Line weight and line quality are extremely important to a successful set of design drawings. Usually a set of design drawings will go to many different people including the client, other designers or architects, manufacturers, builders, and others within the profession. The lines used for design drawings must be crisp and dark so that they are easy to reproduce and clear copies can be made from them.
The line weight is the light or darkness and width of a line. Manual pencil drafting, drafting in ink, and computer-aided drafting documents must have a variety of line weights. Varied drawing line weights, typically three, should be used on every drawing. These include light, medium, and bold lines. Aside from these lines used to illustrate a drawing, there are also guidelines and border lines. Guidelines are used for page layout and borderlines are used for framing the page. These different weights technically help to create an easy to understand document and artistically add visual interest to the document. These documents must also have consistent line quality, which is the uniformity of lines throughout a drawing. These two elements give a sense of professionalism to the documents, provide visual interest, create a clear and easy to read document, and demonstrate the drafting skills and abilities of the designer.
Pencil lines should be solid, uniform in width, and consistent in darkness throughout their length. If a line in a drawing needs to be changed, make sure to erase it cleanly and recreate the line in the appropriate line weight and quality. If only a part of the line needs to be modified, erase using the erasing shield and make sure the new segment and the existing segment match perfectly in width and darkness. Being consistent also applies to pen and ink drawings and CAD drawings. A pen and ink drawing is usually created first with very light guidelines. When using ink technical or drafting pens, typically the light, medium, and dark weights are created in proportion to one another. For example, if light is a width of .05, then medium is .1 and dark is .2. The actual width of each line type should also be related to the size and scale of the drawing. A drawing in 1/4" scale, like a floor plan, may need smaller pen widths than