Tuesday, June 7, 2011

DRAWING CLASS NOTES

Creating engineering drawings is a whole subject area of its own; there are whole degrees given in Drafting Technology.  It is also a time-honored art form.  Drawings are used all fields of Engineering (Mechanical, Civil, Architectural, Electrical, Aerospace, etc.)  The type of drawings we will be creating in this class are Mechanical, but the concepts are all transferable to the other Engineering fields. The main purpose of engineering drawings is to communicate to other engineers, machinists, etc. Drawings do the communication best merely because a picture is worth a thousand words.  Giving all of the information needed to make the product and being accurate in that information is the main goal.  Engineers are very picky about their drawings and must pay attention to detail.
Below are the basics concepts of Engineering Drawings.  The attempt here is to take volumes of drafting text material and boil it down to just what you need for this class.
They include:

  • Orthographic Views


  • Half Views and Partial Views

  • Linetypes

  • Dimensions and Notes

  • Half Views and Partial Views

  • Auxiliary Views

  • Section Views


  • Full Section

  • Half Section

  • Offset (Sketched) Section

  • Revolved Section

  • Broken Out (Local) Section

  • Detailed Views

  • Conventional Breaks

  • Scaling


    • ORTHOGRAPHIC VIEWS
    Orthographic Views are two-dimensional views of objects where the viewpoint of the object is at right angles to (or looking directly at)  surfaces.  They are used in technical and engineering drawings for accuracy.  If one's viewpoint is not at right angles, it is considered a "Foreshortened" view.
    You can also think of these views as an object inside a box with its surfaces "projecting" on to the sides of the box.  You can then unfold the box to project the views on a flat surface.

     Because the views are only two dimensional, more than one view is needed to completely describe the object.  Usually two or three views is enough (Front, Top and Side), but often more are required.
     
    Traditionally, the views contain dimensions as follows:
       
      VIEW DIMENSIONS
      Front Width and Height
      Top Width and Depth
      Side Width and Height


    LINETYPES
    OBJECT LINES
    Object lines depict the visible edges of an object.  The edges you would see looking at the object with your naked eyes.  They shown as dark, solid lines.
    HIDDEN LINES
    Hidden lines depict invisible edges inside an object.  The edges you would not see looking at the object with your naked eyes.  They are shown as dashed lines.
    CENTER LINES
    Center lines depict the center of any cylindrical-shaped object whether it be a cylinder or hole.  They are shown as a long line followed by a short line, followed by a long line.
     

    DIMENSIONS, THEIR COMPONENTS AND NOTES
    Dimensions tell how far it is from one point on an object to another point.  The most basic type is called a Linear Dimension because it gives the straight-line distance from one point to another.  There are also Radial, Diameter and Angular Dimensions. Dimensions have four basic components:
    • Dimension Text
    • Dimension Line andArrows
    • Extension Lines
    • Gap
    Note that the extension lines can cross over Object Lines (Visible Edges of the Object) to reach their destination, but still leave a gap.
    Notes are added text to describe things on the drawing.  The simplest type is just text, as in the title of the drawing.  The other type of note contains a leader, which is an arrow that points to the subject of the note.
    The box around the drawing is called the Title Block or the Format.

    BASIC DIMENSIONING TIPS:
     
    ARROW AND TEXT PLACEMENT
    The Placement of your dimension lines (arrows) and dimension text depends on the amount of space there is between the extension lines.




    HALF VIEWS AND PARTIAL VIEWS
    Half Views and Partial veiws are used to simply save space when half of, or portion of a view is not needed or is redundant.
    AUXILIARY VIEWS
    Auxiliary Views are used to accurately depict features on Inclined Surfaces.  If there is no feature on the inclined surface, there is no need to create an auxilliary view.
     


    SECTION VIEWS
    Section views are used to get rid of the confusing hidden lines:
     
     They are a way to, in our imagination, cut through an object and create an orthographic view inside the object.  It is as if the object were cut in two.
    Where the object is cut is called the cutting plane and the direction of view is depicted by arrows.  The SECTION A-A note is for use if the view is on a different page from the main views.

    The material that is supposedly cut is "Hatched" with patterns.  The patterns often depict the actual material of the object.
      

    FULL SECTIONS
    Full section views cut all the way across the object. Full Section Views can be placed on the same page or on another page.
    The Cutting Plane and Arrows always are displayed.





    HALF SECTIONS
    Half Section Views are used primarily on symmetrically shaped objects (where both halves are the same). They are a great shortcut because you can depict  the inside and outside of the object all in one view. Half Section Views can be placed on the same page or on another page.
    If the view is displayed on another page, the Cutting Plane and Arrows always are displayed.


    OFFSET (SKETCHED) SECTIONS
    Offset Section Views (Called Sketched Sections in Pro/E) are like full section views except that the Cutting Plane bends to follow certain features inside the object. Offset Section Views can be placed on the same page or on another page.
    The Cutting Plane and Arrows always are displayed.






    REVOLVED VIEWS
    Revolved Views are a shortcut way to show a section view that shows the internal shape of an object without creating a completely separate section view.    The cutting plane passes through the object at the desired location and is revolved, in place, to show the section view.  Revolved Section Views are placed on the same page. Revolved Views can be inside the regular view:

     




    BROKEN OUT (LOCAL) SECTIONS
    Broken Out Sections (Called Local Sections in Pro/E) are another sectioning shortcut.  It is a way to make a section veiw of only a specific and usually small area. Broken Out Section Views are placed on the same page.
    The Cutting Plane and Arrows are not displayed.



    DETAILED VIEWS
    Detailed views are created to show small, detailed areas of a view in a special scaled-up view.  The scale is usually twice that of the normal view.  Detailed Views can be placed on the same page or another page.



    CONVENTIONAL BREAKS
    Conventional Breaks are a way of depicting a very long object without showing the entire length.  It is often used for objects like rods, tubing/piping or wooden objects


    SCALING
    Scaling is used to depict objects on paper that are either larger or smaller than the paper.
    • If the object is larger than the paper, then the views of the object are scaled Down
    • If the object is smaller than the paper, then the views of the object are scaled Up
    • If the object fits on the paper, then the views are depicted at Full scale  (1:1)
    In Mechanical Drawings, we generally use Decimal Inch or Metric scaling The number on the left of the colon indicates the units on the Page.
    The number on the right of the colon indicates the Units on the Object or PAGE:OBJECT
     
    You want to think of it like this when you see a Decimal Inch scale of 1:2
    ONE UNIT ON THE PAGE = TWO UNITS ON THE OBJECT, or 1/2 Scale.

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