2.5 Drawings Made to a Scale
If an object is drawn full size, it is said to be drawn full scale. Large objects like airplanes, automobiles, houses, ships, or skyscrapers cannot be easily drawn full size (although this is occasionally done). To get some objects to fit on the size paper being used, however, the object must be drawn to scale. When an object is drawn to scale, the object is drawn at a reduced (or in some cases, enlarged) size. The object may be drawn one-half its actual size, or half-scale. This means that every actual 1″ (25mm) on the object is drawn only 1/2″ (12.5mm). Half-scale is shown as follows: 1/2 = 1. Objects may be drawn to any scale. Some very small parts, such as those used in a watch or an electronic device, may have to be increased in size on a drawing to be seen and dimensioned more easily. The scale for such a drawing might be 10 = 1. A 1/8″ (3mm) part at a 10 = 1 scale would be drawn 1 1/4″ (30mm) in size. A 1″ (25mm) part drawn at a 4 = 1 scale would be shown as 4″ (100mm) in size.
The scale of a drawing may be shown somewhere near the actual part drawing or may be indicated in the drawing's title block. It is important to determine what scale is being used. All lines and geometric figures in a drawing are drawn to the same scale. If every line and geometric figure is not drawn to scale, it will look abnormal on the drawing. The area of a geometric figure is affected by the square of the scale factor. For example, an object in a half-scale drawing where 1/2 = 1 will actually appear 1/4 of the full size. Conversely, when the scale factor is increased, parts in a drawing with a scale of 4 = 1 will appear 16 times larger (42 or 4 squared or 4 × 4) than the actual size.
The scale of a drawing may be shown somewhere near the actual part drawing or may be indicated in the drawing's title block. It is important to determine what scale is being used. All lines and geometric figures in a drawing are drawn to the same scale. If every line and geometric figure is not drawn to scale, it will look abnormal on the drawing. The area of a geometric figure is affected by the square of the scale factor. For example, an object in a half-scale drawing where 1/2 = 1 will actually appear 1/4 of the full size. Conversely, when the scale factor is increased, parts in a drawing with a scale of 4 = 1 will appear 16 times larger (42 or 4 squared or 4 × 4) than the actual size.