Cad Guidebook: A Basic Manual for Understanding and Improving Computer-Aided Design (58 page)

Block
See Groupings.

BOM
See Bills of Material.

Boolean
Refers to logic that compares sets or items (named after English math-
ematician George Boole). In terms of databases and searching, Boolean operators
are used to find items that meet one criteria AND another, one criteria OR an-
other, one criteria but NOT another, etc. In 3-D CAD systems, Booleans or Bool-
ean operators alter the 3-D model by joining separate solids together (as in an OR
of volumes), cutting solids (as in a NOT of volume), or intersecting solids (as in
an AND of volumes).

B-Rep
Boundary Representation. This is a basic theory for construction of
solid models based on edges, faces, surfaces. This technology is basically hidden
from the user. The 3-D CAD system may use this method, another method (such
as CSG), or a combination of them.

Byte
A sequence of 8 bits. It is used to make working with binary information
easier. There are 256 combinations of 1s and 0s in a Byte (starting from
00000000 to 11111111). Hexadecimal is usually used to work with binary data.
In hexadecimal, a Byte is just 2 characters (each hexadecimal digit holding 4 bits;
4 bits sometimes being referred to as a “nibble.”)

Glossary 289

C/C++

CAD (Computer-Aided Design)

C is a computer programming language. It was extremely popular with
the unix and PC platform until the development of GUIs. It is a compiled lan-
guage that is very efficient for managing the computer’s resources and user inter-
face. C++ (pronounced C-plus-plus) is a sort of “super-set” language for C. It
uses object oriented techniques which allows libraries of cross-functional rou-
tines to be developed which offer a higher level of abstraction versus the com-
piled C. C++ became particularly popular as GUIs were adopted.

A computer program or a system of pro-
grams that assist and enhance product development. At times, it has supposedly
meant just Computer-Aided Drafting (limiting CAD to just drawings), CADD
meaning Computer Aided Design and Drafting. However, CAD is a term that has
continued to be applied to the large software systems that automate and manage
design activities of all kinds. A CAD system does 2-D design, drawings, 3-D de-
sign, and data management. As the CAD system is integrated with other engi-
neering-related systems, they are usually referred to as CAD/CAM/CAE.

A CAD program sold by IBM for their mainframe computers. It
was the de facto CAD program for mainframe computers. It was developed by

CADAM®

Lockheed, an aerospace company.
CAE (Computer-Aided Engineering)

CAGE Code

A computer program or a system of

A computer program or a system of

programs that assist with engineering analysis. These programs use engineering
methods/formulae/algorithms to predict or estimate how products will perform.
Some of the most important types of CAE software are FEA (predicting the be-
havior of solid materials) CFD (predicting the behavior of fluids), and Dynamics
(simulating physical events such as mechanisms and impacts).

Part of the U. S. Standard Title Block. It is a number assigned by
the Federal Government to identify the type of item or business associated with
the manufacturer. It is a five character code.

CAM (Computer-Aided Manufacturing)

programs that assist and enhance manufacturing activities. Typical tasks for a
CAM system are determining how machine tools are positioned to create parts
(NC tool paths), factory floor visualization, nesting (figuring out how different
parts can be combined onto single pieces of stock for simultaneous manufacture),
and managing the various types of data generated by the software.

A high-end CAD system that is sold in the U. S. by IBM. It is devel-
oped by Dassault Systems, an aerospace company.

CDE (Common Desktop Environment)

functionality for the Xwindows GUI that is popular for the unix platform. Com-
puters from two different computer manufacturers that both use CDE would look

CATIA®

totally similar to their users.
Centerline

A set of standard appearance and

A type of Line Font that indicates the presence of circular features
in a drawing. They are lines with long solid segments and then some shorter seg-
ments. When put on a hole that is seen as a circle (not seeing the hole from the

290 Glossary

side or at an angle), then a bull’s-eye is shown where two shorter segments of the
Centerline form a cross.

CFD (Computational Fluid Dynamics)
CAE software that attempts to predict
the behavior of fluids (liquids and/or gases) for products. Because the flow of
fluids are more chaotic and nonlinear in comparison to solids, these programs
tend to be extremely specialized for particular types of problems. Thus, separate
programs would be typically be used for pump design versus compressor design
versus the flow of air around a truck body. CFD programs are often the most
computationally intensive programs a company will use. In some cases, they can
run calculations for days or weeks.

CG (Center of Gravity)
Meaningful for knowing the point in a physical object
that is at the center of the object. The object would rotate about this point. How-
ever, CG is also used to indicate the center of an area, and the center of an assem-
bly. However, more accurate terms such as centroid or center of mass should
actually be used. A 3-D CAD system can actually calculate the CG of an assem-
bly model if all the parts are modeled accurately (as solids) and assigned material
properties (or at least a density). The CAD system would find the weight of each
part by multiplying the volume of the solid times the density. Then the position-
ing of each part instance with respect to some origin would allow each part’s dis-
tribution of weight to be accounted for.

