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Glossary E thru L
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Glossary Terms E thru L
ECO  (n) See engineering change order.
edge  (n) The intersection or boundary of two nontangential surfaces (faces). An edge is represented on a technical drawing as a line or a change in shading gradients in a rendered image.
edge view  (n) The view of a surface such that it is seen as a line. For a planar surface, the edge view is an orthographic view parallel to the plane in which the surface resides.
efficiency  (adj.) With respect to CAD, the speed with which software can execute a command. This is reflected in the amount of computer processing time required to execute a command.
elastomers  (n) A special class of polymers that can withstand elastic deformation, then return to their original shape and size. Natural rubber, polyacrylate, ethylene propylene, neoprene, polysulfide, silicone, and urethane are types of elastomers.
electrical engineering  (n) A field of engineering that includes the research, development, design, and operation of electrical and electronic systems and their components.
elevation drawing  (n) A type of drawing commonly used in civil, architectural, or engineering projects involving large structural layouts. An elevation drawing (sometimes called an elevation view) is an orthographic view perpendicular to the line of gravity (i.e., parallel to the terrain). These drawings are useful in planning the vertical arrangement of components within a structure, or of the structure relative to the terrain, and are also used to make aesthetic judgments since this view closely matches how the structure would be seen.
ellipse  (n) A single-curved line primitive. An ellipse is a conic section produced when a plane is passed through a right circular cone oblique to the axis and at a greater angle with the axis than the elements. An ellipse also describes a circle or circular arc viewed at any angle other than normal (perpendicular).
engineer  (n) A professional concerned with applying scientific knowledge to practical problems. The discipline is divided into a number of specialties, such as civil, mechanical, chemical, electronic, aerospace, electrical, and industrial engineering.
engineering change order (ECO)  (n) A document that begins the process for making changes in a design. Normally, the ECO will be documented in an engineering change note (ECN). A copy of the engineering drawing is attached to the order, with sketches and a written description of the change. A reference number is given to the change order so that it can be traced within the organization.
engineering graphics  (n) A communications method used by engineers and other technical professionals during the process of finding solutions to technical problems. Engineering graphics are produced according to certain standards and conventions so that they can be read and accurately interpreted by anyone who has learned those standards and conventions.
enterprise document management (EDM)  (n) See product data management.
envelope principle  (n) A term used in geometric dimensioning and tolerancing to describe how much a feature can deviate from ideal form, orientation, or position as it departs from maximum material condition.
ergonomics  (n) A technical field concerned with optimizing the interface between humans and technology. The field has numerous specialties, including industrial safety and hygiene, human–computer interface design, and the design of control panels in manufacturing plants, cars, airplanes, etc.
error bar  (n) A mark added to data points in graphs and plots to indicate the range of probable values. Since perfect accuracy is not possible in any kind of experimental method, the error bar represents the degree of certainty in the data value. The length of the bar usually represents the statistic of standard deviation.
error checking  (v) The process of evaluating actions requested by the operator to determine if such actions resulted in invalid geometry. Depending on the system, error checking may be done automatically (such as when a file is saved to disk) or manually at the request of the user.
etching  (n) The method of creating patterns, typically in metal, using chemical processes. In the electronics industry, etching is used to remove conductive material, usually copper, from printed circuit boards to create wiring patterns. The wiring pattern is printed on the board in a chemically resistant ink, and the rest of the conductive material is then dissolved away in a chemical bath.
Euler operations  (v) Low-level operations used to construct models from geometric primitives, such as vertices, edges, and faces. The validity of the model is guaranteed by a simple mathematical formula, credited to both Leonhard Euler (1707–1783) and Jules Henri Poincaré (1854–1912).
evaluated  (adj.) A description of a model for which the final form is explicitly represented in the database. An evaluated model is not concise (it may take up large amounts of memory), but it is efficient (calculations on the model are processed quickly).
exploded assembly  (n) An assembly drawing, usually a pictorial, in which the parts of the assembly are spread apart (exploded) from their functional location in order to provide a larger, clearer view of the features of the individual parts. Flow lines are used to relate the parts to each other and to demonstrate assembly. This type of assembly drawing is used extensively for technical illustrations in such applications as parts catalogs and assembly instructions.
