Slide Set 3 – Orthographic Projection II – （幻灯片设置3 -二正射投影）.pdfVIP

BNG 101 – Engineering Graphics Slide Set 3 – Orthographic Projection II – Isometric Projection (Read Planchard 2-1 to 2-10) Projections Types of axonometric projections Dimetric Two of the three axes have equal angles (usually around 105°) Types of axonometric projections Trimetric There are no equal angles between the coordinate axes Types of axonometric projections Isometric All the angles between the coordinate axes are equal (120°) Comparing axonometric views /blog/img/2009_09_22/axonometric_projections.jpg Isometric projection – a closer look What is the true angle between the axes? Do the sides shown represent the true lengths of the cube sides? Isometric projection – a closer look 1 0.82 What is the true length of the cube sides? Isometric projection versus drawing Circles in isometric drawings • Circles cannot be transferred directly to the isometric drawing. As the object is rotated to view it as isometric, holes and cylindrical features also rotate and appear as ellipses rather than true circles Isometric Limitations Exercise 1 Draw the isometric view of a cube with side lengths 25 mm (spacing between lines on your isometric paper is 5 mm). The “front” face is drawn for you below: Isometric drawing orientation How do we know which octant the cube goes in? Exercise 2 Draw the isometric view for the following object (spacing is 5 mm). Use point “O” for orientation: Exercise 3 Draw the isometric view for the following object (spacing is 5 mm). Use point “O” for orientation: (final shape) Let’s see how we got the answer using subtractive steps Exercise 3 (cont.) Exercise 3 (co