1 PTT 105/3 Engineering Graphicss. Projection Theory Multi-view Projection Principle views & View...

Lecture 2:2-D Transformation

and Projection

Multi-view Drawing

1PTT 105/3 Engineering Graphicss

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


Projection Theory

Engineering and technical graphics are depend on projection methods.

Two methods commonly used:a) Parallel: object positioned

at infinity & viewed from multiple points on an imaginary line, parallel to the object.

b) Perspective: object positioned at finite distance & viewed from a single point. 3PTT 105/3 Engineering Graphicss

Projection theory comprises of principles used to

graphically represent 3D objects on 2D media based on 2

variables:

i. 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.

ii. Plane of projection: an imaginary flat plane where

the image created by LOS is projected.


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.


Multi-view projection

Multi-view projection is an orthographic projection for which the object is behind the plane of projection.


Multi-view drawingsi. Employ multi-view projection techniqueii. Generally 3 views of an object are

drawniii. Each view is a 2D flat image


Example: Multi-view Projection


Multi-view Lines


Multi-view: Planes


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.


The views are laid flat by “unfolding the glass box”

This forms the basis of two important multi-view drawing standard:a) Alignment of viewsb) 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.


Fold lines are imaginary hinged edges of the glass boxi. 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.


View Placement


View Placement

The arrangement of views may vary as shown, where the top view is considered the central view.


Angle Projection

There are two standard arrangement of all six views of an objecti. First-angle projectionii. Third-angle projection

Each uses different symbol The names are derived from the method

used to view the object being drawn


In 1st angle projection, the object is placed in the first quadrant. In 3rd angle projection, the object is placed in

third quadrant.


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


Example: 1st and 3rd angle view projection


1, 2 and 3 view drawing


Step in creating multi-view drawing


Before start drawing, produce sketch on rough paperi. Decide on front view

and projection angleii. Obtain the overall

width, height and depthiii. Place the views (in

block)iv. Determine approximate

space between the views

v. Sketch the component, place dimensions


Creating 3-view drawing

1. 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



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 26PTT 105/3 Engineering Graphicss


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



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


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


View Selection

2. Define the front view. Should show the object in natural state and show most

features


View Selection

3. Determine the minimum number of views needed to completely describe the object.

4. Determine other views that fewest number of hidden lines


Line Convention


THANK YOU…


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