exposure  (n) The orientation of a principal surface of an object relative to the image plane. The greater the exposure, the closer the surface(s) is to being parallel to the image plane and, therefore, the lower the distortion caused by foreshortening.
extension line  (n) A thin, solid line perpendicular to a dimension line, indicating which feature is associated with the dimension.
fabrication drawing  (n) An electronics drawing that presents the complete engineering for the manufacture of a printed circuit board. The fabrication drawing contains an accurate to scale layout of the board shape, drill hole locations, material and manufacturing specifications, and conductor pattern. The conductor pattern is broken out to make an artwork drawing, a screen print drawing, and the mask used in board etching. The drill hole information is sometimes broken out into a separate drill drawing for use in programming the drill patterns.
face  (n) A distinct planar or curved surface or region on an object. One or more faces joined together at edges define the boundary between object and nonobject. A face is a topological element in a 3-D model.
face-edge-vertex graph  (n) The data structure used by boundary representation (B-rep) 3-D solid modelers. The graph contains both geometric information on the location and size of geometric elements and topological information on how they are linked together.
facets  (n) Repeating groups of polygons of similar topology, forming an approximate representation of a curved surface. Curved surfaces such as cylinders and spheres are subdivided into a series of faceted planar surfaces, which approximate the original surface. This transformation is often used so that curved surfaces can be rendered using algorithms that only support planar surfaces.
faithful  (adj.) A measure of whether a computer model contains or imparts sufficient information to fulfill its task. In order to define the faithfulness of a model, the exact use of the model must be known.
familiar size  (n) A perceptual cue in which the known (familiar) size of an object is used to judge its distance from the observer. Often, the comparison of the perceived size of two objects is used to judge their relative locations in depth.
family of parts  (n) Similar parts that can be grouped together. A family of parts might be a series of air cylinders that have many common topologies but have variations in the geometry of certain features, such as the diameter or length of the head. Parametric techniques can be used to represent a family of parts on the computer or in drawings.
fastener  (n) A mechanical device that constrains two or more parts. Fasteners can rigidly join parts or can allow certain degrees of freedom. Some fasteners are meant to be disassembled for maintenance (e.g., screws and bolts), while others are considered permanent.
feature  (n) A general term applied to physical portions of a part. Features typically serve a function, either in the final application of the part or in the specification or manufacture of it. Examples are a hole, slot, stud, or surface.
feature control frame  (n) A rectangular outline containing geometric dimensioning and tolerancing information used in the engineering, production, and inspection of a part. The left-hand compartment inside the frame contains the symbol of the geometric control being applied. The middle compartment contains the size of the tolerance zone. The right-hand compartment contains the datum identification symbol(s).
feature of size  (n) A feature that is measurable; specifically, a spherical or cylindrical surface, or a pair of parallel plane surfaces, associated with a feature.
feature tree  (n) A computer interface element common to most constraint-based solid modelers. The feature tree lists the geometric features contained in the model in order in which they are interpreted by the modeler. New features will typically be placed at the bottom of the tree. A feature in the tree can be construction geometry, part features, or components in an assembly.
feed-through  (n) A through-hole in a printed circuit board which has a conductive surround on at least one side of the board and sometimes in the hole. The conductive pads or donuts on either side of the hole are used to make electrical connections through the board and with component wires that are soldered into the holes.
FEM/FEA  (n) See finite element modeling and analysis.
fillet  (n) A rounded interior corner normally found on cast, forged, or molded parts. Like a round, a fillet can indicate that a surface is not machine finished. A fillet is indicated on engineering drawings as a small arc.
finite element modeling and analysis (FEM/FEA)  (n) An analysis technique used extensively to model and analyze forces within a computer model or a proposed design. In the modeling phase, the continuous surface or volume is discretized into a finite number of linked primitive geometries. In the analysis phase, the model is subjected to theoretical forces applied at certain locations, and the resulting forces are calculated across the rest of the model.
first-angle projection  (n) The arrangement of the six principal orthographic projected views as commonly practiced in many countries other than the United States, including Europe. The name derives from the quadrant of three mutually perpendicular planes that define the relationship between the object, viewer, and projection plane(s).
fittings  (n) A term used to describe components that connect pipes, valves, and other fluid and gas-handling equipment. Fittings are often classified by the method used to join the components together. Some of the most common types are welded, threaded, and flanged (bolted).
