 Ask
the Wizard for a Glossary of Terms
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
A
AA- AA is the
abbreviation for arithmetical average. The
AA is the mean between a series of values. Compare
with RMS.
A
Chart- Pronounced A-bar chart. See also average
chart.
AOQ-
See average outgoing quality.
AOQL-
See average outgoing quality limit.
AQL-
See acceptable quality limit.
Abbe’s-
Abbe’s Law is the principle that for maximum
reliability the axis of the standard must lie along
the line of measurement.
Aberrations- Aberrations
is the term used in optics to designate what we
know as errors in linear measurement.
Absolute System- A
system of numerically controlled machining that measures
all coordinates from a fixed point of origin or zero
point.
Acceptable Quality
Limit (AQL)- The maximum percentage of defectives
that can be considered acceptable.
Accidental Errors-
See random errors.
Accumulation
of Errors- The compounding of error in serial measurements
is known s accumulation of errors. Serial measurements
are inter connected measurements whose errors are
compounded. .
Accuracy- Accuracy
is adherence to a prescribed standard. Accuracy is
comparative, whereas precision is a positive matter,
and reliability is relative. The opposite of accuracy
is "uncertainty".
Addendum- The radial
distance between the pitch circle and the top of the
tooth.
Additive Tolerances-
Tolerances that are combined by their sums. Note that
they are combined algebraically with both minus and
plus values.
Air Gaging See pneumatic
metrology.
Airy
Points- Airy points are suspension points for
a beam which allow the end surfaces to be vertical.
Note that suspension at Airy points does not provide
minimum deflection. That usually requires closer support
points.
Alignment Collimator-
An alignment collimator is a special target
(q.v.) in which the image of the target emerges in
parallel rays. See also collimation and infinity.
Alignment
Telescope- See line of sight telescope.
Allowance- The intentional
difference in the dimensions of mating parts that
provides for different classes of fits. It is a minimum
clearance (positive allowance) or maximum interference
(negative allowance) between mating parts.
Alloy- A mixture of
two or more metals fused or melted together to form
a new metal.
Ambient Temperature-
See temperature.
Amplification-
Amplification is the amount by which the senses
are multiplied in the perception of precision. It
is an increase in the output of a system as compared
to the input. Power of a system is the ratio of the
output to the input.
Angle- An angle
is the rotation necessary to bring one line into coincidence
with (or parallel to) another line in the same plane.
Complimentary angles total 90 degrees. Supplementary
angles total 180 degrees.
Angularity- The condition
of a surface axis or centerplane at a specified angle
(other than 90 degrees) from a datum plane or axis.
Anneal- To soften
metals by heating to remove internal stresses caused
by rolling and forging.
Asperities- Deviations
from perfection in surfaces are termed asperities.
The four most common types are roughness, waviness,
error of form and flaws. The first three
of these recur in a given part. Their spacings are
expressed as wave lengths. Flaws, however, are random
asperities. The roughness is considered to be the
primary texture.
Assembly Drawing-
A drawing showing the working relationship of the
various parts of a machine or structure as they fit
together.
Attribute- A characteristic
that either does or does not exist. Implies gaging.
Auto-Reflection- The
optical micrometer provides displacement of the optical
path but does not affect the angle. For angle deflection
mirrors and prisms are used. With auto-reflection
the image of a reticle is projected onto a target
which is a mirror. That image is directed back to
the telescope and the displacement between the reticle
and its reflected image is examined. This will be
a measure of angular displacement. It requires that
the telescope be provided with an illuminator. The
illuminator is often called the "lamphouse".
See also collimation.
Average
Chart- Portion of a worksheet (q.v.) showing grand
average of sampling averages.
Average
Outgoing Quality- Includes all accepted lots together
with rejected lots after they have been 100% inspected
and defectives replaced.
Average Outgoing Quality
Limit- Maximum AOQ (2.v.) for all possible incoming
qualities for a given sampling plan.
Axes- See vertical,
horizontal.
Azimuth-
For optical metrology, azimuth is a
horizontal angle measured in a clockwise direction
from the true north position.
B
Basic
Dimension- A theoretically exact value used to describe
the size, shape, or location of a feature.
Basic Size- The size
from which the limits of size are derived by the application
of allowances and tolerances.
Bias Error- Bias
error is the conscious or unconscious influencing
of measurement. See also error.
Bilateral
Tolerance- A tolerance in which variation is permitted
in both directions from the specified dimension. See
tolerance.
Boring-
An operation consisting of enlarging a hole to a specified
dimension by use of a boring bar on such machines
as lathes, jig borers, or milling machines.
Braze- To
solder with brass, an alloy made of copper and zinc.
Bridging- Bridging
is the finding of a dimension by the testing of
measurements spanning an unknown dimension and successively
closing the distance between them until the unknown
dimension is approximated.
Broach- To
finish either an exterior or an interior shape of
a workpiece using a cutting tool with a series of
teeth that gradually increase as the tool is pushed
or pulled.
Burnish- To
smooth a workpiece by rolling or sliding it over a
surface under pressure.
Burr- The
ridge or raised edge left after a machining operation.
Bushing- A
metal sleeve or lining that acts as a bearing between
rotating or moving surfaces.
C
Calibration-
Calibration determines the accuracy relationship
of a gage or an instrument to a higher standard. In
the U.S. the calibration traces the accuracy to the
National Institute of Standards and Technology (NIST),
successor to the National Bureau of Standards (NBS).
The NIST in turn coordinates the U.S. standards to
the international standards.
Caliper Measurement-
The use of any instrument that can be set to the
part feature being measured and then transfer that
setting to a standard for comparison.
