Post on 28-Oct-2014
Objectives
• Orthographic Projections
• View Selection
• Glass Box Approach
• First and Third Angle Projections
• Line Precedence
• Two View Drawings
• Tips
Orthographic Projections
• Reference: Technical Graphics, Chap 3:
• Advantage – Represent features of an object more accurately
• Example Problem
Orthographic Projections
• 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
Which Views to Present?General Guidelines
• Pick a Front View that is most descriptive of object
• Normally the longest dimension is chosen as the width (or depth)
• Most common combination of views is to use:
– Front, Top, and Side View
• Any other view different from the Principal Views is called an Auxiliary View (see 3.15 in the Technical Graphics text)
Glass Box Approach
• Most powerful technique to understand orthographic projections
• Suspend the object with transparent strings inside a glass box
• Freeze the view from each direction (each of the six sides of the box) and unfold the box
• Animation illustrates glass-box approach
Glass Box Approach
Glass Box Approach
Glass Box Approach
Glass Box Approach
Glass Box Approach
Glass Box Approach
Third-angle Projection
First-angle Projection
First and Third Angle Projections
• First Angle – International
• Third Angle – U.S.
Conventional Orthographic Views
Height
Depth
Width
Front View
Top View
Right Side View
Is The Orthographic View OK?
Orthographic Must Be In Projection
Hidden and Center Lines• Hidden Line – used to represent features that
cannot be seen in the current view
• Centerlines – used to represent symmetry and to mark the center of circles and the axes of cylinders, and the axes of symmetrical parts, such as cylinders and bolts
For Example:
1. Visible
2. Hidden3. Center
• Visible lines takes precedence over all other lines
• Hidden lines and cutting plane lines take precedence over center lines
• Center lines have lowest precedence
Precedence of Lines
0.70 mm
0.35 mm
0.35 mm
Example: Application of Precedence
Intersecting Lines in Orthographic Projections
Solid Line Intersections
Dashed Line Special Case Intersections
Gap
Two-View Drawings• Some objects can be fully described by
two views, look for:
– Symmetry or Bodies of Rotation
Front View Right Side View
Front View
Right Side
Other Two-View Examples
Review Questions• Rectilinear grids are used for sketching
isometric pictorials … True/False
• Based on the lines of sight, orthographic projection drawings are classified as ___________ projections
• There are ____ standard principal views of orthographic projections
• Each view in an orthographic projection concentrates on ____ dimensions of the object
Hints for Orthographic Projection Sketching
• Identify the major features and overall dimensions of the object
• Do not use any straight-edge devices as a pencil guide when sketching by hand
• Start by drawing bounding boxes with light construction lines.
• Keep views aligned while sketching
Hints for Orthographic Projection Sketching• Title Information is required – follow
conventions
• Usage of construction lines is encouraged.
– Mandatory for circle or ellipse
• Orthographic projection:
– Alignment of the views is important!
– Will not be graded, if not aligned
Hints for Orthographic Projection Sketching
• Map inclined and oblique faces to all three views
• Follow the precedence of lines
• Darken all visible, hidden, and center lines
Sketching a Circle• Draw a square whose
sides are the diameter of the circle.
• At the center of each side define the point of tangency for the circle.
• Draw the diagonals of the square.
• Orient the paper so you can draw equal arcs to construct the circle