Inspecting a Prismatic Part 321

actual local size

An unrelated size dimension that indicates the measurement of an imaginary plane that intersects a feature. The actual local size, also called the cross-sectional dimension, is often measured with calipers or a micrometer.

actual mating envelope

AME. A geometrically perfect shape that is a 'best fit' around a feature. The actual mating envelope is the smallest possible cylinder contacting a shaft at its highest points or the largest possible cylinder contacting a hole at its highest points.

angularity

A three-dimensional orientation tolerance that describes the allowable variability in the angular relationship between a surface and a datum. Angularity is a related tolerance.

axis

A theoretical straight line that lies in the center of an object. The axis of a feature helps determine the cross-sectional dimension.

CAD

Computer-aided design. A computer software program that aids in the automated design and technical precision drawing of a part, product, process, or building. A CAD model can be used like a part drawing.

calipers

A measuring instrument with a pair of jaws on one end and a long beam containing a marked scale of unit divisions. Caliper jaws can measure both internal and external features.

callouts

Information on a print that refers to a specific part feature rather than the whole part. Callouts, or local notes, communicate specifications such as chamfer angle and hole diameter.

center plane

A theoretical plane used as a datum reference at the center of a feature of size. Center planes help allow for the measurement of cross-sectional dimensions.

CMM

Coordinate measuring machine. A sophisticated measuring instrument that uses a suspended probe to measure parts in three-dimensional space. CMMs operate using either contact or noncontact methods.

CMM arms

A portable measuring device consisting of segments connected by joints. CMM arms operate using either contact or noncontact methods.

contour

A curved part of a workpiece. Contour features are complex and generally calculated using CAD/CAM software.

coordinate measuring machines

CMMs. A sophisticated measuring instrument that uses a suspended probe to measure parts in three-dimensional space. Coordinate measuring machines operate using either contact or noncontact methods.

cross-sectional dimension

An unrelated size dimension that indicates the measurement of an imaginary plane that intersects a feature. The cross-sectional dimension, also called the actual local size, is often measured with calipers or a micrometer.

datums

A point of reference for machine tools, programs, and fixtures from which measurements are taken. A datum can be a hole, a line, or any three-dimensional shape.

dial indicators

A measuring instrument with a contact point attached to a spindle and gears that move a pointer on the dial. Dial indicators have graduations that show different measurement values.

feature control frame

A series of compartments on a print containing symbols and values that describe the geometric tolerance of a feature. The feature control frame’s order and purpose follow a consistent standard.

flatness

A three-dimensional form tolerance that describes the allowable variability in the shape and appearance of a surface that lies in a plane. Flatness is a type of form tolerance.

form tolerances

A geometric tolerance that limits the amount of acceptable variation in the shape of a feature. Form tolerances include straightness, flatness, circularity, and cylindricity.

functional gages

A gage representing a worst-case mating part that provides a simple pass/fail assessment of the inspected part. Functional gages often can quickly inspect several features at once.

GD&T

Geometric dimensioning and tolerancing. An international standard for communicating instructions about the design and manufacturing of parts. GD&T uses universal symbols and emphasizes the function of the part.

geometric dimensioning and tolerancing

GD&T. An international standard for communicating instructions about the design and manufacturing of parts. Geometric Dimensioning and Tolerancing uses universal symbols and emphasizes the function of the part.

go/no-go gage

An instrument with an established standard size that determines whether a part feature passes or fails inspection. Go/no-go gages do not determine the degree of variation.

height gage

A measuring device with a unit and extending arm that slide up and down a vertical column that is mounted on a base such as a granite surface plate, and a unit with an extending arm that slides up and down along a main scale beam. Height gages may use a standard scale beam, a vernier scale, a dial indicator, or a digital display to measure vertical dimensions and other distances.

hypotenuse

The longest side of a right triangle, which is located opposite the right angle. To find the measurement of a hypotenuse, use the Pythagorean theorem (A² + B² = C²) and solve for C.

inspection

The examination of a product during or after its creation to confirm that it adheres to specifications. Inspection allows manufacturers to identify and correct product defects.

legs

A side of a right triangle other than the hypotenuse. The legs of the right triangle are represented by the letters a and b in the Pythagorean theorem.

location tolerances

A geometric tolerance that limits the location or placement of features relative to a datum or other features. Location tolerances include position, concentricity, and symmetry.

material condition modifiers

Defines the tolerance of a feature in relation to its acceptable size limits. The three material condition modifiers in GD&T are maximum material condition, least material condition, and regardless of feature size.

maximum material condition

MMC. The point at which a feature contains the greatest amount of material within its acceptable size limit. Examples of maximum material condition include the smallest acceptable hole and the largest acceptable shaft.