Callout- A
note on the blueprint identifying a dimension, specification,
or machining process.
Cam- A sliding
or rotating part used to convert rotary motion into
intermittent or reciprocating motion.
Carburizer- Heating
a low-carbon partpiece to about 2000 degrees F (or
below melting temperature in carbonaceous solids,
liquids, or gases) and then allowing it to cool slowly
in preparation for heat treatment.
Cartesian Dimension-
A dimension between points which are parallel
or perpendicular to each other (2-D or 3-D).
Case Harden- The
process of hardening the outer surface of ferrous
alloy by heating it to a critical temperature and
then quenching in oil or water.
Centerline Average-
See roughness average.
Centerplane- The
middle or median plane of a feature.
Centralize- Movement
of instrument by feel of contact so that its axis
is oriented parallel to the line of measurement. This
is sometimes called "rocking".
Chamfer- The
flat surface formed by cutting off a sharp corner,
usually at an angle of 45 degrees.
Chase- To
cut thread in a lathe rather than with a die.
Circle- The
circle is the standard for angular measurement.
It consists of a closed, plane curve, all of whose
points are equidistant from one enclosed point, the
center. See also lobing and roundness.
Circularity- The
condition on a surface of revolution (cylinder, cone,
or sphere) where the points of the surface are intersected
by any plane perpendicular to a common axis (cylinder,
cone) or passing through a common center (sphere)
equidistant from the center.
Circular Pitch-
The length of the arc along the pitch circle from
the center of one gear tooth to the center of the
next.
Circular Runout-
The composite control of circular elements of
a surface independently at any circular measuring
position as the part is rotated through 360 degrees.
Clearance Fit-
A fit having limits of size so prescribed that
a clearance always results when mating parts are assembled.
Clinometer- A
clinometer is a very precise level.
Closed Loop- A
system in which the output of one or more elements
is compared to some other signal to provide an actuating
signal to control the output of the loop.
Coaxiality- The
condition that exists when two or more features have
coincident axes (i.e., a feature axis and a datum
feature axis).
Collimation- Collimation
means to render parallel. Light rays emanating from
a source diverge. A collimator directs them
into parallel rays. See also infinity. An alignment
collimator is a target using collimation.
Command Loop-
An input signal or an external signal to which
the servo must respond.
Comparator- Both
indicators and comparators are sensing elements in
systems that measure by comparison. The unknown is
compared to a standard. Indicator is the term
applied to the lower precision instruments such as
dial indicators. Comparator is the term applied
to the higher precision instruments. These may be
either mechanical or electronic, but are chiefly electronic.
For greatest reliability these instruments should
be used only to compare, not to measure directly.
Their greatest accuracy is at the zero reading. The
further from zero, the greater the error they add.
A test indicator is the least precise version,
and is used only for rough setup, etc.
Comparison Measurement-
Comparison measurement is measurement with
an instrument that detects the difference between
the part and a separate standard. See also direct
measurement.
Complimentary
Angle- See angle.
Component- A
single unit or part.
Compound Angle-
Compound angles are formed by the edges
of triangles that lie in different planes. Face
angles are formed by the intersections of edges
of solids. Dihedral angles is the opening between
planes.
Concentric- Having
a common center, such as circles or diameters.
Concentricity-
A condition in which two or more features (cylinders,
cones, spheres, hexagons, etc.) in any combination
have a common axis.
Constant Interval
Sampling- Sampling based on the sequence at which
parts leave a production operation.
Construct- To
create new elements with previously measured or constructed
elements.
Contour- The
literal meaning of contour is the outside outline
of any shape. In practice, however, it has come to
mean the irregular outlines that cannot be conveniently
defined by combinations of straight lines and area
of regular radii.
Contour Tolerancing-
See profile of a line or profile of a surface.
Control- A
device used to regulate the function of a unit.
Control Charts-
Charts that facilitate visual analysis of production
trends. Each contains separate average chart and range
chart.
Coordinates- A
set of numbers uniquely defines a position or point
in space.
Coordinate Measuring
Machine- Coordinate measuring machines are
instruments that locate point coordinates on three-dimensional
structures while simultaneously integrating both the
dimensional and orthogonal relationships. CMMs are
chiefly used for plate work (q.v.) on relatively
large parts. They are available in a large variety
of sizes and configurations.
Cosine Error,
Sine Error- The cosine error is induced
by lack of squareness between the feature of the part
and the measurement instrument. The sine error
results from misalignment of a flat contact with
the part feature.
Counterbore- The
enlargement of the end of a hole to a specified diameter
and depth.
Countersink- The
chamfered end of a hole that receives a flat head
screw.
Cylindricity-
A condition of a surface of revolution in which
all points of the surface are equidistant from a common
axis.
D
DCC-
Direct Computer Control
DCC Position Point-
To move the probe tip an absolute or incremental
distance to a predetermined position through data
input.
Datum- A point,
line, plane, cylinder axis, etc., assumed to be exact
for purposes of computation or reference and established
from actual features. From the datum the location
or geometric relationship of other features of a part
may be established.
Datum Axis- The
theoretically exact centerline of the datum cylinder
as established by the extremities of contacting points
of the actual datum feature cylindrical surface or
the axis formed at the intersection of two datum planes.
Datum Feature-
A feature (hole, slot, diameter, etc.) used to
establish a datum. It refers to the actual part surface
of the feature coincidental with or relative to a
datum.
Datum Identification
Symbol- The datum reference letter drawn in a
rectangular box.
Datum Line- A
line that has length but not breadth.
Datum Plane- A
theoretical plane established by extremities of the
actual feature with a reference plane.
