Transcript Sketching – the language of engineers
Engineering Graphics II Projection Theory and Multiview Drawings
Prof. Jon Southen October 10, 2008
Text Reference Bertoline-Wiebe,
Fundamentals of Graphics Communication
, Chapter 5
Projection Theory Scheme for representing 3-dimensional objects in a 2-dimensional medium (paper or computer screen) Can represent all 3 dimensions in a single image or use multiple views Working drawings are the practical result
Projection Theory Based on two concepts: Line of Sight An imaginary ray of light between the observer’s eye and the object Start at single point for perspective projections and are parallel in parallel projections (surprising!) Plane of Projection An imaginary flat plane (paper, computer screen) upon which the image created by the lines of sight is projected
Perspective Projection
Parallel Projection
Projection Theory Perspective projections mimic what the eye sees, but are more difficult to construct and do not show the true dimensions of the object Parallel projections are most commonly used in engineering graphics
Orthographic Projection A parallel projection where the plane of projection is perpendicular to the lines of sight Can produce either pictorial drawings that show all three dimensions at once, or multiview drawings that show only two dimensions at a time
Multiview Drawings Engineering drawings are used to manufacture or construct whatever the object is Pictorial drawings (perspective or orthographic) distort dimensions and/or angles, making fabrication difficult Multiview drawings show the true size and shape of the two dimensions shown
Pictorial Distortion
A Multiview Drawing by Albrecht Dürer (1471-1528)
Multiview Projection True size and shape Angles are correct Circles are round Lengths are to scale
Multiview Projection Set of 2-D views representing 3-D object.
Views are projections on sides of ‘box’ containing object.
Drawing formed by unfolding box
Drawing formed by unfolding box
Most Common Views Top (or Plan) Front View (or Elevation) Right Side View (or Profile) Cross sections show interior of object – later!
Projection Angle In Europe, First Angle Projection is used In North America, and in ES050, Third Angle Projection is used Be sure to select
Third Angle Projection
for your drawings
First-Angle Projection (Europe)
Third-Angle Projection (North America)
Standard Practices Choose front view as most descriptive Determine views to best represent object Use minimum number of views to completely describe object Align views correctly
Line Conventions Hidden Lines Some features may not be visible in a given view, but are still important.
E.g. holes, surfaces, change of planes Hidden features are represented with a dashed line
Hidden Lines
Line Conventions Center Lines Used to indicate the axes of symmetrical parts and features (holes, cylinders, etc.) Consist of alternating long and short thin dashes
Center Lines
Line Precedence
Visible lines have top priority Hidden lines do not cross or have priority over visible lines Centre lines do not cross or have priority over visible or hidden lines
How to Create 3-View Drawings Block in front, top and right side views using the overall width, height and depth.
Sketch the front.
Using construction lines project to top and right.
Block in major features seen in each view
How to Create 3-View Drawings
How to Create 3-View Drawings
How to Create 3-View Drawings
Draw Multiview E-drawing solution
Draw Multiview
Draw Multiview
Draw Multiview