CGM File
A type of plot file or neutral graphics file. CGM stands for Com-
puter Graphics Metafile. It is generally used as a middle step between the CAD
system and specific instructions for a hard copy device. It can be used in both 2-D
plotting and 3-D model hard copy production.

Character Data
A set of data that uses text and codes. Beyond alphanumeric
data, it could contain any ASCII codes (including control codes or nonprintable
characters such as LF (Line Feed), CR (Carriage Return), ESC (Escape), etc.).
Any data in a file can be loaded as character data; however, it may not be format-
ted unless it is in an ASCII file. A single character would be a letter A, and it
would be read as a single ASCII code. A set or sequence of characters such as the
word AXIS would be called a character string or just a string. Strings may also
assume that an appropriate ASCII code be placed at the end of the string (to indi-
cate the end of the word or line of data).

Character String
See Character Data.

Client
Usually refers to a specific set of software on a workstation that is
operating as a node on a network of computers. The Client is assumed to work
with the assistance of the Server (which has other software that the Client needs
or uses). This Client/Server arrangement has meant other arrangements over the
years (particularly with respect to Xwindows). Sometimes, Client might also
refer to the entire computer on the network (although Node would be more
appropriate).

Clump
See Groupings.

Glossary 291

CNC (Computer Numerical Control)
The networking of computer controlled
machine tools in a manufacturing environment. This was an extension of basic
NC (Numerical Control) machine tools (which were not really networked to-
gether). The CNC approach allows tool-path and other specific machine opera-
tion instructions to be cataloged on server-type computers that can then download
to the machines as appropriate.

COM Card
See Aperture Card.

Compiler
A program that converts high-level programming code into low-level
instructions. A compiler is used with languages such as FORTRAN and C to cre-
ate a standalone executable file that is efficiently loaded and run by the computer.
This process becomes less clear with languages that use dynamic linking; in this
case, the high-level programming is compiled, but it becomes object code that is
later loaded on demand into Memory for use by the CPU (and converted to ma-
chine instructions as needed).

Constraint, Assembly
A constraint for part instances in an assembly model.
The constraint fixes or controls the location of the part instance with respect to
the overall assembly model or with respect to other part instances. Assembly
Constraints could be dimensions (such as a distance from one face to another, or
from one edge to a face, etc.), or geometric constraints (such as one face is per-
pendicular to another face), or logical constraints (such as one part instance is
welded to another, or a group of part instances are to be a rigid body).
Constraint, Sketching
A constraint for a 2-D sketch that is created to control
the geometry of a feature or part of a 3-D model. It could be used with a 2-D
CAD system, but they are typically only used with 3-D CAD systems. This con-
straint fixes or controls the location of 2-dimensional geometric entities (such as
line segments, arcs, splines, etc.). These constraints could be dimensions (such as
the location or size of a hole), or geometric relationship constraints (such as one
line segment is perpendicular to another), or logical constraints (such as the end
of a line is grounded or immovable).

Coordinate System
A mathematical entity that specifies the orientation of the
2-D or 3-D space. In 2-D space, a coordinate system has an X- and Y-direction
(or axis). In 3-D space a coordinate system has X, Y, and Z. The origin of the
coordinate system is where these directions have a value of 0. For a 3-D coordi-
nate system, an axis plane is formed by 2 of the 3 directions. That is, the XY-axis
plane is a plane that contains the X- and Y-direction (while Z is always 0).
CPU (Central Processing Unit)
An Integrated Circuit or chip that runs the
computer. It controls the data that is being processed and all calculations (in sup-
port of the application program).

Cross-hatching
Cross-hatching is the use of a pattern of spaced apart lines
(typically at an angle) that fills a 2-D area. This is used in a drawing to indicate
that a section of the object in the drawing has been cut open to reveal the inner
material. Thus, it is usually used with Section Views in a drawing.

292 Glossary

CSG (Constructive Solid Geometry)
A basic theory of the construction of 3-
D solid part models. This technology is really hidden from the user. The 3-D
CAD system’s operations may be based on this technique or other techniques
(such as B-Rep), and it may also allow a mixture of techniques.

Cut Plane (Cutting Plane or Cut Line)
Indicates on a drawing where objects
are cut for a Section View. It is a heavy line that has a letter shown at each end of
the line. The letter identifies the particular cut for a particular Section View.
Degrees of Freedom
DOF is associated with the constraining of sketches and
assembly models. Each element in the sketch or part instance in an assembly
model initially is able to move freely. As constraints are added, DOFs are re-
moved, and the element becomes more restricted until it cannot move. At this
point, it is considered fully constrained. DOFs are also important with mecha-
nism simulations for assembly models. In this case, DOFs that are not removed
are driven by forcing functions.

Detail
A single part that is modeled or shown in a detail drawing. It is best to
refer to them as Parts in the 3-D CAD system, however.