placement Projection angle Detail drawing: 1view, 2 view, 3 view drawing Creating multi-view drawing View Selection Line convention PTT 105/3 Engineering Graphicss

PTT 105/3 Engineering Graphics Projection Theory Engineering and technical graphics are depend on projection methods. Two methods commonly used: Parallel: object positioned at infinity & viewed from multiple points on an imaginary line, parallel to the object. Perspective: object positioned at finite distance & viewed from a single point. PTT 105/3 Engineering Graphicss

Parallel- all LOS are parallel Perspective- all LOS start at a point. Projection theory comprises of principles used to graphically represent 3D objects on 2D media based on 2 variables: Line of Sight (LOS): an imaginary ray of light between an observer’s eye and an object. Parallel- all LOS are parallel Perspective- all LOS start at a point. Plane of projection: an imaginary flat plane where the image created by LOS is projected. PTT 105/3 Engineering Graphicss

Orthographic Projection A parallel projection technique The projection plane is placed between observer and object. The projection plane is also perpendicular to the parallel line of sight. PTT 105/3 Engineering Graphicss

Multi-view projection Multi-view projection is an orthographic projection for which the object is behind the plane of projection. PTT 105/3 Engineering Graphicss

Multi-view drawings i. Employ multi-view projection technique ii. Generally 3 views of an object are drawn iii. Each view is a 2D flat image PTT 105/3 Engineering Graphicss

Example: Multi-view Projection PTT 105/3 Engineering Graphicss

Multi-view Lines PTT 105/3 Engineering Graphicss

Multi-view: Planes PTT 105/3 Engineering Graphicss

Multi-view: Planes PTT 105/3 Engineering Graphicss

Multi-view: 6 Principle Views The 6 principle views are the six mutually perpendicular views that are produced by six perpendicular planes of projection. Image an object is suspended in a glass box, the 6 sides become projection plane showing the six views. PTT 105/3 Engineering Graphicss

The views are laid flat by “unfolding the glass box” This forms the basis of two important multi-view drawing standard: Alignment of views Fold lines Top and bottom views are all aligned vertically & share the same height with dim. Rear, left, front and right side are aligned horizontally & share same height with dim. PTT 105/3 Engineering Graphicss

Fold lines are imaginary hinged edges of the glass box i. The fold line between the top & front views is labeled H/F ii. The distance from a point in front view to the H/F is the same as the distance from the corresponding point in the top view to the H/F fold line. PTT 105/3 Engineering Graphicss

View Placement PTT 105/3 Engineering Graphicss

View Placement The arrangement of views may vary as shown, where the top view is considered the central view. PTT 105/3 Engineering Graphicss

Angle Projection There are two standard arrangement of all six views of an object i. First-angle projection ii. Third-angle projection Each uses different symbol The names are derived from the method used to view the object being drawn PTT 105/3 Engineering Graphicss

In 1st angle projection, the object is placed in the first quadrant. In 3rd angle projection, the object is placed in third quadrant. PTT 105/3 Engineering Graphicss

Rules: Symbols 1st angle projection 3rd angle projection View from above is placed underneath View from above is placed above View from below is placed above View from below is placed below View from left is placed on right View from left is placed on left View from right is placed on left View from right is placed on right (a) 1st angle projection (b) 3rd angle projection PTT 105/3 Engineering Graphicss

Example: 1st and 3rd angle view projection PTT 105/3 Engineering Graphicss

1, 2 and 3 view drawing PTT 105/3 Engineering Graphicss

Step in creating multi-view drawing PTT 105/3 Engineering Graphicss

Before start drawing, produce sketch on rough paper i. Decide on front view and projection angle ii. Obtain the overall width, height and depth iii. Place the views (in block) iv. Determine approximate space between the views v. Sketch the component, place dimensions PTT 105/3 Engineering Graphicss

Creating 3-view drawing Draw border/frame, title block, etc. Draw border, title block Locating the view i. should be approx. in centre ii. distance between view = total length available – view length / 3 Drawing projection lines PTT 105/3 Engineering Graphicss

Creating 3-view drawing PTT 105/3 Engineering Graphicss

Creating 3-view drawing 2. Light construction of the views Draw light/thin horizontal & vertical lines accordingly for front view Draw center lines and hidden lines as final Draw top (or side) view Project top view (or side) from front view using thin, light construction line Draw side (or top) view Project side view (or top) from front view and top (or side) view All arcs and circles should be lined (final) at this stage PTT 105/3 Engineering Graphicss

Creating 3-view drawing 3. Lining in of the views To darken all visible edges (lines that represent a hard edge) Done using thick, black pencil (0.5mm, 2B) Should be done systematically for 3 views Start with horizontal line at the top of the top/plan view, working down the page using T-square From left hand side, working across the page, line in all vertical lines, using T-square and set square Projection lines may be left on the drawing if they are light PTT 105/3 Engineering Graphicss

Creating 3-view drawing 4. Write dimensioning, notes, annotation, etc. Be aware of redundant dimensioning 5. Complete drawing by writing the rest of title block, parts list & revision table, and others PTT 105/3 Engineering Graphicss

View Selection 4 basic decisions: 1. Determine the best position. The object must be positioned such a way that the surface of major features are either perpendicular or parallel to glass planes PTT 105/3 Engineering Graphicss

View Selection 2. Define the front view. Should show the object in natural state and show most features PTT 105/3 Engineering Graphicss

View Selection Determine the minimum number of views needed to completely describe the object. Determine other views that fewest number of hidden lines PTT 105/3 Engineering Graphicss

Line Convention PTT 105/3 Engineering Graphicss

Line Convention PTT 105/3 Engineering Graphicss

THANK YOU… PTT 105/3 Engineering Graphicss