fixture  (n) A rigidly held production tool that securely holds, supports, and locates the workpiece. Unlike a jig, a fixture is not used to guide a cutting tool.
flat shading  (v) A rendering method that uniformly adjusts the value of a surface color based on its orientation to the light. This method is considered the simplest shading method since it only requires the calculation of a single surface normal.
flexible manufacturing system (FMS)  (n) A group of machines that can be programmed to produce a variety of similar products. For example, an automobile parts supplier might specialize in the production of gears for transmissions. An FMS cell might be used to produce the gears for more than one automobile manufacturer because the parts are similar.
Flow charts  (n) A visualization technique or displaying relationships in time, particularly for data that doesn’t conform well to scalar mapping. PERT charts and other types of flow charts are project management tools used to map the relationship of specified project tasks, personnel, and other resources on a single timeline.
flow diagram (chart)  (n) A diagram used in electronic and piping systems to describe the system’s process and the flow of material (or electronic signals) through the proposed design. Since these diagrams only depict the functional nature of the system, they do not show the true spatial layout or geometry of the components.
flow lines  (n) Lines used primarily in technical illustrations to indicate the assembly of parts in an exploded assembly. Flow lines are thin phantom lines drawn parallel to the line of assembly between two parts. Right-angle jogs are placed in the flow line when the drawing of the part has been moved away from the direct line of assembly for reasons of clarity.
FMS  (n) See flexible manufacturing system.
focus point  (n) A location where reflecting rays from a (parabolic or hyperbolic) surface converge. Focus point describes both the physical phenomenon of light rays reflecting from a mirrored surface and the abstract geometric calculations of line paths.
fold line  (n) A basic concept in descriptive geometry used to define a line that is perpendicular to projection lines and is shared between views of a drawing. A fold line can also describe the “hinge” line between the image planes of the glass box used to define orthographic multiviews.
font  (n) The size and style of text characters.
foreshortened  (adj.) The reduction in size of one or more dimensions of a planar face due to the face not being perpendicular (normal) to the line of sight. The dimension foreshortened is defined by the axis of rotation of the face out of a plane normal to the line of sight. When the face is rotated in its edge view, the foreshortening is applied to a line.
form controls  (n) Geometric dimensioning and tolerancing methods involving the comparison of the part to perfect geometry such as straightness, roundness, cylindricity, etc.
forming  (v) A process in which components are held together by virtue of their shape. This is the least expensive fastening method, and it may or may not be permanent. Heating and air conditioning ductwork is held together by forming the sheet metal.
four-color printing  (n) A color printing process in which a full-color image is divided into four separate images, each representing the amount of one of the three subtractive primary colors (cyan, magenta, and yellow) or black contained in the image. Printing plates are made from the new images, and each is printed in a single ink color as an overlay. This process is also called the CMYK system, an acronym for the four ink colors, where K is for black.
fractal  (adj.) The term, short for fractional dimensional, used to describe graphics with randomly generated curves and surfaces that exhibit a degree of self-similarity. Fractal design tools provide new opportunities for designers to produce complex patterns with more visual realism than can be output from conventional geometry programs.
frame  (n) A single image of a longer sequence of images in an animation. Frame rate indicates the number of images shown in sequence over a unit of time, usually a second.
free-form surface  n) Three-dimensional surfaces that do not have a constant geometrical shape. Free-form surfaces follow no set pattern, are classified by their use as constrained or unconstrained, and are typically produced using sophisticated CAD programs.
front view  (n) A principal view of an object, typically the first one defined, orienting the object such that the majority of its features will be located in the front, right side, and top views.
frontal line  (n) A line that is seen in its true size in the frontal plane.
frontal plane  (n) A principal orthographic plane of projection. This plane is used to define both the front and back orthographic views.
full section  (n) A sectional view generated by passing a single cutting plane completely through the object.
functional analysis and design  (n) A design driven by the intended use of the product. Functional analysis determines if the design is an answer to the problem statement written during the ideation phase. Aesthetic considerations are often considered the foil to functional considerations.
functional gaging  (v) A type of part inspection done when specially made fixtures and devices are used to inspect parts. Also called hard gaging.