micrometer

A U-shaped measuring instrument with a threaded spindle that slowly advances toward a small anvil. Micrometers are available in numerous types for measuring assorted dimensions and features.

nominal size

The ideal measurement of a part or part feature that is specified in the part print. Nominal sizes are geometrically perfect and are used to establish tolerance values.

optical comparators

A sophisticated measuring instrument that projects an image of a part onto a screen so that the shape, size, and location of its features can be compared to measurement markings. Optical comparators can be used to inspect both surface and profile features in two dimensions.

orientation tolerances

A geometric tolerance that limits the direction, or orientation, of a feature in relation to other features. Orientation tolerances are related tolerances.

orientation tolerances

A geometric tolerance that limits the direction, or orientation, of a feature in relation to other features. Orientation tolerances include angularity, perpendicularity, and parallelism.

parallelism

A three-dimensional orientation tolerance that describes the equal distance between pairs of points, lines, or planes. Parallelism is a related tolerance.

perpendicularity

A three-dimensional orientation tolerance that describes the allowable variability in the 90° angular relationship between a surface and a datum. Perpendicularity is a related tolerance.

plane

A flat surface that extends infinitely in any direction in three dimensions. A plane is represented on blueprints by a square or rectangle.

position

A three-dimensional location tolerance that controls how much the location of a feature can deviate from its true position. Position is a related tolerance.

precision square

An L-shaped tool that forms a 90° angle. Precision squares are used to inspect the perpendicularity of one surface in relation to another.

prismatic part

A solid geometric figure with two end faces that are parallel polygons whose corners are connected by perpendicular lines. Prismatic parts are inspected according to feature characteristics and associated tolerances.

profile of a line

A two-dimensional profile tolerance that describes the allowable variability in the contour of the edge seen in the section view. Profile of a line can be either an individual or a related tolerance.

profile of a surface

A three-dimensional profile tolerance that describes the allowable variability in the contour of a surface. Profile of a surface can be either an individual or a related tolerance.

profile tolerances

A geometric tolerance that controls the size, location, orientation, and form of a feature. Profile tolerances can be either individual or related.

Pythagorean theorem

A mathematical rule that describes how the sides of a right triangle are related. The Pythagorean theorem states that the sum of the square of both sides is equal to the square of the hypotenuse (A² + B = C).

regardless of feature size

RFS. A modifier indicating that the stated tolerance for a feature applies regardless of its actual size within an acceptable size limit. If the location is controlled regardless of feature size, it should be inspected with a variable measuring device.

related actual mating envelope

Related AME. A geometrically perfect shape that is a 'best fit' around a feature. A related actual mating envelope is related to other part features and constrained by applicable datums.

right triangle

A triangle containing exactly one 90° angle. Right triangles include two other angles that must total 90 degrees.

runout tolerances

A geometric tolerance that simultaneously limits the form, location, and orientation of cylindrical parts. Runout tolerances are related tolerances requiring a datum axis.

sensitivity

The smallest change in a measurement that an instrument is capable of detecting. Instruments with greater sensitivity provide more exact readings.

sine bar

A steel bar with matching cylinders at each end used to position parts at various angles. A sine bar is used to inspect angularity.

size dimensions

A linear measurement across two opposing points, lines, planes, or surfaces. A size dimension is a required characteristic of a feature of size.

square

A common power in which a number is multiplied by itself once. A square can be expressed by stating the value and then 'to the second power' or as the value with the superscript 2 beside it.

square root

A mathematical function that shows which unknown number is multiplied by itself one time. The square root of 49 is seven.

straightness

A two-dimensional form tolerance that describes the allowable variability in the shape and appearance of a line in a section view. Straightness is an individual tolerance.

surface plate

A hard, flat surface, usually made of granite, that is used as a base for mounting gages. A height gage must be mounted on a surface plate.

tolerances

The amount of permitted variation from a specified dimension of a part. A part within tolerances will meet specifications and pass inspection.

total indicator reading

TIR. The absolute value of the total deviation of a dial indicator's movement. Total indicator reading is calculated to inspect the flatness of a prismatic part.

true position

The imaginary perfect position of a feature of size as defined by coordinates and dimensions of a part drawing. True position serves as the reference location from which a feature may deviate with a position tolerance.

true profile

The perfect, imaginary profile of a feature as described by the design specifications. The profile tolerances compare the actual profile of a feature to the true profile.

unrelated actual mating envelope

Unrelated AME. A geometrically perfect shape that is a 'best fit' around a feature. An unrelated actual mating envelope is not constrained by other part features or datums.

virtual condition

VC. A constant worst case imaginary boundary used when parts are toleranced for assembly that is defined by the collective effects of a feature's size and geometric tolerance. For an external feature, the VC is the outer boundary, and for an internal feature, the VC is the inner boundary.