Lines are the universal language of a machining drawing, and they have plenty to say. It's a designer's way of communicating the information the craftsman needs to create, assemble, service, or inspect a product, part, or component. Lines have a specific weight (thickness) and form that combine with other features to provide the information a skilled worker needs to understand the drawing.
Next are descriptions of the most common lines you'll find on a blueprint, followed by a look at the lines themselves:
- Visible line: A thick continuous line outlining the edges or contours of an object.
- Hidden line: The hidden line shows edges, surfaces, and corners that cannot be seen. It is a medium-weight line consisting of short dashes about 1/8" long with 1/16" gaps.
- Centerline: Used to indicate the centers of holes, arcs, and symmetrical objects, the center line is a very thin long-short-long line.
- Dimension and extension lines: The dimension line is thin and solid, indicating the size of an object. Arrowheads at each end show where the dimension lines end at the extension lines.
- Short and long break lines: Break lines remove a section of a drawing for clarity, and shorten objects that are too long to fit on the drawing.
- Phantom line: Phantom lines are thin long-short-short-long lines that show the movement of an object, a part in an alternate position, or adjacent objects or features.
- Cutting plane line: A cutting plane line is heavy and shows the internal shape of a part by slicing through the object.
- Section line: Angled thin lines indicating cut surfaces in section views are called section lines.
- Leader line: Leader lines point to something on the drawing that requires clarification. The thin line is typically drawn at a 45-degree angle.