Datum Point- A
point that has position but not extent.
Datum Reference-
A datum feature as specified on a drawing.
Datum Reference
Frame- A system of three mutually perpendicular
datum planes or axes established from datum features
as a basis for dimensions for design, manufacturing,
and verification. It provides complete orientation
for the feature involved.
Datum Surface-
A surface or feature (hole, slot, diameter, etc.)
that refers to the actual part surface or feature
coincidental with or relative to a datum and/or used
to establish a datum.
Datum Target-
A specified point, line, or area on a part used
to establish a datum.
Decimal-inch System-
The decimal-inch system is the customary
inch-pound system in which the inch has been divided
into decimals in order to avoid fractions that are
awkward in calculations.
Dedendum- The
radial distance between the pitch circle and the bottom
of the tooth.
Degradation of
Workmanship- Degradation of workmanship
is the generalization that no part feature is as accurate
as the process or machine that produced it. Thus,
the less dependent a part feature is on previous operations,
the greater the probability of accuracy.
Depth of Focus-
Depth of focus depends upon the numerical
aperture (N.A.) as well as the magnification and is
inversely proportional to both. The higher the magnification
the shorter the depth of focus for any given numerical
aperture. Also known as depth of field.
Design Size- The
size from which the limits of size are derived by
the application of tolerance. When there is no allowance,
the design size is the same as the basic size.
Detail Drawing-
A drawing of a single part that provides all the
information necessary for the production of that part.
Diascopic Projection-
Diascopic projection is the term for projection
of transparent objects, such as film. See also episcopic
projection.
Die- A tool
used to cut external threads by hand or or machine.
Also, a tool used to form or cut a desired shape.
Die-Casting- A
method of producing castings using molten metal under
pressure and injecting it into a suitable steel mold.
Die-Stamping-
A partpiece cut out by a die.
Digital/Analog-
A digital instrument displays the measurement
in numerals. In an analog instrument a moving member
(a "hand") moves in proportion to the change
in measurement, therefore it replicates the measurement,
but greatly amplified. In general, digital readouts
are desirable to show limits, whereas analog readouts
are best when trends are to be followed. Most analog
instruments use dial scales for readout.
Digital Readout-
(DRO) – Interfaces scales/readerheads, interfaces
probe to computer and displays X, Y and Z axis location
relative to object or machine coordinate.
Dihedral Angle-
The dihedral angle is the opening between
planes. See also compound angle.
Dimension- A
numerical value expressed in appropriate units of
measure and indicated on a drawing.
Dimensional Metrology-
See linear metrology.
Direct Measurement-
Direct measurement is measurement with
an instrument that incorporates its standard. See
also comparison measurement.
Discrepancy- See
uncertainty.
Discriminating
Power- Measure of performance of sampling plans.
Discrimination-
Discrimination is the fineness of the scale
divisions of an instrument. It is the smallest division
of the scale that can be read reliably. As discrimination
is incresed the range is decreased. The ratio for
this varies among the types of instruments.
Displacement Method-
Displacement method is a method of measurement
in which each end of the part feature is separate
compared to a standard. There is a displacement in
getting from one end to the other. It is the relationship
between the distance displaced and the standard that
constitutes the measurement.
Distance Dimension-
Defines a distance between two elements as selected
by the operator.
Dividing Heads-
Dividing heads are mechanical devices for
dividing a circle into angular portions.
Dowel Pin- A
pin anchored in one partpiece and fitting into a hole
in an abutting partpiece to prevent motion or slipping
or to keep the pieces accurately located in the relative
position.
Draft- The
angle or taper on a molding pattern or casting that
permits withdrawal from the mold or forming die.
Drill- To
cut a cylindrical hole with a drill or a pointed tool
rotated under pressure.
Drop-Forging-
Formation of a partpiece between dies by the use
of a drop hammer.
Dynamic Measurement-
Most linear measurement is static. It is
performed on something that is stable and unchanging,
at least over a short period of time. Dynamic measurement,
in contrast, is the continuous monitoring of a changing
quantity. Although there are many exceptions, digital
readouts are associated with static measurement and
analog readouts are associated with dynamic measurement.
E
Eccentric-
Not having a common center. Also used to describe
a device that converts rotary motion into reciprocating
motion.
Eccentricity Error-
Eccentricity Error is discrepancy in angular
measurement caused by the measurement arc not being
concentric with the center of rotation.
Element- A
detail of a work piece: plane, circle, etc.
1 – D – Point
2 – D – Line, Circle,
Eclipse
3 – D – Plane, Cylinder,
Cone, Sphere
Elongated Hole-
A hole that has been enlarged on two sides.
Enclosure- A
rectangle drawn around a component to indicate the
limits of an assembly.
End Standards-
End standards are special gage blocks that
are placed on ends of stacks of gage blocks to convert
to other measurements than the normal external end
measurements of the stacks.
Episcopic Projection-
Episcopic projection is the term for optical
projection of opaque objects. See also diascopic
projection.
Error- Error
is the difference between the measured value and
the true value. Error always exists although it may
not be measurable. Observational error is formed
during the reading of an instrument. Parallax error
is caused by apparent shifting of objects when
the viewing position is changed. Manipulative error
is caused by the handling of the instrument and
the part. Bias error is the conscious or unconscious
influencing of measurement. See also systematic
error, random error and illegitimate error.
Execute Program-
To run a program.
Extrusion- The
process of shaping metal by forcing it in the hot
or cold state through dies of the desired shape.
F
Face-
To machine a flat surface.
Face Angle- Face
angles are formed by the intersections of edges
of solids. See also compound angle.
