1. Isometric and Orthographic Projections
D Byrne
Science and Technology Cycle II
Year 1
April 2008

2. Objectives
Understanding Graphic representations as a communication tool.
Projections
Orthographic.
Isometric.
Lines and elements.

3. What can you learn about this object from this drawing?
Could you build an accurate model only using this drawing?
What is it’s size?
What is it made of?
What does the other side of it look like?
Are there any moving parts?
What is missing that you might need?

4. Three Basic Types of Technical Drawings
Freehand sketches
Instrument drawings
Computer drawings and models

5. Introduction to Projections
Two Basic Categories
Presenting objects with 2-D media in 2-D or 3-D
Orthographic and Isometric
Pictorial
Definitions:
Projection: the process or technique of reproducing a spatial (3-D) object upon a plane or curved (2-D) surface
Orthographic sketches present the object in a series of projections, each one showing only two of the object’s three dimensions.
Pictorial sketches present the object in a single view with all three dimensions represented
Discuss the trade-offs in using any type of projection; some are more realistic, some are easier to draw, and some are easier to interpret by non-technical people

6. Projections: Four Basic Types
Orthographic
Isometric
Pictorials are 3-D
Oblique
Perspective

7. Orthographic Projections
The purpose of orthographic projections is to accurately represent object.
Accurately, means to make a drawing from which it is possible to manufacture or reproduce the object only using the drawing as a guide.

8. Orthographic Projection
By definition for each element of a orthographic projection drawing you only present 2 of the three dimensions. Think of it as an observer look at one face, what do they see.
Any orthographic projection drawing normally has three views… Front view, Top view and side view (Right or left side view)

9. The Six Principal Views or Orthographic Views
Generally do not need all six to fully describe the object. A conventional Engineering Drawing will normally have 2 to 3 views unless it required more views to describe the geometry/ profile.
We know which ones they are on the drawing, because we always present them in the same relationship to each other. I.e. Top above front, right to right of front, etc. This convention is called as the Third angle method.. The other method in which the views can be placed is the First angle method in which the Top view is below front view, Right side view is on left side of front view. For this class we will be following the Third angle convention.
These are often called orthographic projections – because the line of sight is perpendicular to the principal view

10. Defining the Principal Views or Orthographic Views
Sectional view

11. Which Views to Present? General Guidelines
The Front View that is which is the most descriptive of object.
Has normally the longest dimension as the width (or length).
Most common combination of views is to use: Front, Top, and Side View, Which ever gives all information you need to understand the object.
Views other than the Principal Views are called Auxiliary Views.

12. Normally we use the front top or right side view only
Normally we use the front top or right side view only. The 4 other views only repeat what we already can see in the these views. These views can be seen by either physically or mentally rotating the object into the appropriate position to show the detail of the object visible form that view.
Rotate 90 degrees “up” to get top view.
Rotate Back.
Rotate 90 degrees clockwise to get right side.
This give three principal views commonly used.

13. Conventional Orthographic Views
Each view is constructed so that information (dimensions, and object edges, etc ..), are clearly related to the other views.
Width
Top View
Depth
Right Side View
Top View
Front View
Height
Right Side View
Front View

14. Construction Lines
Construction lines When a drawing is rendered, basic faint lines are drawn to provide a framework for the completion of the projection.
Although not part of the object, these lines provide the framework to construct the drawing of the object.

15. Dimension Lines Top View Front View Width Depth Right Side View Height
Dimension Lines display precise information about the size of the object.
Width
Depth
Top View
Height
Right Side View
Front View

16. Object Lines Top View Front View Top View Width Right Side View
Object Lines Represent features that are only visible in the current view.
Width
Top View
Depth
Right Side View
Top View
Front View
Height
Right Side View
Front View

17. Hidden lines Top View Front View Right Side View
Hidden Lines represent features that cannot be seen in the current view. We show these unseen details, with dashed lines.
ALL Hidden or internal details must be included. What does the inside of this block look like?
Top View
Right Side View
Front View

18. Center Lines Top View Front View Right Side View
Center lines represent symmetry and mark the center of circles, the axes of cylinders, and the axes of symmetrical parts, such as bolts.
Top View
Again, though not part of the object, these lines are important elements of the objects dimension and construction.
Right Side View
Front View

19. Sectioning of a view A A Sectional view A:A
The section line labeled A:A shows the arrows pointing in the direction to which you are observing the “cut” or section. A
Section Lines Are used to represent where the object is to be “cut” or sectioned to reveal interior details. This is used when other views may not adequately reveal information about the object.
Sectional view A:A

20. Types of Lines in Orthographic Projections
Construction lines - Basic faint lines which are drawn to provide a framework for the completion of the projection.
Dimension Lines display precise information about the size of the object.
10cm
Object Lines – represent visible features for an object. They are the darkest and most present.
Hidden Lines – represent features that cannot be seen in the current view. They are as dark as the object lines.
Center lines – represent symmetry and mark the center of circles, the axes of cylinders, and the axes of symmetrical parts, such as bolts
Section Lines Are used to represent where the object is to be “cut” or sectioned to reveal interior details. This is used when other views may not adequately reveal information about the object. A

21. Review: Major views used in orthographic projections.
Isometric View
1. Object
2. Hidden
3. Center
4. Sectional

22. Isometric Drafting

23. Height
Depth
Width

24. Scale of 1:2