fundamental deviation  (n) A tolerancing measure used to describe the deviation closest to the basic size.
gaging tolerance  (n) The accuracy of an inspection instrument relative to the part being inspected. An inspection instrument is considered to be 'perfect' relative to the part if it is at least 10 times more accurate than the part.
gamut  (n) The range of colors possible at a single pixel on the computer monitor. The gamut is not the full range of colors perceivable by the eye but is typically quite large. The hardware and software of the computer system determine what that gamut will be.
gear  (n) A toothed wheel device that acts as a mechanical linkage to transmit power and motion between machine parts. Most gears transfer rotary motion from one shaft to another. They change the location and can change both the orientation and speed of the rotary motion. Certain gear types transform rotary motion into linear (reciprocating) motion.
gear train  (n) A mechanism consisting of two or more gears and used to transmit power. Normally, gear trains are used to do one or more of the following: increase speed, decrease speed, or change the direction of motion.
general notes  (n) Text placed in the drawing area, including general information that cannot be effectively or quickly communicated through graphical means.
general oblique  (n) A type of oblique pictorial drawing in which the two dimensions of the frontal surface are drawn parallel to the frontal plane and the third (receding) axis is drawn obliquely at any scale between 50 and 100 percent of the frontal plane dimensions. The receding axis is typically drawn at an angle of between 45 and 60 degrees.
general tolerance note  (n) Specifications on a working drawing indicating the tolerances that should be applied to a dimension if no specific tolerance is given. Usually given in the form of a note in or near the title block.
general-purpose section line  (n) A default section line symbol used to indicate the cut surface of a sectional view. This symbol is used to represent cast iron, or an anonymous material if none is defined.
generatrix  (n) A straight line for which the path through space describes ruled surfaces or solids. The path the generatrix follows is called the directrix.
geometric dimension  (n) A dimension that specifies the size and location of a feature, as well as other geometric qualities such as form and orientation. Geometric dimensioning and tolerancing, combined with statistical process control, provide a robust approach to inspection and quality control for manufactured parts.
geometric transformations  (v) Basic operations used to modify existing geometry contained in the CAD database. Examples of transformations include translation and rotation. Most transformations used in CAD systems are executed as matrix operations based on linear algebra theory.
geometry  (n) The mathematical method by which elements in space are described and manipulated. Geometry forms the building blocks of engineering and technical graphics. The term is also used to mean shape or form.
glyph  (n) A compound mark used in a visualization that cannot be classified by other commonly used marks. Glyphs are usually custom designed to encode multiple elements of data into a single mark. The objective for designing glyphs or any other marks is to tap into the innate perceptual abilities of the viewer.
Gouraud shading  (v) A rendering method that uniformly adjusts the value of a surface color based on the relationship of the light source to normals calculated for each vertex of the model. Gouraud shading is sometimes called smooth shading because the vertex normals allow interpolation of shading values across multiple polygons representing the facets of a curved surface.
graphical analysis  (n) Analytic techniques employing primarily graphics to evaluate a potential design, such as the fit of mating parts or the movement of parts in a mechanism.
graphics  (n) A mode of communication using spatial/geometric representations.
grid  (n) A regular pattern of points or lines used to help locate and orient specific marks or features or to help guide the development of sketches and roughly proportion features.
ground line  (n) In a perspective drawing or sketch, the point of the object closest to the observer.
ground’s eye view  (n) In a perspective pictorial, a viewpoint looking up at the object. From this viewpoint, the horizon line is level with the ground line of the object.
group technology  (n) The process of identifying items with similar design or manufacturing characteristics. Items with similar characteristics are grouped into part families.
guideline  (n) A type of construction line used to guide the lettering on the drawing. The term can also refer to lines used for the placement of other elements in a drawing or sketch.
half section  (n) A section view generated by passing a cutting plane halfway through an object. The result depicts half the view sectioned.
half-space  (n) A mathematically defined boundary between two regions. The term is used in constructive solid geometry (CSG) modelers to define the boundary between the solid and the void (nonsolid). Geometric primitives in CSG modelers are defined as groups of half-spaces.