Feather- A
flat sliding key.
Feature- Specific
characteristics of component portions of a part that
may include one or more surfaces such as holes, threads,
profiles, faces, or slots.
Feature Control
Symbol- A rectangular box containing geometric
characteristic symbols and the form or position tolerance.
Feature of Size-
One cylindrical or spherical surface, or a set
of two plane parallel surfaces, each of which is associated
with a dimension. A feature such as a hole, shaft,
pin, or slot that has an axis, centerline, or centerplane
when related to geometric tolerances.
Feedback-
Output signal from a feedback element.
Feel- Feel
is the perception of the distortion that results
from physical contact between the instrument and the
part or standard.
Field of View-
In an optical system the field of view is
the screen diameter divided by the magnification.
File- A tool
that has sharp cutting points or teeth used for abrading
or smoothing other surfaces.
Fillet- A
concave surface or filling at the intersection of
two surfaces that provides added strength.
Fin- A thin
projected edge or casting.
Finish- A
surface specification.
Fit- The general
term used to specify the range of tightness or looseness
as a result of a specific combination of allowances
and tolerances in the design of mating part features.
There are four fits: clearance, interference, transition,
and line
Flatness- The
condition of a surface having all elements in one
plane.
Folded Optics-
Folded optics refers to the use of mirrors
or prisms to realign optical paths so that instruments
may be of compact size.
Form Tolerancing-
Permitted variation from the perfect form indicated
on the drawing.
Freedom- There
are six possible degrees of freedom. Three
are translational and involve movement in the X, Y
and Z axes. The other three are rotational about these
axes. If movement in any of these degrees of freedom
is prevented it is said to be constrained. See also
orthogonal.
Fringe Bands-
Fringe bands are the alternate light and
dark stripes that result when two rays combine and
interference takes place.
Fringe Patterns-
Fringe patterns are groups of fringe bands.
Fuller- A
hammer used for forming grooves and spreading hot
iron under hammer blows.
Full Indicator
Movement- (FIM, FIR, and TIR): FIM refers to full
indicator movement during one full revolution of the
part about its datum axis. FIR refers to full indicator
reading. TIR refers to total indicator reading.
Full Indicator
Reading- (FIR, TIR, and FIM): The total indicator
movement observed with the dial indicator in contact
with the part feature surface during a full revolution
of the part about its datum axis. (Use of the international
term FIM is recommended.) Also refers to the reading
observed while in traverse over a fixed noncircular
shape.
G
Gage
Blocks- Gage
blocks are the mass produced end standards that
combine arithmetically to form usable length combinations.
They are standards that re traceable to the national
bureau of standards in the countries of their use.
Gage, Gauge- Gauge
is the spelling used in Great Britain but finds some
use in the U.S. It is chiefly found for nonlinear
measurement instruments (fluid gages, etc.). However,
it is finding increased use for coordinate measuring
machines where it designates a device with a proportional
range and some form of indicator.
Gages, Snap- A
snap gage is a caliper type device that
has been preset to a given dimension. Often made with
two settings, one to admit acceptable parts, the other
to reject out-of-tolerance parts. This general class
is known as attribute gages and are frequently
called "go and not-go" gages or "go/not-go"
gages. They are also called "limit"
gages. See also go/not-go gaging.
Gaging- Gaging
is single-purpose measurement to determine if
objects are between size limits or to sort objects
into size categories.
Galvanize- To
coat a metal surface with zinc as a protection against
corrosion.
Geometric Characteristics-
The basic elements that form the language of geometric
dimensioning and tolerancing.
Geometric Dimension-
A dimension between two elements which takes into
consideration the specific conditions of an element.
Geometric Optics-
Geometric optics is the technique for ray
tracing. See also ray tracing.
Go/Not-Go Gaging-
A go gage accepts all properly sized parts.
If a female part is not accepted it is too small.
If a female part is accepted by the not-go
gage, it is too large. The reverse applies to male
parts. See also snap gages.
Graduate- To
mark in regular degrees of measurement, as on a scale
or dial.
Grinding- A
machine operation that consists of finishing a metal
surface by means of abrasives.
Gusset- An
angular piece of metal fastened to reinforce or strengthen
a partpiece or assemblies.
H
Hard/Fixed
Probe- A
non-deflecting manual probe tip.
Hardness Test-
Techniques used to measure the degree of hardness
of heat-treated materials.
Heat Sink-
A heat sink is a body with rapid heat transfer
on which workpieces and gages can be placed to arrive
at the same temperature before measurement. The process
is known as "normalizing". See also
temperature.
Heat Treatment-
The application of heat to metals to produce desired
qualities of hardness, toughness, or softness.
Histogram- Graphical
representation of a frequency distribution in which
one dimension is proportional to the range of frequencies
and the other dimension is proportional to the number
of frequencies appearing within the range. See also
normal distribution curve.
Hobbing- A
special gear-cutting process in which the gear blank
and hob rotate together as in mesh during the cutting
operation.
Home Position-
Defines absolute zero-location relative to machine
coordinates.
Hone- A method
of finishing a hole or other surface to a precise
tolerance.
Horizontal- See
vertical.
Hub- The central
part of a wheel.
I
Illegitimate
Error- Whereas
the other common errors must be assumed to exist to
some extent, illegitimate errors should never occur.
They are accidents, the avoidable mishandling of some
portion of the measurement act. See also errors,
systematic errors and random errors.
Image-
Light rays passing through a lens converge on a point
known as an image. Such rays originate at an
object. Together they are known as conjugate
points. For a convergent lens (convex) a real
image is formed. For a divergent lens (concave)
a virtual image results. The real image lies
on the side of lens away from the object and is inverted.
