At this point we have been focusing our instruction on orthographic projection. In an orthographic projection at least two views are always required to completely define an object. In orthographic projection, each view only shows two dimensions. For example, the front view of an object only shows height and width, the top view shows width and depth and the side view shows height and depth.

Learning to read orthographic projection takes practice and instruction. To aid in the instruction we have been using isometric projections of objects. Isometric projections provide visual descriptions of the object in one view. It can typically be interpreted by individuals without any specific training or instruction in the reading of engineering drawings.

Isometric projection is a type of orthographic projection. Consider the glass box. In normal multi-view orthographic projection, the object is placed inside this imaginary glass box, so that the principal faces in the object are parallel to the faces of the glass box. In isometric projection the object, instead of having its faces parallel to the plane, it is rotated and tilted in such a way that all the principal faces on the object are inclined. The projected views are then drawn connected so that they do form an object rather than separated as they are for multi-view orthographic projection. Isometric sketching is particularly useful for displaying conceptual design features on paper and communicating those features to others. Isometric sketching is a skill that takes time and practice to develop.

Initialy the use of isometric paper will be of great assistance in making isometric sketches. Isometric paper has lines dividing the paper into small equilateral triangles. Since an isometric projection of an object will show that object in a three dimensional view, the isometric graph paper must have three axis. One of this axis is usually taken as a vertical line. The other two directions make angles of 120 degrees with the vertical. In plotting size dimensions, the height of the object is measured along the vertical axis, with width and depth measured about the axis at 120 degrees to the vertical. The size of the equilateral triangles created by the intersections of these three axis, represents dimensional units to be defined by the creator of the drawing. In order for the isometric drawing to be proportionaly accurate to the object being represented, the units in each direction must be consistent. In other words, if each unit on the vertical direction is defined to be 1/2 of an inch then each unit in the depth and width direction must also be defined as 1/2 of an inch.

To begin an isometric drawing it is usually helpful to start with a rectangular cube which, defines the overall height, width and depth of the object. This rectangular cube would be sketched very lightly as many of the lines creating this rectangular cube may not be a part of the completed drawing. In the isometric view, three planes on this rectangular box will be visible. If those three planes are taken to be the three principal views given an orthographic projection, the transition from the orthographic projection to the isometric, becomes quit simple.

(Go back)