Multiview Drawings In engineering, various methods are used to represent objects. Among these, the engineering drawing or multiview drawing is a major means of communicating the design concept. In this method, orthogonal projection is used to draw and define an object. Orthographic Projection Pictorial drawings provide a three dimensional view of an object as it would appear to the observer. Generally, multiview and pictorial drawings are used together to provide a complete picture of the object being represented. Pictorial Drawing Projecting Views Orthographic projection is the system of representing objects by using more than one view to define the object. There are actually 4 methods of orthographic representation. In this course you will be studying and using the Third-Angle Projection method of representation. Third-Angle Projection is the most widely used method today. The Third-Angle projection method is an orthographic representation in which the object to be represented and seen by the viewer appears behind the coordinate viewing planes on which the object is orthographically projected. An easier way to think of this method of projection is to imagine viewing the object and its various views through a glass box. In fact, third-angle projection is sometimes referred to as the glass-box method. Each face of the box represents one of the six different planes of projection Third Angle (glass-box) Viewing Planes Using this method, each view is projected onto its respective viewing plane. Each viewing plane is referred to as a plane of projection. The six principal planes of projection are: front, top, bottom, left side, right side, and back. In determining how the particular view will look (on the plane of projection), imagine yourself looking at the object through each side of the glass box. Object with Viewing Directions Indicated View in Direction A B C D E F View From Front Top Left Right Bottom Back Generally not all of these projections are used in drawings. In determining the number of projections to use, the rule of thumb is include only as many views that are needed to represent the object accurately. When laying out your various views on your drawing, start with the Principal View. The principal view is the view that shows the most about the product. It is usually the longest view and shows the major shape or profile. Sometimes it may be difficult to determine which view should be used as the principal view. In situations such as this, use your own discretion. This principal view is then designated as the Front View. After your front view is selected, imagine folding out each flap of the box towards the front view. All 6 Orthographic Views Positioned Correctly on Drawing Surface Hidden Surfaces & Edges Many objects drawn in engineering contain many features (lines, holes, etc.) that cannot be seen when the object is viewed from a particular angle. These hidden details are normally required on the drawing to show the true shape of the object. Hidden lines are used to illustrate hidden detail. Hidden lines consist of short, evenly spaced dashes. In CAD, hidden lines are given a different color and are generally assigned to a separate layer. Sample Projections Examples of orthographic projection Examples of objects having hidden features Examples of objects having sloping surfaces Examples of objects having circular features View Spacing &Alignment For clarity and good appearance, the views should be well balanced on the drawing surface. In determining the alignment and spacing between views, the drafter must consider the size of the object to be drawn, the number of views, the scale of the printed drawing, and the space between views. When determining the space between drawings, the drafter also needs to allow for the placement of dimensions (to be covered in a later unit). When laying out your views, view alignment is a must. Actually, view alignment is a natural by-product of proper drafting technique (to be demonstrated in the first guided activity in this unit). Notice that each view is perfectly aligned with the principal view (Front View). Spacing, though important, need not be precise but should look balanced. Indicated below is one technique you may find helpful in spacing your views. First, determine the distance between borders. Next, determine the total vertical and horizontal distances of the aligned views Subtract the horizontal total from the horizontal distance between borders and subtract the vertical total from the vertical distance between borders. Then divide these totals by the number of spaces required. e.g. Consider the following drawing. Horizontal distance between borders = 10 inches Vertical distance between borders = 7.5 inches Total of horizontal distances of views = 3.5 + 2.0 = 5.5 inches Total of vertical distances of views = 1.5 + 2.0 = 3.5 inches Horizontal empty space = 10 - 5.5 = 4.5 inches Vertical empty space = 7.5 - 3.5 = 4.0 inches Horizontal distance between views = 4.5 / 3 (# of spaces) = 1.5 inches Vertical distance between views = 4.0 / 3 (# of spaces) = 1.33 inches Title Block Placement When creating engineering drawings, the drafter needs to consider title block placement as well. Title blocks are acceptable in any corner of the drawing. When considering their placement, take into account corners of the drawing that are not heavily utilized (to avoid over crowding).