The virtual image lies between the lens and the object
and is erect.
Implied Datum-
An unspecified datum whose influence on the application
is implied by the dimensional arrangement on the drawing
(e.g., the primary dimensions are tied to an edge
surface, and this edge is implied as a datum surface
and plane).
Inch-Pound System-
The inch-pound system is the conventional
measurement system for the United States and Great
Britain. Based on the foot, pound, second, degree
Fahrenheit, ampere and candela.
Incremental System-
A system of numerically controlled machining that
refers to the preceding point when making the next
movement.
Index Heads- Index
heads are mechanical devices for dividing a circle
into angular portions. Also known as dividing heads.
Indexing- Indexing
is the act of measurement of angles or setting
out angles for machining by use of a rotary table.
Indicators- See
comparators.
Infinity- In
metrology infinity has a special meaning. It
is the distance from which rays reaching the observer
are parallel. See also collimation and zenith
sight.
Inspection- Inspection
is the verification of conformity to a standard,
generally applied to the production of goods, but
also used for remedial examination.
Interchangeability-
The condition that ensures the universal exchange
of a mechanism or assembly.
Interchange Method-
The interchange method is a method of measurement
in which both ends of the unknown feature are compared
with both ends of a standard of the desired dimension,
or to a ruled scale. It is known as measurement
by comparison.
Interference Fit-
Interference fit refers to parts that must
be compressed to mate.
Interferometer-
An interferometer is any instrument making
an application of interferometry. See also interferometry.
Interferometry-
Interferometry is the formation of visible
bands of light by interacting wave fronts. Interferometry
is used for precise comparisons using gage blocks
and for surface evaluation. Interferometry is also
the basis for precise optical metrology instruments
such as the pointing interferometer.
Intermediate Point-
A position point in a DCC program to assure probe
tip path clearance between two measured points.
International
Inch- The international inch is the reconciliation
of the inch to the meter. One inch equals
25.4mm.
Interpolation-
Interpolation is the selection of the nearest
graduation when a measurement lies between. The observational
equivalent to the rounding off (q.v.) process
in computation.
Interrelated Datum
Reference Frame- A reference frame that has one
or more common datums with another datum reference
frame.
Involute- A
spiral curve generated by a point on a chord as it
unwinds a circle or a polygon.
J
Jig-
A device used to hold a part to be machined and to
position and control (guide) the cutting tool.
Jig Transit- A
jig transit is similar to a surveyor’s transit,
but it does not have scales for measuring angles.
It has, however, provisions for both autocollimation
(q.v.) and optical projection. Its most important
feature is that the elevation axis is hollow. This
allows two lines of sight perpendicular to each other
to intersect on the azimuth (q.v.) of the instrument.
Also known as optical transit square and jig level.
See also tachymetry.
Johansson, C.E.-
Johansson was a pioneer in metrology and clearly
anticipated modern, interchangeable gage blocks. More
importantly, he understood the significance of this
development.
Joy Stick Control-
A joy stick control allows the operator
to control the direction of travel of the moving member
in two orthogonal axes, as well as the rate of travel.
It is regularly used for manual operation of CMMs.
See also coordinate measuring machine.
K
Kerf-
The lit or groove left by a saw or cutting tool.
Ket- A bar,
pin, or wedge used to prevent rotation of a gear or
pulley on a shaft.
Keyseat- The
groove that holds the key in position, as in a shaft.
Knurl- The
process of marking the surface of a part by rolling
depressions in the surface, usually for better hand
grip.
Krypton 86- Krypton
86 is a gas which, when electrically excited,
emits the wave length of light which is the basis
for the international standard. It was selected because
of its stability. However, it is more practical to
use helium gas to emit light for most practical work.
L
LQ-
See limiting quality protection.
Lap- To finish
a surface with a very fine abrasive impregnated in
a soft metal.
Laser- A laser
emission is an intense, narrow beam of light that
is of a single wave length (color). The beam will
travel great distances with little loss of energy
and only small dispersion. Warning: A laser beam can
damage eyesight or blind. Never look directly into
the beam. Laser instruments are similar to conventional
ones except for the laser light source and the use
of photoelectric sensors. See also photoelectric
instruments.
Layout- Layout
is the use of measurement instruments to mark
features on workpieces for subsequent machining. Limited
to rough machining, the final machining is controlled
by machine control settings and verified by measurement.
Least Count- The
least count is the discrimination of a vernier
instrument.
Least Material
Condition (LMC)- The condition of a part feature
that contains the least amount of material possible
(e.g., largest hole size and smallest shaft size).
Level- The
level is an instrument for establishing a horizontal
line. By means of two or more such lines intersecting,
a horizontal plane may be established. The standard
for a level is gravity. Very precise levels are known
as clinometers.
Light- Light
is the electromagnetic energy radiation in frequencies
to which the human eye is sensitive, as well as those
of slightly longer and slightly shorter wave lengths.
See also light rays and ray tracing.
Light Rays- Light
rays are imaginary lines perpendicular to wave
fronts. Althought they do not physically exist they
are a convenience in tracing the passage of light
through an optical system. See also rays and ray tracing.
Light Wave- A
light wave is the pulsation in space that transmits
light energy. A wave front is an advancing pulse of
energy. See also light.
Limit Dimensioning-
A method of dimensioning in which only the maximum
and minimum dimensions are specified.
Limiting Constants-
Factors for determining control limits.
Limiting Quality
Protection- The worst quality that can be accepted.
Limits of Size-
The applicable maximum and minimum sizes of a
feature.
