Alphabet of Lines

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  • Topic: Orthographic projection, Parallel projection, Isometric projection
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Alphabet of Lines

The "Alphabet of Lines" refers to the different styles of lines used in drafting to show different features about an object that is drawn. There are eleven main line types - visible, hidden, center, dimension, extension, leader, section, cutting-plane, phantom, viewing plane and break. Each line has a definite form and line weight. The standard thick line weight varies from .030 to .038 of an inch whereas the standard thin line weight varies from .015 to .022 of an inch.

Visible lines are dark and heavy lines. They show the outline and shape of an object. They define features that can be seen in a particular view.
Hidden lines are light, narrow, short, dashed lines. They show the outline of a feature that cannot be seen in a particular view. They are used to help clarify a feature but can be omitted if they clutter a drawing.

Section lines are thin lines usually drawn at a 45 degree angle. They indicate the material that has been cut through in a sectional view.
Center lines are thin lines consisting of long and short dashes. They show the center of holes, slots, paths of rotation and symmetrical objects.
Dimension lines are dark, heavy lines. They show the length, width, and height of the features of an object. They are terminated with arrowheads at the end.
Extension lines are used to show the starting and stopping points of a dimension. There should be at least a 1/16 space between the object and the extension line. Leader lines are thin lines used to show the dimension of a feature or a note that is too large to be placed beside the feature itself.

Cutting plane lines are thick broken lines that terminate with short 90 degree arrowheads. They show where a part is mentally cut in half to better see the interior detail.
Break lines are used to break out sections for clarity or for shortening a part. There are three types of break lines with different line weights. These are short breaks, long breaks and cylindrical breaks. Short break lines are thick wavy lines used to break the edge or surface of a part for clarity of a hidden surface. Long break lines are long, thin lines used to show that the middle section of an object has been removed so it can be drawn on a smaller piece of paper. Cylindrical break lines are thin lines used to show round parts that are broken in half to better clarify the print or to reduce the length of the object.

Phantom lines are thin lines made up of long dashes alternating with pairs of short dashes. Their purpose is to show the alternate position of moving parts, relationship of parts that fit together and repeated detail. They can show where a part is moving to and from. They eliminate the confusion of thinking there may be two parts instead of just one. They also show how two or more parts go together without having to draw and dimension all. They show repeated details of an object and hence, provide efficiency and less chance of drafter error.

Reference: An Alphabet of Lines. (2003). Retrieved July 21, 2011, from ViewObject.aspx?ID=mtl17903 Line Weights

Line weights, or the varying line thicknesses used in engineering drawing, are essential in creating a drawing that communicates effectively. Line weights are a vital part of conventional technical graphics language. They are embodied to the extent of being defined in national and international standards.

Line types and line weights allow drawings to communicate information that would otherwise be very difficult to convey. For example: hidden outlines, paths of motion, planes of symmetry, fictitious outlines such as major and minor diameters of screw threads, dimensions and projections, materials (hatching), and centers and imaginary intersections.

Conventional practice is that only two different line weights be used on any one drawing. This is subject to discretion and some disciplines regularly use three, and occasionally four,...
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