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14773 chapter 07 14773 chapter 07 Presentation Transcript

  • Mechanical Sciences-I
    Chapter 7: Orthographic Projections
  • Introduction to Orthographic Projections
    Introducing Orthographic Projections as the language of engineering designers
  • Orthographic Projections
    • Orthographic projections are an engineer’s language for conveying the shape and size information about the products he designs.
    • An orthographic projection consists of the view obtained view when the object is viewed from very far away, so that the resulting rays are all parallel.
    • The parallel rays that are used for constructing the views are called projectors.
    Vijay Gupta
  • Orthographic Projections
    • The three principal views are take on picture planes which are held parallel to the three principal faces of the object, the front, the top and the side.
    • The intersections of the projectors with the picture plane are the projections of the points from which the projectors emanate.
    • The points are joined to obtain the views.
    Vijay Gupta
  • We consider here the development of the orthographic views of a simple object.
    Object
    Vijay Gupta
  • For the Top view we view from the top!
    Viewing
    Direction
    Picture Plane
    Vijay Gupta
  • Viewing
    Direction
    Projectors
    Perpendicular to picture plane
    Point of intersection with picture plane

    Vijay Gupta
  • Viewing
    Direction




    Intersections of all
    extreme points
    Vijay Gupta
  • Top View
    Vijay Gupta
  • Similarly, viewing from the front with parallel projectors
    Front View
    Vijay Gupta
  • Top & Front Views
    on opening up the page
    Notice the interrelation
    Vijay Gupta
  • Similarly, the
    Right Side View
    Again notice the interrelation
    Vijay Gupta
  • Mitre
    The third view can also be obtained by taking projections from the two views, using the mitre line, a line at 450
    Vijay Gupta
  • Two types of projections commonly used: I & III angle
    I-Angle
    In third angle, picture planes in between the viewer & object
    In first angle, picture plane behind the object
    III-Angle
    Vijay Gupta
  • Opening up of the box with the various views in III angle
    Vijay Gupta
  • The relationship on plane paper of the various views in III angle
    III Angle
    Top
    View
    Front
    View
    Right
    View
    Left View
    Vijay Gupta
  • Vijay Gupta
  • I-Angle
    The relationship on plane paper of the various views in I angle
    Front
    View
    Left View
    Right
    View
    Top
    View
    Vijay Gupta
  • Vijay Gupta
  • Mitre
    Front
    Top View
    Front View
    Vijay Gupta
  • Top View
    Front
    Front View
    Vijay Gupta
  • Drawing three views in III angle
    Mitre
    Top View
    Front
    Front View
    Vijay Gupta
  • A Video
    Engg_graphics.mpg
  • A demonstration
    Vijay Gupta
    Gboxw31.exe
  • Front
    Vijay Gupta
  • Front
    X
    X
    X
    X
    X
    X
    X
    X
    Vijay Gupta
  • Notice that the oblique face of the cylinder appears as an ellipse in right-side view, but as lines in the front view.
    Front
    Vijay Gupta
  • Hidden Features
  • Hidden Features
    Shown by dashed lines
  • Hidden Features
  • Hidden Features
  • Hidden Features
  • Hidden Features
  • Lines and Areas
    • Projections of lines and areas
    • Meaning of lines and areas in orthographic projections
  • Projection of Lines
    A
    B
  • Projection of Lines
    • A line may be projected in its true length
    • A line may be fore-shortened
    • A line may have a point as its projection
  • Meaning of Areas in Orthographic Views
    1. A surface in true shape
    2. A foreshortened surface
    3. A smoothly curved surface
    4. A combination of tangent surfaces
  • Meaning of Areas in Orthographic Views
    B
    B
    B
    Foreshortened Surface
    Surface in True shape
  • Meaning of Areas in Orthographic Views
    C
    C
    D
    D
    C
    D
    Curved Surface
    Tangent Surfaces
  • Projections of Areas
    Some areas are projected in true shapes, while others are distorted.
    Areas parallel to picture planes are in true shapes
    Four types of Areas
    1.A surface in true shape
    2. A foreshortened surface
    3. A smoothly curved surface
    4. A combination of tangent surfaces
  • Reading Areas
    • A plane surface will always appear in a principal view as a line or an area
    • An plane surface that appears as a line in one view is normal to that view. It may or may not appear its true shape in the other views.