Line of Collimation-
See line of sight.
Line Fit- A
fit having limits of size so prescribed that surface
contact may result when mating parts are assembled.
Line-of-Sight-Telescope-
In practical work the point on the object being
examined at the intersection of the reticle’s lines
is on a line called line of sight or line
of collimation. It is absolutely flat and straight
in undisturbed air. It may be used as a reference
rom which measurements are made. The simplest optical
alignment instrument is the line-of-sight telescope.
This type of telescope establishes optical lines of
reference. With optical micrometers they provide a
limited measuring range. With the addition of the
micrometers these instruments become known as alignment
telescopes. See also optical micrometers.
Linear Metrology-
Linear metrology is related to measurements
taken along a line. In general use it includes measurement
along curved lines as well as straight lines and angles.
It applies to areas and volumes because these can
be reduced to their component lines. Often referred
to as dimensional metrology.
Lobing- Lobing
is deviation from roundness. It is to a round
surface what waviness is to a flat surface. See also
roundness.
Location Tolerance-
A statement of how far an actual feature may vary
from the perfect location implied by the drawing as
related to datums or other features. Expressions of
location tolerances refer to the category of geometric
characteristics containing position, concentricity,
and symmetry.
Logarithms- The
term logarithms is generally used to mean "common
logarithms". These are the exponents to which
ten must be raised to equal the number. For example,
the logarithm of 100 is 2 because 10 sq. = 100. The
logarithm of 23 is 36173 because 10 .36172 = 23. Logarithms
facilitate the expression and calculation of complex
values.
LURD- LURD
is a convention for expressing measurement changes
to minimize misunderstandings. It stands for: left,
up, right, down.
M
Machine
Coordinates- Defines
the X,Y,Z location of the machine and/or probe tip
relative to the machine geometry.
Macrogeometry-
Macrogeometry means large scale consideration
of form or shap. In popular usage macrogeometry is
concerned with size and shape that can be expressed
with standard inspection instruments. Evaluation of
squareness in shop machines usually is macrogeometry.
Macrometrology-
Macrometrology refers to large scale work
such as the setup of large machinery, ship building,
land surveying, etc. See also macrogeometry.
Magnification-
The total magnification is the product
of the eyepiece magnification and the objective magnification.
The eyepiece magnification is usually X10. Thus coupled
with an objective of X43 the total magnification would
be 430 power.
Manipulative Error-
Manipulative error is error caused by the
handling of the instrument and the part. See also
error.
Margin of Safety-
In a measurement it means the amount that the
measurement process exceed the required minimum accuracy
and/or precision.
Master Flat- A
master flat is an optical flat having surfaces
of maximum precision. It is used to calibrate working
flats. See also optical flats.
Mastering- Mastering
means setting to standards. Although it can apply
to all types of measuring systems it is chiefly applied
to pneumatic metrology.
Material Condition-
An outside edge is less than 180 degrees of material.
An inside edge is more than 180 degrees. These are
the material conditions. When material is dimensioned
the part feature is male. When the space between material
is dimensioned the part feature is female.
Maximum Dimension-
The largest acceptable limit.
Maximum Material
Condition (MMC)- The condition of a part feature
that contains the maximum amount of material possible
(e.g., minimum hole size and maximum shaft size).
Maximum True Position-
The condition of a part feature at MMC located
at the limit of the specified true position tolerance
one. It represents the worst condition of assembly.
Measure- An
element of reference used for quantitative comparison.
Measured Point-
The measured point is the point on a scale
that coincides with the end of the feature being measured
opposite from the reference point. See also reference
point.
Measurement- Measurement
means to proportion by measured lots. The measurement
may be any quality (length, weight, hardness, ertc.)
and lots may be in any units (inches, volts, picas,
etc.) See also metrology.
Measuring Speed-
The speed or velocity by which the probe approaches
an element about to be contacted.
Median Plane-
The middle or centerplane of the feature.
Memory Device-
A memory device is a means for retaining
a reading mechanically so that it will not be lost.
Usually a simple clamp. The term is also used for
the memory capability of some electronic measurement
instruments.
Metric System-
The familiar name for System International d’Unites,
the most recent of many so called metric systems.
Often abbreviated "St." Based on the meter,
kilogram, second, degree Celsius, ampere and candela.
Metrology- Metrology
is the science of measurement. See also measurement.
Metrology Laboratory-
A metrology laboratory is a laboratory
for the calibration of standards. May be a department
within a company or an outside service.
Microgeometry-
Microgeometry means small scale considerations
of form or shape. The precision in microgeometry is
expressed in mikes. Evaluation of surface finish and
flatness of gages is microgeometry.
Micrometer Instruments-
Micrometer instruments are measurement
instruments that achieve their amplification as a
result of the resolution of screw threads.
Micrometrology-
Micrometrology refers to very small work,
smaller than encountered in most shop work. See also
microgeometry.
Microscope- A
microscope is an instrument for greatly enlarging
the view of a part feature. That capability is known
as amplification (q.v.). Whereas most measurement
systems alter their measurements to a considerable
degree, optical systems do not impose those limits,
but they have other problems.
Mike- In the
decimal-inch system of terminology, mike means
millionths. However, in popular use "micro-inch"
(with or without hyphen) is the most common designation
for millionths of an inch.
Mil- In the
decimal-inch system of terminology, mil means
thousandths.
Mil-STD-105- The
standard for sampling required for most Department
of Defense applications.
Minimum Dimension-
Opposite of maximum dimension.
Minimum Material
Condition- See Least Material Condition. See also
tolerance.
Modifier- The
term used to describe the application of the MMC or
the RFS principle.
