1 of 4 LESSON #13 A REVIEW OF ORTHOGRAPHIC PROJECTION What is drafting? As explained in a previous lesson: Drafting is a Graphic Language that uses Lines, Symbols and Words to describe any object that may be manufactured or constructed. Often referred to as The Language of Industry and having its own Alphabet in form of lines and using established Methods of graphically displaying two dimensional and three dimensional objects The Language of Industry is the most important tool designers and draftsmen have to convey ideas to others. What is Orthographic Projection? Orthographic Projection is the accepted method used world wide in engineering classes such as Technical Drawing and in industry to display any object as a series of projected views. Most frequently these views are the Top, Front, and Right Side. 1 of 4

2 of 4 How are edges shown in Orthographic Projection? The outside edges of an object are shown using solid lines called Object Lines or Visible Object Lines through out the views of the object. When an edge of a design detail is not able to be seen in the views then the edge is shown using an Invisible Line or Hidden Line. A hidden line is a line drawn with a series of dashes equal in length and spacing. example: A square containing a hole through its length and centered on the surface of the square will in the TOP view display object lines representing the four sides of the square and a solid circle representing the hole. In the FRONT view the outside edges will be shown as solid object lines and the edges of the circle will be projected as HIDDEN LINES since you are unable to see the edges through the thickness of the square. 2 of 4

A SIMPLE REMINDER The Autocad software provides all of the Linetypes needed to technically draw the views of objects. What does the term Detail mean? A detail is defined as a drawing having Several Views with Dimensions. The drawing can be an isometric with in isometric dimensions or one, two or three orthographic views with dimensions throughout the views. A detail in Cad Class describes any of the problems contained within the class workbooks and hand out sheets. As you look through the CAD WORKBOOK in class you will see many DETAILS (assignments /problems) shown using several technical methods of display. Some drawings contain only one view, others are displayed with several views and many are displayed as isometrics (picture like form). 3 of 4

After you complete this lesson please study the different displayed details in the Class Workbook. A good understanding of them will help to improve your ability to READ technical drawings. Take a close look at the very first detail shown in isometric on page 19 of the ASSEMBLY AND DETAILS portion of the CAD Workbook. The L Block detail will be used as a demo problem in The Orthographic Projection_ Presentation NOW OPEN The Orthographic Projection_Presentation 4 of 4