halftone approximation  (n) A method of simulating varying value (gray) levels within an image when only one color of ink (usually) black is available. Dots of varying size are printed based on the average value level in the region. Because of the small size of the dots compared with the size of the image, the changes of dot size (and therefore ink density) give the impression of value changes when viewed at a distance. Halftones from full-color or gray-scale images can be created both electronically or photographically.
hardware  (n) A term used to define physical computer equipment. Examples of hardware include the monitor (CRT), keyboard, hard disk, and CPU.
height  (n) One of the three principal dimensions of an object. The height dimension is described in the right side and front views of a multiview drawing. The height dimension is often associated with the Y axis in a 3-D modeling system.
helix  (n) A 3-D curve characterized by a constant rate of curvature about two dimensions and a constant linear translation in the third. Threads on screws and bolts are helical and are classified as being either right- or left-handed.
hidden line  (n) A line used to represent a feature that cannot be seen in the current view. Like a visible line, a hidden line represents either the boundary between two surfaces (faces) that are not tangent, or the limiting element of a curved surface. A specific linestyle is defined by ANSI for hidden lines.
hidden surface removal  (v) The rendering process of removing the elements of a model not visible from a particular viewpoint. The removal is accomplished by calculating the relationship of edges and surfaces along the depth axis.
hierarchy  (n) An ordered set of elements in which each element belongs to a specific level. An element at each level can be a parent to elements below it on the hierarchy, or a child to elements above it, or both. Hierarchies are used to describe the organization of files in a computer system, or geometric primitives in a CAD model.
highway diagram  (n) See wiring diagram.
histogram  (n) A visualization technique used to summarize data by reporting the number of data points that fall within a certain range of values. Histograms are often represented as bar graphs. Because histograms provide only a summary, they depict the original information only indirectly.
hole basis  (n) A tolerancing measure used to describe a system of fits in which the minimum hole size is the basic size.
hole loop  (n) A close group of edges on the interior of an object, defining a penetration that goes part or all the way through. The number of hole loops is one of the variables in the Euler– Poincaré formula used to validate the topology of a model.
horizon line  (n) In a perspective sketch, a horizontal line marking the location where all projection lines from the observer converge.
horizontal line  (n) A line seen in its true size in the horizontal plane.
horizontal plane  (n) A principal orthographic plane of projection, used to define both the top and bottom orthographic views.
HSV color model  (n) A model based on the perceptual components of color, that is, (H)ue, (S)aturation, and (V)alue (lightness), modeled as a hexacone. Hue is laid out in a radial pattern around the hexacone, saturation ranges linearly from full saturation at the perimeter to white at the center, and value runs from the base of the hexacone (white) to the point (black).
hue  (n) The dominant spectral wavelength of a perceived color. Hue and color are often confused because the name given to the hue is often synonymous with the name of the color.
human factors analysis  (v) A process for evaluating a design to determine if the product serves the physical, emotional (aesthetic), quality, mental, and safety needs of the consumer. Specialists in human factors or ergonomics are often employed to conduct this evaluation.
human’s eye view  (n) In a perspective pictorial, a viewpoint looking slightly down at the object. From this viewpoint, the ground line is equivalent to six feet below the horizon line of the object.
hybrid modeler  (n) A 3-D modeling system that combines the operations and database structure of more than one of the commonly defined modeling systems. Used with more powerful computing systems, these modelers combine the advantages of more than one system. An example is the combination of CSG and surface modeling technology.
hyperbola  (n) A single-curved surface primitive, created when a plane intersects a right circular cone at an angle with the axis that is smaller than that made by the elements.
hypermedia  (n) An interactive, computer based information system, created with authoring tools, which allows flexible, nonlinear access. Information is linked both through elements selected within the body of the information and through sophisticated search engines.
ideation  (n) A structured approach to thinking for the purpose of solving a problem, often employing graphics. Ideation is the conceptual phase of the design process. Feasibility studies are often performed to define the problem, identify important factors that limit the scope of the design, evaluate anticipated difficulties, and consider the consequences of the design.
ideation drawings/sketches  (n) A type of freehand sketch or drawing used early in the design process to explore design ideas quickly. These sketches are usually rough and incomplete, typically not following many of the conventions used for more finished drawings.