    • An plane surface that appears as a line in two of the principal viewsappears as a true shape in the third view.
  • Reading Areas
    • A plane surface that appears as an area in two of the principal views can not be in true shape in any view.
    • Any view that shows a plane surface as area shows it in a like shape
  • Reading Areas
    Adjacent Areas lie in different planes. If two areas were in the same plane, there will not be any boundary between the two.
    Oblique surfaces appear as areas of like shape in all views
  • Reading Areas
  • Reading Areas
  • Reading Areas
  • Meaning of Lines in Orthographic Views
    Three possible interpretations:
    An edge view of a surface
    An intersection of two surfaces
    A surface limit - reversal of direction of a curved surface
    (Surface Limit)
  • Meaning of Lines in Orthographic Views
    • An edge view of a surface
    • An intersection of two surfaces
    • A surface limit - reversal of direction of a curved surface
  • Meaning of Lines in Orthographic Views
    Another Example
  • We next illustrate how to read the orthographic drawings. This is done by interpreting the three view to ‘draw’ the represented by those view.
  • Reading Lines & Areas
    Start with a cuboid
    3
    6
    2
    7
    1
    Right front corner is cut away to represent surface 12345
    3
    1
    2
    Top front of the upper step is removed to reconcile the slope of 23 in side view.
    4
    5
    Front top is cut away to create a step 1267
  • Interpretation of Hidden Lines
  • Draw the pictorial views of the object whose three views are shown.
  • Draw the pictorial views of the object whose three views are shown.
  • Missing Line Exercises
    In the examples that follow, one or more lines may be missing in (only) one view. Try constructing a pictorial view to determine what line(s) are missing.
  • Missing Line Exercises
    One or more lines may be missing in (only) one view. Try constructing a pictorial view to determine what line(s) are missing.
  • Missing Line Exercises
  • Missing Line Exercises
  • Missing Line Exercises
  • Missing Line Exercises
  • Missing Line Exercises
  • Missing Line Exercises
  • Missing Line Exercises
  • Missing Line Exercises
  • Missing Line Exercises
  • Missing Line Exercises
  • Missing Line Exercises
  • Missing Line Exercises
  • Missing Line Exercises
  • Missing Line Exercises
  • Missing Line Exercises
  • Missing Line Exercises
  • Missing Line Exercises
    ?
  • Missing Line Exercises
  • Missing Line Exercises
  • Missing Line Exercises
  • Sectional Views
  • Sectional Views
    Whenever a representation becomes confused due to too many essential hidden details that it is difficult to interpret, sectional views are employed
  • Too many hidden lines
    Too complicated to interpret
  • Sectional Views
    • A portion of the part is cut away to reveal the interior.
    • For this purpose a cutting plane is employed. The shape of the object is clarified by distinguishing between the areas where the cutting plane actually cuts the solid material and the areas where it meets voids.
    • Wherever the cutting plane cuts the solid material, the area is hatched
  • Sectional Views
    A
    The structure of this pulley becomes clearer if we imagine the pulley is cut at the meridian plane, the material to the left of the cutting plane is removed and a projection viewing from the left is drawn.
    A
  • Sectional Views
    Cutting Plane
    The details of the hub are now clearer.
  • Sectional Views
    A sectional view makes things much clearer.
  • Sectional Views
  • Sectional Views
    This does not differentiate cut and uncut portions
    Note that the cutting plane line is long dash – two short dashes line
  • Sectional Views
    Hatch the solid portions which are exposed freshly by the cutting plane
    These areas not hatched because the cutting plane does not cut any material here. These represent holes.
  • Sectional Views
    5/4 ream
    Clarify the view using sections.
  • Sectional Practices
    In the following slides we show some sectioning practices. The principle involved in these practices is to reduce the drawing effort as much as possible while maintaining clarity as much as possible.
    • Try reducing the number of views required.
    • Draw as few hidden lines as possible. Use a variety of sections as required.
  • Offset Sections
    Note that the sectioning plane is offset to bring out both the hidden features in one view
  • Full Sections
  • Half Sections
    In many symmetrical objects one can show the internal & the external feature in the same view by considering a plane which cuts only one half the object.