Monochromatic
Light- Monochromatic light consists of
one wave length (color) only.
Multiple Datum
Reference Frames- More than one datum reference
frame on one part.
N
National
Institute of Standards and Technology (NIST)-
New name for National Bureau of Standards.
National Bureau
of Standards (NBS)- Former name for National Institute
of Standards and Technology, the official standardization
agency for the government of the United States.
Natural Capability-
The natural capability of a process is
range of the resulting part sizes that can be expected
during normal operation. It is the basis for statistical
quality control by variables (q.v.).
Natural Functions-
See trigonometry.
Nominal Size-
The stated designation used for general identification.
Nonferrous- Not
derived from an iron base or an iron alloy base (e.g.,
aluminum, magnesium, and copper).
Normal- Probe
tip direction is perpendicular to the element being
probed.
Normal Distribution
Curve- The normal distribution curve is
the bell shaped curve that results when a variable
is changing by chance, such as the throws of dice.
It is called a histogram. In the same manner
any production process may be graphed. See also standard
deviation.
Normality- See
perpendicularity.
Normalize- See
heat sink and temperature.
Normalizing- A
process in which ferrous alloys are heated and then
cooled in still air to room temperature to restore
the uniform grain structure free of strains caused
by cold working welding.
Numerical Aperture
(NA)- The higher the NA the greater the
resolving power (q.v.) The NA is = n sin u where n
is the lowest refractive index that appears between
the objective and the front lens of the objective,
and is half of the angular aperture of the objective.
Fortunately, it is marked on lens mounts.
O
Object
Coordinate(s)- Defines
the location the machine and/or probe tip relative
to the part geometry.
Observational
Error- Error formed during the reading of an instrument.
See also error.
Off-Axis Error-
When measuring a curved surface, the true value
is found only when the measuring axis is in line with
the center of curvature. Any deviation is called off-axis
error.
Operating Band-
The acceptable range based on the standard values.
Operating Characteristic
Curves- Operating characteristic curves are
a graphical means for comparing sampling plans. They
enable SQC plans to be compared. They show the relationship
between lot size and number of defectives.
Operator Text-
Text output to screen only as instructions for
the operator.
Optical Alignment-
Optical alignment is that branch of metrology
that uses light waves to examine sizes and geometrical
relationships over larger distances than ordinarily
required in shop and laboratory work.
Optical Comparator-
An optical comparator is an instrument
that projects a greatly magnified image of a part
feature onto a screen for examination.
Optical Flat-
An optical flat is a glass or quartz reference
surface with one or both sides finished to be precisely
flat and to have minimum surface imperfections. Flats
is the general term for such devices made from nontransparent
materials such as steel or ceramics. A master flat
has surfaces of maximum precision. It is used to calibrate
working flats.
Optical Micrometer-
An optical micrometer is a mechanically
adjustable means to offset an optical path in one
axis. It is calibrated so that the offset may be known.
Optical micrometers are frequently used in pairs at
right angles to each other. They are not used alone
but are incorporated into instruments such as the
line of sight telescope. Note that the optical micrometer
does not affect the angle of the optical path, only
its displacement.
Optical Polygons-
Optical polygons are polygons with precisely
spaced faces that represent divisions of a circle.
In other words, they represent angles. They are used
with optical alignment instruments to set out and
to measure angles.
Optical Square-
An optical square is a means for turning
all or some of the rays in the optical path to 90
degrees from that path.
Orientation Tolerances-
Tolerances applicable to related features where
one feature is selected as a datum feature and the
other is related to it. Orientation tolerances are
perpendicularity, angularity, and parallelism.
Orthogonal- Orthogonal
literally means rectangular or right angled. In
popular use it has come to mean movement in two or
three axes at right angles to each other.
Orthogonal Array-
Orthogonal array refers to a device in
which the functional parts act at right angles to
each other.
Orthographic Projection-
A multiview drawing that shows every feature of
a partpiece in its true size and shape.
Overhang- The
unsupported portion of an instrument. Always to be
avoided.
P
Parts
Program- See
program.
Parallax Error-
Parallax error is apparent shifting of
objects when the viewing position is changed. See
also error.
Parallel Separation
Planes- Parallel separation planes are
a concept that simplifies measurement with optical
flats. The concept consists of a set of planes parallel
to the working surface and one-half wave length apart.
Their intersection with the part is seen as fringe
bands.
Parallelepiped-
The shape of a tolerance zone. The term is used
to describe total width and to describe geometrically
a square or rectangular prism or a solid with six
faces, each of which is a parallelogram.
Parallelism- The
condition of a surface, line, or axis equidistant
at all points from a datum plane or axis.
Perpendicularity-
The condition of a surface, axis, or line 90 degrees
from a datum plane or a datum axis.
Photoelectric
Instruments- In order to avoid the subjective
bias of the observer, opotical instruments have been
developed that use photoelectric sensors to
ascertain the reference and measured points. The most
advanced of these use lasers as their light source.
See also laser.
Pilot Hole- A
small hole used to guide a cutting tool for making
a larger hole.
Pinion- The
smaller of two mating parts.
Plan View- The
top view of a partpiece.
Plate Work- See
surface plate.
Pneumatic Metrology-
Pneumatic metrology refers to any measurement
system that uses pressure changes in a fluid (air
or other gases) system to amplify changes in part
sizes or shapes. Pneumatic gages are basically analog
devices.
Polar Chart Method-
See V-block method.
Polar Dimensions-
A dimension defined by distance and an angle.
Position- Defines
a dimension of one element as selected by the operator
relative to the active alignment system part zero.
