WoodDigest.com |

Last month's discussion centered on a group of industrial-based detail drawings. These drawings are used to communicate necessary information to the reader or to the draftsperson when bidding or building a project. This month, the focus will be on a group of drawings called the pictorial drawings.

Where are they used?
Pictorial drawings are used to depict a three-dimensional view of an object as if you were holding it in your hand. To convey as much information as possible, the part is best oriented to show the sides with the most features. In many cases, multi-view drawings provide information in a format that makes it difficult to visualize the completed part. Conversely, a pictorial drawing will help the reader visualize the part and aid in its manufacture. Multi-view drawings are dimensioned and are usually drawn to a scale. Although pictorial drawings may be dimensioned and drawn to scale, their main purpose is to give a three-dimensional representation of the part. Therefore, they are usually not dimensioned and exact scaling is not required. Proportions are expected to be maintained in any case.

Isometric Drawings
An isometric drawing is one form of a pictorial drawing. Most commonly used in its true form, the isometric drawing will give "equal measure" (isometric) and foreshortened views of three sides of the part. Note on Graphic 1 the three interior angles are all 120 degrees and the bottom corners of the cube are angled 30 degrees from the base line. The heights (Z-axis) are always constructed vertical and square to the horizontal line. Hidden lines are not inserted.

An isometric drawing can be easily constructed by using a 30-60-90 triangle and T-bar if drawing by hand or with CAD programming.
The isometric lines are those that are constructed either vertically or at the 30 degree angle as shown above. Nonisometric lines are those that are inclined or ramped as compared to the isometric lines. The front view from the multi-view drawing is placed in the defined area in Graphic 1. Similarly, the view from the top and right side will be shown as defined. The bottom or other views will not be shown unless the orientation of the cube is changed.

Circles or holes will be skewed or drawn within an isometric square. For example, a circle will appear elliptical in shape and is actually drawn by connecting a series of four arcs, drawn from the centerlines of the isometric square. Note Graphic 2.

The ellipses may also be drawn with the use of templates, purchased from a drafting supply store. Curved or round corners are drawn in the same manner by locating the end of the radius on the straight line, and then connect the two points to form a triangle. The third point of the arc is actually the center of the triangle. Connect the three points with a freehand arc.