Thursday, April 23, 2015

Orthographic Projection

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What is Engineering Graphics?
 A set of rules and guidelines that help you create an Engineering Drawing.
  What is an Engineering Drawing? 
A drawing that communicates an idea or design.
  Mechanical Engineers (factory/manufactured parts)
Detailed drawing of a part that needs to be machined.
Electrical Engineers (appliances to power transmission)
A circuit schematic.
Circuit board layout. (electronics)
Civil Engineers (topography/landscapes)
Plans for a bridge.
Road layout. bb
Orthographic Projection
→An orthographic projection is a 2-D representation of a 3-D object.
→A system of drawings that represent different sides of an object.
→Project edges perpendicular to planes of projection
→Represent a shape using 2 or more views
→Gives enough information to manufacture the part

3D  is the ISOMETRIC VIEW                                                 2D is the ORTHOGRAPHIC VIEW
SIX PRINCIPLE VIEWS
 
The 6 principal views are created by looking at the object, straight on, in the directions indicated.


How do we create the 6 principal views?
 
The Glass Box Method
Consider a pair of dice – each number is a view.  
Choose one number for the front and then determine the remaining five views.

  The object is placed in a glass box.
The sides of the box represent the 6 principal planes.
Left, Front, Right, Rear, Top, Bottom

The image of the object is projected on the sides of the box.


VISUALIZE !!!

 
Things to notice!
The projection planes (SIDES OF BOX)
The projectors (DASHED LINES)
How surfaces A and B are projected. (Parallel FULL/non-parallel SHORTENED)
 

The box is unfolded creating the 6 principal views.

Notice the hidden lines which show features that are not directly visible from that particular view.
  

EXERCISE . . .
Label the 5 remaining principal views with the appropriate view name.  Right, Left, Rear, Top and Bottom. 


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Standard Views

When constructing an orthographic projection, we need to include enough views to completely describe the true shape of the part.
Complex part = more views are required
Simple part = less views are required

The standard views used in an orthographic projection are;
Front view
Top view
Right side view
The remaining 3 views usually don’t add any new information (but sometimes they do). 
  How many views do we need to completely describe a block?

Front view shows THE MOST features.
All other views are based upon the orientation chosen for the front view.
 Front view usually contains the least number of hidden lines.
How many views do we need to completely describe a block? 



Front View
  The front view shows the most features or characteristics of the object.
It usually contains the least amount of hidden lines.
The front view is chosen first and the other views are based on the orientation of the front view which also determines the VIEW ALIGNMENT.
View Alignment
 
The top and front views are aligned vertically (UP AND DOWN) and share the same width dimension.

The front and right side views are  aligned horizontally (SIDE TO SIDE) and share the same height dimension.
Width (vertical alignment) and height (horizontal alignment)
 





Line Type and Weight




Line type and line weight provide valuable information to the print reader.
For example, line type and weight can answer the following questions.
Is the feature visible or hidden from view?
Is the line part of the object or part of a dimension?
Is the line indicating symmetry (same on both sides of the line)?





There are four commonly used line types; (there are more than four types of lines – but these are those which are most COMMONLY used in engineering drawings).
continuous
hidden
center
phantom




Some lines are more important than others.  Importance is indicated by line weight or thickness.
The thicker the line, the more important it is.



Visible lines:
Visible lines represent visible edges and boundaries.
Continuous (no breaks/dashes) and thick (0.5 - 0.6 mm).
Hidden lines:
Hidden lines represent edges and boundaries that cannot be seen.
Dashed and medium thick                    (0.35 - 0.45 mm).


Center lines:
Represent axes of symmetry.
Long dash – short dash and thin           (0.3 mm).


Phantom line:
Phantom lines are used to indicate imaginary features. 
alternate positions of moving parts
adjacent positions of related parts 
The line type is long dash – short dash – short dash and the line weight is usually thin (0.3 mm).


Dimension and Extension lines:
Dimension and extension lines are used to show the size of an object. 
In general, a dimension line is placed between two extension lines and is terminated by arrowheads, which indicates the direction and extent of the dimension. 
The line type is continuous and the line weight is thin (0.3 mm).
  


Cutting Plane line:
Cutting plane lines are used to show where an imaginary cut has been made through the object in order to view interior features. 
The line type is phantom and the line weight is very thick (0.6 to 0.8 mm). 
Arrows are placed at both ends of the cutting plane line to indicate the direction of sight.

Section line:
Section lines are used to show areas that have been cut by the cutting plane. 
Section lines are grouped in parallel line patterns and usually drawn at a 45° angle. 
The line type is usually continuous and the line weight is thin (0.3 mm).