IGES  (n) Acronym for initial graphics exchange specification, an indirect data exchange standard used largely in the United States to exchange CAD information between disparate systems. Originally developed by the U.S. government and major defense contractors, it is used mainly on workstation, minicomputer, and mainframe-based CAD systems.
illumination  (n) The amount of light energy striking a surface. Illumination helps determine how light an object surface will be perceived. The illumination model in a computer rendered scene consists of the location and types of lights providing illumination for objects being rendered.
image plane  (n) An imaginary plane on which an object is projected. The graphic representation of an object on a computer screen or paper is an example of a projection as it would appear on an image plane.
inclined edge/line  (n) An edge of a face that is parallel to a plane of projection but inclined to the adjacent orthogonal planes. The edge appears as an inclined, true-length line in one of the principal views and is foreshortened in the two adjacent views.
inclined face  (n) A planar face (surface) of an object that has been rotated about one axis from one of the principal image planes. An inclined face will appear foreshortened in two of the principal views and as an edge in the third.
independent variable  (n) A variable for which the values are controlled by the experimenter to create a response in the model as measured by the dependent variable. Every independent variable value is paired with one or more dependent variables and represents the experimental manipulation of the model.
indirect data exchange  (n) A method of translating data from one CAD system to another through an intermediate, neutral data format. Examples of intermediate data formats include IGES and DXF.
industrial engineering  (n) A field of engineering concerned with the analysis and design of systems for organizing the basic production resources such as personnel, information, materials, and equipment. Industrial engineers use mathematics, the physical and engineering sciences, and the management and behavioral sciences.
infinite light source  (n) A light source located at a theoretically infinite point in space. The sun is analogous to an infinite light source. In rendering, the user specifies an orientation for the light rays, all of which are parallel to each other.
initial graphics exchange specification  (n) See IGES.
input device  (n) Computer hardware used by the operator to input information into a software program. Examples are keyboard, mouse, scanner, etc.
instances  (n) Cloned copies of geometry already existing in a database. Typically, an instance is linked directly to the geometric and topological information of its parent but contains unique information pertaining to its location, orientation, and scale in the model/drawing. Some systems refer to instances as symbols.
integrated circuit  (n) An electronic component made up of a large number of diodes, transistors, and resisters and integrated onto a single semiconductor substrate such as silicon. An example of an integrated circuit is a central processing unit (CPU) in a computer.
intensity depth cueing  (n) A rendering technique which calculates the Z-depths of the edges in a model and sets their brightness (intensity) relative to their depths. This technique taps the aerial perceptual depth cue and has the effect of making the model fade as it goes back in depth.
interconnection diagram  (n) See wiring diagram.
interference fit  (n) A fit in which two toleranced mating parts will always interfere when assembled because the "male" part is larger than the "female" part. The resulting difference in sizes, also called the allowance, means that force is required to assemble the part. An interference fit fixes or anchors the two parts as if they were one.
International System of Units  (n) See SI.
international tolerance grade  (n) A group of tolerances that vary depending on basic size but have the same level of accuracy with a given grade. The smaller the grade number, the smaller the tolerance zone.
intersecting lines  (n) Lines that share one or more common points in space. Lines that share all their points in common, or lines for which one could be considered a subset of the other, are called coincident.
intersection  (n) The Boolean operation in which only the intersecting geometry of two solids remains.
interval scale  (n) A data scale that preserves the units used but does not have a natural zero point. Interval scales often result from the difference between two values using the same scale.
involute  (n) A curve defined as the spiral trace of a point on a flexible line unwinding from around a line, circle, or polygon. The contacting surfaces between gear teeth are designed as involutes.
irregular curve  (n) A curve consisting of multiple elements of differing degrees of curvature and/or centers. Also a specific device used in drafting to draw non-circular curved elements.
isometric axes  (n) Where the 3 axes of an isometric drawing intersect forming equal angles of 120 degrees.
isometric drawing  (n) A pictorial representation of an object rotated 45 degrees, tilted 36 degrees 16 minutes, then drawn full scale. An isometric drawing differs from an isometric projection in that all three dimensions are drawn at full scale rather than foreshortening to the true projection.
isometric ellipses  (n) A special type of ellipse used to represent holes and ends of cylinders in isometric drawings. In an isometric drawing, circular features are often not viewed normally, foreshortening them and making them appear as ellipses
isometric grid  (n) A network of evenly spaced lines drawn at 30, 90, and 120 degrees. Paper preprinted with this grid is used to sketch isometric drawings.
