1. Let’s make engineering more easy
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Let’s make engineering more easy
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2. Orthographic Projection Part-1
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3. PROJECTION METHOD
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4. Line of sight is an imaginary ray of light between an
observer’s eye and an object.
There are 2 types of LOS :
parallel
and
converge
Parallel projection
Perspective projection
Line of sight
Line of sight
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5. Plane of projection is an imaginary flat plane which
the image is created.
The image is produced by connecting the points where
the LOS pierce the projection plane.
Parallel projection
Perspective projection
Plane of projection
Plane of projection
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6. Disadvantage of Perspective Projection
Perspective projection is not
used by engineer for manu-
facturing of parts, because
1) It is difficult to create.
2) It does not reveal exact
shape and size.
Width is distorted
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7. Orthographic Projection
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8. MEANING Orthographic projection is a parallel projection technique
in which the parallel lines of sight are perpendicular to the
projection plane
Object views from top 1 2 1 5 2 3 4 5 3 4
Projection plane
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9. ORTHOGRAPHIC VIEW NOTES
Orthographic projection technique can produce either 1. Multiview drawing that each view show an object in two dimensions.
2. Axonometric drawing that show all three dimensions of an object in one view.
Both drawing types are used in technical drawing for communication.
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10. Axonometric (Isometric) Drawing
Advantage
Easy to understand
Disadvantage
Shape and angle distortion
Example
Distortions of shape and size in isometric drawing
Circular hole becomes ellipse.
Right angle becomes obtuse angle.
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11. Multiview Drawing Advantage Disadvantage Example
It represents accurate shape and size.
Disadvantage
Require practice in writing and reading.
Example
Multiviews drawing (2-view drawing)
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12. IT IS A TECHNICAL DRAWING IN WHICH DIFFERENT VIEWS OF AN OBJECT
ORTHOGRAPHIC PROJECTIONS:
IT IS A TECHNICAL DRAWING IN WHICH DIFFERENT VIEWS OF AN OBJECT
ARE PROJECTED ON DIFFERENT REFERENCE PLANES OBSERVING PERPENDICULAR TO RESPECTIVE REFERENCE PLANE
Different Reference planes are
Horizontal Plane (HP),
Vertical Frontal Plane ( VP )
Side Or Profile Plane ( PP)
And
Different Views are Front View (FV), Top View (TV) and Side View (SV)
FV is a view projected on VP. TV is a view projected on HP. SV is a view projected on PP.
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14. Defining the Six Principal Views or Orthographic Views
Orthographic Projections are a collection of 2-D drawings that work together to give an accurate overall representation of an object.
Defining the Six Principal Views or Orthographic Views
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15. Auxiliary Vertical Plane (A.V.P.) Auxiliary Inclined Plane (A.I.P.)
PLANES
PRINCIPAL PLANES
HP AND VP
AUXILIARY PLANES
Auxiliary Vertical Plane
(A.V.P.)
Auxiliary Inclined Plane
(A.I.P.)
Profile Plane
( P.P.) 
A.V.P.
A.I.P.
 to Hp &  to Vp
 to Vp
 to Hp
& 
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16. PICTURE
PLANE
Object
Observer
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20. Glass Box Approach
The object, whose orthographic projection needs to be drawn, is enclosed in a glass-box
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21. Glass Box Approach Project points on the front view of the glass-box
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22. Glass Box Approach
Project points on the the top view of the glass-box, just as done for front
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23. Glass Box Approach
Project points on the right view of the glass-box, just as done for front and top
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24. Glass Box Approach Unfold the glass box, see how the views align
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25. Glass Box Approach Unfold the glass box, see how the views align
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26. First and Third Angle Projections
First-angle Projection
Instructor:
Third angle projection is normally used in the US while Europe uses the First Angle projection. Note the symbols at the bottom of each one which tell you which projection that you are viewing.
These can be confusing to students. We are only highlighting the fact that there are different ways to represent projections. It is not expected for students to fully understand the differences.
From Fundamentals of Graphic Communications by Bertoline, McGraw-Hill
First Angle
Third Angle
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27. Conventional Orthographic Views
Height
Depth
Width
Front View
Top View/Plan
Right Side View
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28. Line Thickness Line Styles
Lines on an engineering drawing signify more than just the geometry of the object and it is
important that the appropriate line type is used.
Line Thickness
For most engineering drawings you will require two thickness', a thick and thin line.
The general recommendation are that thick lines are twice as thick as thin lines.
                                             
