Often it will be more convenient, or even necessary, to prepare isometric or oblique

Figure 5-69.-Sketching a rectangular block: A. Isometric; B. Oblique.

PICTORIAL SKETCHES instead of multi-view orthographic sketches. Pictorial sketches provide you with a quick method of examining tentative construction details. A quick pictorial sketch will also help you in the layout of isometric and oblique drawings.

The principles of pictorial and orthographic sketching are similar, except that in pictorial sketching you will be dealing with volumes rather than flat planes. Basically, pictorial sketches and pictorial drawings are practically the same except for the drawing materials used in their development and the fact that pictorial sketches are not normally drawn to scale. By following a few simple steps, based on pictorial drawing construction principles, you should be able to prepare meaningful pictorial sketches.

ISOMETRIC SKETCHES. Select a position (view) that will show the object to the best advantage. You will know what you want included in your sketch, so move either the object or yourself until you can actually see everything you want to show. If the object is something you have in mind or if you intend to sketch an isometric view from an orthographic drawing, you will have to visualize the object and assume a viewing position. In making your isometric sketch, remember that you start by sketching three isometric axes 120 degrees apart, using two angles of 30 degrees and a vertical axis of 90 degrees. Figure 5-69, view A, shows a step-by- step procedure that can be used in making an isometric sketch of a wooden rectangular block measuring 1 1/2 in. by 2 in. by 4 in.

The first step is to sketch the three isometric axes, as mentioned earlier. The second step is to mark off the 1 1/2 in. for height on the vertical axis, the 2-in. width along the left axis, and the 4-in. length along the right axis. The third step is to draw two vertical lines 1 1/2 in. high (starting with the marks on the right and left axis), then sketch parallel lines from each of the marks on the sketch. Note that the lines that are parallel on the object are parallel on the sketch. The fourth step is to dimension the sketch. The dimensions on an isometric sketch are placed parallel to the ends or edges. The final step is to check the sketch for completeness and accuracy.