Positional Tolerancing-
Positional tolerancing recognizes that
the limits of clearances and fits between parts occur
in circles, not the rectangles that result from tolerancing
with orthogonal relationships (q.v.). This allows
tolerances to be widened without loss of reliability.
See also tolerance.
Positioning Speed-
The speed of the probe tip as it traverses between
probe-speeds.
Precision- Precision
refers to the fineness of readings or dispersion
of measurements. Precisiion is a positive matter,
whereas accuracy is comparative and reliability is
relative.
Precision Instruments-
Precision instruments are those providing
amplification of the natural sense of sight and touch.
Primary Alignment-
Levels the part. Defines spatial orientation of
the part.
Print Text- Comments
or explanations inside a program to clarify dimensions.
Probe Head- An
intricate assembly which carries the touch probe and
probe tips and attaches to the Z-axis assembly.
Probe Point Deviation-
Defines the location of a measured point relative
to a geometrically perfect form numerically.
Probe Speed- The
speed of the probe tip as it approaches an element
about to be contacted.
Probe System-
An assembly of one or more probe tips.
Probe Tip- A
single element of a probe assembly which is used to
touch the surface of a feature on the part.
Profile- To
machine an outline by moving a small rotating cutter
usually controlled by a master cam or die.
Profile of Any
Line- The condition permitting a uniform amount
of profile variation, either unilaterally or bilaterally,
along a line element of a feature.
Profile of Any
Surface- The condition permitting a uniform amount
of profile variation, either unilaterally or bilaterally,
on a surface.
Profile Tolerance-
Tolerance that controls the outline or shape of
a part as a total surface or at planes through a part.
Program- A
sequence of steps which the computer can follow to
do a task.
Projected Tolerance
Zone- A tolerance zone applied to a hole in which
a pin, bolt, screw, etc., is to be inserted.
Protocol- Printed
results of dimensions.
Protractor- A
protractor is an instrument for measuring angles
by the displacement method. They usually have calibrated
arcs as standards.
Q
Quenching-
Cooling metals rapidly by immersing them in liquids
or gases.
R
R
Chart- Pronounced
R-bar chart. See also range chart.
RMS- RMS is
the abbreviation for root mean square. The
RMS is the average of the squares of the deviations
of the high and low values. Compare with AA.
Random Errors-
Random errors result from erratic malfunctions
of any part of the measurement system including the
observer. For example, a loose element that may unpredictably
change positions could add errors. Random errors are
often found by the discrepancies when a measurement
act is repeated. Random errors are also known as accidental
errors. See also errors, systematic errors and illegitimate
errors.
Random Number
Table- A random number table is a table
of numbers in which there is no discernable pattern
of occurrences.
Random Sample-
A random sample is the selection of a sample
without bias. See also sampling.
Range Chart- A
range chart is that portion of a worksheet
(q.v.) showing the range of the samples.
Ray- A ray
of light is an imaginary line perpendicular to a wave
front (q.v.). See also light rays.
Ray Tracing- Ray
tracing is the study of optical systems by means
of rays.
Readability- Readability
is the relative ease with which the measurement
can be distinguished. For example, both a plain micrometer
and a vernier caliper have the same discrimination,
but the plain micrometer is more readable.
Real Image- A
real image is the image formed by light rays
from an object passing through a convergent (convex)
lens. The real image lies on the side of the lens
away from the object and is inverted. See also virtual
image.
Ream- A machine
operation consisting of enlarging a hole slightly
to a close tolerance.
Reciprocation-
A straight-line, back-and-forth motion or oscillation.
Reference Dimension-
A dimension used only for information. It does
not govern production or inspection.
Reference Plane-
The reference plane is the plane in which
the reference points lie. It is always perpendicular
to the line of reference. The reference plane by definition
must be flat. The reference plane is also known as
the datum plane. See also flatness and surface plate.
Reference Point-
The reference point is the position on
a part feature from which a dimension is expressed.
Usually, but not necessarily, it is expressed as zero.
See also measured point.
Reflection- Reflection
is the change of direction of light when it is
directed upon a suitable surface.
Refraction- Refraction
is the change in path when light passes from one
transparent medium into a different medium.
Regardless of
Feature Size (RFS)- The condition in which tolerances
of position or form must be met irrespective of where
the feature lies within its size tolerance.
Reliability- The
reliability is the probability of achieving
desired results. Reliability is a relative matter
whereas accuracy is comparative and precision is positive.
Relief- A
slight variance in the dimension of a machine part
to allow for clearance.
Repeatability-
Repeatability is the variation among several
measurements taken with one instrument on one part
feature. It is a test of precision, not of accuracy.
Resolution- Resolution
is the ability to visually distinguish with the
unaided eye between separate items, usually lines.
It is the ratio of the width of one scale division
(one output unit) to the width of the hand (the read-out
element). Resolution is not the same as readability.
Resolving Power-
The resolving power is the property by
which small elements are distinctly separated., For
practical work this is more important than the magnification.
The measure of resolving power is numerical aperture
(q.v.).
Reversal Technique-
The reversal technique or reversal process
is method for detecting or canceling small changes
by comparing a variable with itself but with reversed
algebraic sign.
Right Hand Rule-
A method to define positive and negative vector
directions in space.
Rivet- A metal
pin with a head, used to secure two or more pieces.
Rotate- To
turn an alignment system about one or more of its
axes.
Roughness Average-
The roughness average is the arithmetic
average (AA) of the absolute values of the profile
height deviations. It is sometimes referred to by
its earlier term, centerline average (CLA).
This is the method standardized for use in the U.S.
Many other methods are also used and some ten have
been standar | 