A thick continuous line is used for visible edges and outlines.
A thin line is used for hatching, leader lines, short centre lines, dimensions and projections.
Line Styles
Other line styles used to clarify important features on drawings are:
                                            
Thin chain lines are a common feature on engineering drawings used to
indicate centre lines. Centre lines are used to identify the centre of a circle,
cylindrical features, or a line of symmetry.
                                             
Dashed lines are used to show important hidden detail for example wall
thickness and holes..
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29. Precedence of Lines
Visible lines takes precedence over all other lines
Hidden lines and cutting plane lines take precedence over center lines
Center lines have lowest precedence
0.6 mm
From: Bertoline, Figure 2.40/ Pg 43
Note the thickness specified for given three types of lines
The precedence of lines governs which lines are drawn when more than one line occupies the same position on a drawing.
For example the figure above shows that while a visible line takes precedence over all other lines, hidden line and cutting plane line take precedence over center lines.
Standard engineering drawing practices requires the use of standard linetypes, which are called the alphabet of lines. The sizes show the recommended line thicknesses.
0.3 mm
0.6 mm
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30. For Example: 1. Visible 2. Hidden 3. Center
From Bertoline: Figure 2.38 / Pg 42
In engineering and technical drawing, it is important that hidden features be represented, so that the reader of the drawing can clearly understand the object.
Thus we need hidden lines to emphasize that those features exist and are hidden in that particular view.
We also need center lines to understand how the features defined in the 2D views translate into 3D.
NOTE: It must be emphasized that hidden lines and center lines are used only on Orthographic projection drawings, never on isometric drawings
Q: Do we need a convention for what line to show if two lines fall on top of each other?
A: Yes! Otherwise features which are more important (eg: visible lines) would be overridden by less important features (eg: hidden lines) and the resulting drawing would be interpreted inaccurately. The next slide shows the convention followed.
2. Hidden
3. Center
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31. Dimensioning
A dimensioned drawing should provide all the information necessary for a finished product or part to be manufactured. An example dimension is shown below.
                                                                                                                                                                                                       
Dimensions are always drawn using continuous thin lines. Two projection lines indicate where the dimension starts and finishes. Projection lines do not touch the object and are drawn perpendicular to the element you are dimensioning.
All dimensions less than 1 should have a leading zero. i.e. .35 should be written as 0.35
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32. Types of Dimensioning Parallel Dimensioning
Parallel dimensioning consists of several dimensions originating from one projection line.
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33. Superimposed Running Dimensions
Superimposed running dimensioning simplifies parallel dimensions in order to reduce the space used on a drawing. The common origin for the dimension lines is indicated by a small circle at the intersection of the first dimension and the projection line.
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34. Chain Dimensioning Combined Dimensions
A combined dimension uses both chain and parallel dimensioning.
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35. Dimensioning of circles
(a) shows two common methods of dimensioning a circle. One method dimensions the circle between two lines projected from two diametrically opposite points. The second method dimensions the circle internally.
(b) is used when the circle is too small for the dimension to be easily read if it was placed inside the circle.
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36. Dimensioning Radii
All radial dimensions are proceeded by the capital R.
shows a radius dimensioned with the centre of the radius located on the drawing.
(b) shows how to dimension radii which do not need their centres locating.
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37. Tolerancing
It is not possible in practice to manufacture products to the exact figures displayed on an engineering drawing. The accuracy depends largely on the manufacturing process. A tolerance value shows the manufacturing department the maximum permissible variation from the dimension.
Each dimension on a drawing must include a tolerance value. This can appear either as:
a general tolerance value applicable to several dimensions. i.e. a note specifying that the General Tolerance +/- 0.5 mm.
or a tolerance specific to that dimension
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38. values read from bottom and Right side Unidirectional System
Aligned System
values read from bottom and Right side
Unidirectional System
values read from bottom only
(Preferred when?)
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39. INCORRECT
CORRECT
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40. Dimensioning a circular arc.
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42. Omit unnecessary dimensions.
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43. Use of enlarged view to clarify dimensions.
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