ONLINE GLOSSARY
0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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• CAD. An acronym meaning "Computer-aided design."
  
  
• Centerline(s). A "dividing line" defining the location of a cutting plane that precisely divides an object in half. For symmetrical objects, the centerline is the axis of symmetry. In such cases, features on either side of this line will be a mirror image of each other.
  
  
• Central Angle. The angle between the two lines that make up a pie-shaped sector of a circle. If you imagine a pizza in the shape of a circle, a sector would be a single slice. The straight edges of the slice would be two radial lines drawn from the center of the circle to the outside edge or circumference. The central angle would then be the angle between these two radial lines.
  
  
• Chordal Distance. An approximation of the distance between two points along the edge or circumference of a circle. Since the precise measurement of such distances requires utilizing mathematical formulas for the length of an arc, measuring the chordal distance is quicker and easier because it can be accomplished graphically. The chordal distance is simply the length of a straight line connecting two points along the edge of a circle. In contrast, the true distance along the circumference is the arc length between the same two points.
  
  
• Clearance. A gap created between two parts to streamline assembly and fitting. Because the proper fit of most parts requires some degree of tolerance, plans should ideally take this into account. In many cases, it is possible to draw parts in the computer much more precisely than they can be built. Creating "buffer" space around such parts provides some "wiggle room" to allow for a proper fit. In general, a margin of at least 0.01 inch or even more is often a good idea. Machine-cut parts may require less clearance, while parts cut by hand often require more clearance. See Tolerance.
  
  
• CMYK. An acronym that means "Cyan, Yellow, Magenta and Black." CMYK represents what is known as a "color space" and is the format used by printing presses and color printers to create color images using four different colors of ink. In contrast, RGB ("red, green, blue") is the method both televisions and computers use to display images on screen. Digital image files that will be printed on any sort of printer should be scanned and saved in CMYK format. This stores more information, however, and therefore takes up more computer memory than color scans saved in RGB format. CMYK images may also take longer to scan. See also Bitmap Image, Grayscale, Monochrome.
  
  
• CNC. An acronym that means "Computer Numeric Control." A CNC device is a machine that is controlled by a computer. These machines may operate in two dimensions or three dimensions to cut or shape parts out of wood, metal, or plastic. Such a device moves by means of stepper motors that are actuated by a computer-controlled interface.
  
  
• Conical Helix. A coil formed by wrapping a sloping line around a cone. This type of helix appears as a spiral when viewed from directly above. See Helix.
  
  
• Constant Cross Section. Having a cross section that does not change in either size or shape along the entire length of the object. Examples of shapes that have a constant cross section include solid rods, tubes, and pieces of pipe. An object with a constant cross section can be extruded. See also Extruding.
  
  
• Construction Lines. Temporary lines sketched on a drawing to aid in constructing views of objects. Such lines often extend from one view to another to help locate points and/or features in multiple views at the same time. Since these lines must be removed to produce a clean, final drawing, it is best to place them on a separate layer when using a computer drawing program. It is also very helpful to use a very light color for construction lines. See also Tint.
  
  
• Conventional Revolution. The practice of revolving a symmetrical object or feature until it appears true length in a particular view. For the draftsman, it may be considered poor practice to draw a true representation of certain symmetrical features in a plan view when they are not parallel to that view. The reason is simply that such objects cannot be measured when they do not appear true size in a view. While revolving such features allows them to be measured, the view in question will no longer be a true representation of what the object really looks like. As a result, this convention is somewhat subjective and may cause confusion. See also Revolution, Revolved, Revolving.
  
  
• Cross Section. A section view created by passing a cutting plane through an object. The cutting plane is typically parallel to the frontal plane of projection, though section views may also be created at any location necessary to describe the structure of an object. See also Section.
  
  
• Cube. A six-sided, three-dimensional shape where each side is a square.
  
  
• Custom Guides. Custom lines or objects in a computer illustration program that have been moved to or otherwise added to the Guides layer. Standard Guides can only be horizontal or vertical lines. Creating a Custom Guide permits the use of angled lines (such as a miter line) or other objects that have all the properties of a standard Guide, including Snap. See also Guides, Snap.
  
  
• Cutting Plane. A plane that "slices through" an object at a particular location. By plotting the intersection of the plane and the object, a cross section outline can be drawn at that location. The cutting plane is represented by a straight line in a view when the edge of the plane is parallel to that view. See also Edge View.
  
  
• Cylinder. An object with a circular cross section such as a round rod, tube or piece of pipe.

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0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Click on a letter to browse through the Glossary terms.
To download a printable version of the entire Glossary, click here.

All written content on this page © 2007 Charles Adams. ALL RIGHTS RESERVED.
Reproduction, in whole or in part, is prohibited without written permission from the publisher.