There are two sets of standards used to define the projection and placement of orthographic views: the ANSI and the ISO. The ANSI calls for orthographic views to be created using third-angle projection and is the accepted method for use in the United States. See the American Society of Mechanical Engineers (ASME) publication ASME Y14-3-2003. Some countries other than the United States use first-angle projection. See ISO publication 128-30.
This chapter has presented orthographic views using third-angle projections as defined by ANSI. However, there is so much international commerce happening today that you should be able to work in both conventions, just as you should be able to work in both inches and millimeters.
Figure 4-54 shows a three-dimensional model and three orthographic views created using third-angle projection and three orthographic views created using first-angle projection. Note the differences and similarities. The front view in both projections is the same. The top views are the same, but are in different locations. The third-angle projection presents a right side view, whereas the first-angle projection presents a left side view.
Figure 4-55 shows the drawing symbols for first- and third-angle projections. These symbols can be added to a drawing to help the reader understand which type of projection is being used. These symbols were included in the projections presented in Figure 4-54.
Third- and First-Angle Projections
Figure 4-56 shows an object with a front orthographic view and two side orthographic views: one created using third-angle projection, and the other created using first-angle projection. For third-angle projections, the orthographic view is projected on a plane located between the viewer’s position and the object. For first-angle projections, the orthographic view is projected on a plane located beyond the object. The front and top views for third- and first-angle projections appear the same, but they are located in different positions relative to the front view.
The side orthographic views are different for third- and first-angle projections. Third-angle projection uses a right side view located to the right of the object. First-angle projections use a left side view located to the right of the object. Figures 4-57 and 4-58 show the two different side view projections for the same object. For third-angle projection, the viewer is located on the right side of the object and creates the side orthographic view on a plane located between the view position and the object. The viewer looks directly at the object. For first-angle projection, the viewer is located on the left side of the object and creates the side orthographic view on a plane located beyond the object. The viewer looks through the object.
To help understand the difference between side view orientations for third- and first-angle projections, locate your right hand with the heel facing down and the thumb facing up. Rotate your hand so that the palm is facing up—this is the third-angle projection orientation. Return to the thumb up position. Rotate your hand so that the palm is down—this is the first-angle view orientation.
To create first-angle projections using Inventor:
Start a New drawing using the ISO.idw template.
This template will automatically create first-angle projection drawings.
Click the Base tool.
Select the appropriate file.
Select the orientation.
Use the Projected View tool to select and position the views (Figure 4-59).