isometric line/plane  (n) A line or plane that is parallel to one of the principal isometric axes or to two adjacent isometric axes, respectively. Isometric lines and planes are typically the simplest elements to represent in an isometric drawing.
isometric projection  (n) An axonometric projection in which three of the axes are measured on the same scale and are at the same angle relative to each other. An isometric drawing is less pleasing to the eye than other types of axonometric projections, but it is the most common since it is the easiest to draw.
isosurfaces  (n) A surface in 3-D space that defines constant values of a dependent variable. Isosurfaces are the logical extension of contour lines (isolines), which map constant values in 2-D space. Every point on an isosurface identifies the location where three independent variable values result in the dependent variable value of interest. Like isolines, multiple isosurfaces can be used to map different dependent variable values.
italic  (adj.) A style of text in which vertical elements of letters are slanted forward. This technique is used to make words or letters visually stand out from the rest of the text.
jig  (n) A special device that holds and supports the workpiece and guides the cutting tool as the workpiece is machined. Jigs may not be rigidly held to the machine.
JIT  (n) An acronym for just-in-time, a planning strategy used to reduce cycle time and waste in production processes. JIT recognizes waste as anything that does not add value, including storing parts in warehouses. On the other hand, a production process such as drilling is a value added procedure because it increases the value of the product.
joining  (v) The bringing together of two or more parts of an assembly in such a way as to overcome the natural forces that would separate them. Joining can be done with mechanical fasteners, adhesives, etc., and can be either temporary or permanent.
joints  (n) An element in a kinematic model defining the constraints between two rigid parts of the assembly (called the links). Joints define how the links can move relative to each other, in rotation and translation.
just-in-time  (n) See JIT.
KBE  (n) See knowledge-based engineering.
key  (n) A fastening device used to attach shafts to transmit power to gears, pulleys, and other mechanical devices. Common keys are plain, gib head, Woodruff, and Pratt & Whitney. The key is placed into a groove cut into the shaft (the keyseat) and one cut into the hub (the keyway), aligning and locking the parts together. Standard keys are specified using the size of the shaft as the determining factor.
keyboard  (n) A computer input device derived from the typewriter, where keys pressed communicate discrete commands to the computer. Although most often used to input the letters of the alphabet, most keyboards contain special character keys programmed by the user or the software to perform specialized tasks.
kinematic analysis  (n) The evaluation of a design as it changes over time. Of particular interest is multicomponent mechanisms in which parts move at varying rates through different volumes of space. The positions of the parts relative to each other at various points in time are studied through kinematic analysis.
kinetic depth effect  (n) A perceptual effect in which the changing movement of 2-D patterns creates the sense of a third dimension (depth). Related to apparent motion, this effect assists in the interpretation of 3-D objects in animated sequences.
kinematics  (n) Concerned with the motion of mechanism without consideration of loads and forces.
kinetics  (n) Concerned with the effects of forces in the production and modification of motion of bodies.
knowledge-based engineering (KBE)  (n) Software systems that complement CAD by adding the engineering knowledge necessary for product design. AKBE system stores product information in a comprehensive model that is composed of design engineering rules, standardpractices, and general rules that describe how a product is designed and produced.
layering  (v) A scheme by which the various graphic elements of a drawing can be grouped together in the CAD database. This facility is used most often to control what is seen or editable on the screen and what is printed or plotted. Layering in most systems is nonhierarchical.
lead  (n) A thread term describing the linear distance a screw will travel when turned 360 degrees, or 1 revolution. Lead is closely related to the pitch of a thread.
leader line  (n) A thin, solid line used to indicate the feature with which a dimension, note, or symbol is associated. Leader lines are terminated at one end with an arrow touching the part or detail and a short horizontal shoulder on the other end. Text is extended from the shoulder of the leader.
least material condition (LMC)  (n) A tolerancing term indicating the condition of a part when it contains the least amount of material possible. The LMC of an external feature is the lower limit of the part. The LMC of an internal feature is the upper limit of the part.
left side view  (n) A principal view of an object, created by rotating the viewpoint 90 degrees about the vertical axis to the left of the front view. This view is not typically included in a standard multiview drawing.
legend  (n) The region of a visualization where an explanation is given regarding how the variables are coded. This is usually done by equating a text description to a symbol of the code. The legend is also called the key.
lightness  (n) A perceptual quality of color indicating the absolute quantity of light energy. On a gray scale, the lightest color, pure white, has the highest quantity of light. In rendering, lightness (also called value) is used to indicate the orientation of the surface to the light source.
limiting element  (n) The boundary of the projection of an object. The term is usually used to describe the edge defining the apex of a curved surface.
limits  (n) The maximum and minimum sizes shown by the toleranced dimension. The larger value in a toleranced dimension is called the upper limit and the smaller value is the lower limit.
line  (n) A geometric element that connects two points in space. Although a line itself is 2-D in nature, it may connect points in 3-D space. Lines are typically classified as either straight (linear) or curved. Lines are the most prominent element in technical drawings, defining edges of objects, indicating symmetry, relating text elements to geometric elements, creating borders, etc.
line balloon (callout)  (n) A note added to a drawing to relate an alphanumeric code with a part. A line balloon usually consists of a circle or a regular polygon enclosing the code and a leader pointing to the part. They are used extensively in assembly drawings either to directly specify a part or give an index value that references a parts list or separate catalog.
line drawing  (n) A particular type of 2-D drawing consisting of line elements, not continuous filled regions of color or shading. A traditional working drawing or blueprint would be considered a line drawing.
line graph  (n) A visualization technique, usually 2-D, in which line marks are used to indicate trends in data. In a 2-D line graph, the independent variable is represented on the horizontal scale, and the dependent variable is shown on the vertical scale. The line mark represents the mapping of the two variables.
line of sight (LOS)  (n) Imaginary rays of light radiating from an observer’s eye to the object. In perspective projection, all lines of sight start at a single point; in parallel projection, all lines of sight are parallel. LOS is sometimes referred to as the viewpoint.
line rendering  (n) A technique used in technical illustration for adding realism and readability to a pictorial drawing by altering qualities of the linework on the drawing. The thickness of the line and the positions of line breaks or gaps are altered to differentiate between geometric features of a part or assembly. Line rendering is popular because it is fast, can be done with standard drawing instruments or CAD tools, and can be reproduced by most popular reproduction techniques.
link charts  (n) A visualization technique used extensively in ergonomics to depict the spatial arrangement of controls, displays, and personnel associated with a work environment. Line marks show the connections between a worker and a control or display or in communication with other personnel. Some of the variables typically coded include frequency of usage and type of information exchange (i.e., auditory, visual, physical, etc.).
linkages  n) Rigid bodies (parts) that transmit linear or rotational force. Linkages are multiple links that are combined through joints. Constraints applied to the joints define the movement of the individual links. Common types of linkages include rocker arm, crank, lever, and four-bar.
links  (n) In a kinematic model, the geometric form representing a unique part of a mechanism. Links are related to each other through joints, which define how they can orient relative to each other.
LMC  (n) See least material condition.
local coordinate system  (n) A transient coordinate system that can be positioned anywhere in space. The local coordinate system is used to assist in the construction of geometry, and the origin is usually defined relative to the feature of current interest.
locus  (n) A graphic element representing all possible allowable locations of a point. The locus of points may be drawn as a line, circle, or arc. For example, a circle is a locus of all points at a distance from the center, equal to the radius of the circle. Loci are used extensively in geometric constructions as a tool for finding the centers of tangent arcs, the endpoints of lines, etc.
logic drawing  (n) See schematic drawing.
logic gates  (n) Electronic components that take input signals and create output signals based on the input states and the logic of the circuit. Types of logic gates include AND, OR, NAND, NOR, and inverters.
long-axis isometric  (n) A variation of the regular isometric pictorial view. In a regular isometric, it appears as if the viewer is looking down on the object from the top; in a long-axis isometric, it appears as if the viewer is looking from the right or the left of the object, with one of the axes drawn at 60 degrees from the horizontal.
loop  (n) A series of geometric elements, often referring to the elements that make up a feature profile in a 3-D model. An open loop does not close back on itself, while a closed loop does.
LOS  (n) See line of sight.
lower deviation  (n) A tolerancing term describing the difference between the minimum size limit and the basic size.





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