19076987 winncad gdt definitions

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Paul Corona

www.winncad.com

GD&T Symbols, Terms and Definitions ASME Y14.5M-1994

(Dimensioning and Tolerancing)
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COMMON TERMS AND DEFINITIONS

Basic DimensionA numerical value used to describe the theoretically exact size, profile, orientation, or

location of a feature or datum target. It is the basis from which permissible variations areestablished by tolerances on other dimensions, in notes, or in feature control frames.

DatumA theoretically exact point, axis, or plane derived from the true geometric counterpart of

a specified datum feature. A datum is the origin from which the location or geometric

characteristics of features of a part are established.

Datum TargetA specific line, or area on a part used to establish a datum.

Maximum Material Condition (MMC)The condition in which a feature of size contains the maximum amount of material withinthe stated limits of size-for example, minimum hole diameter, maximum shaft diameter.

Least Material Condition (LMC)The condition in which a feature of size contains the least amount of material within the

stated limits of size-for example, maximum hole diameter, minimum shaft diameter.

Regardless of Feature Size (RFS):The term used to indicate that a geometric tolerance or datum reference applies at any

increment of size of the feature within its size tolerance.


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Full Indicator MovementThe total movement of an indicator when appropriately applied to a surface to measure

its variations (formerly called total indicator reading-TIR).

Virtual Condition

The boundary generated by the collective effects of the specified MMC limit of size of afeature and any applicable geometric tolerances.

Feature Control FrameThe feature control frame consists of: A) type of control (geometric characteristic), B)

tolerance zone, C) tolerance zone modifiers (i.e., MMC or RFS), D) datum references ifapplicable and any datum reference modifiers.

PROFILE TOLERANCES

Profile of a LineA uniform two dimensional zone limited by two parallel zone lines extending along the

length of a feature.

Profile of a SurfaceA uniform three dimensional zone contained between two envelope surfaces separated

by the tolerance zone across the entire length of a surface.

ORIENTATION TOLERANCES

AngularityThe distance between two parallel planes, inclined at a specified basic angle in which

the surface, axis, or center plane of the feature must lie.


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Perpendicularity (squareness)The condition of a surface, axis, median plane, or line which is exactly at 90 degrees

with respect to a datum plane or axis.

ParallelismThe condition of a surface or axis which is equidistant at all points from a datum of

reference.

LOCATIONAL TOLERANCES

True PositionA zone within which the center, axis, or center plane of a feature of size is permitted to

vary from its true (theoretically exact) position.

ConcentricityA cylindrical tolerance zone whose axis coincides with the datum axis and within whichall cross-sectional axes of the feature being controlled must lie. (Note: Concentricity is

very expensive and time-consuming to measure. Recommended that you try position orrunout as an alternative tolerance.)

RUNOUT TOLERANCES

RunoutA composite tolerance used to control the relationship of one or more features of a part

to a datum axis during a full 360 degree rotation about the datum axis.


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Circular RunoutEach circular element of the feature/part must be within the runout tolerance.

Total RunoutAll surface elements across the entire surface of the part must be within the runout

tolerance.

FORM TOLERANCES

FlatnessA two dimensional tolerance zone defined by two parallel planes within which the entire

surface must lie.

StraightnessA condition where an element of a surface or an axis is a straight line.

CircularityA condition on a surface of revolution (cylinder, cone, sphere) where all points of thesurface intersected by any plane perpendicular to a common axis (cylinder, cone) or

passing through a common center (sphere) are equidistant from the axis of the center.

CylindricityA condition on a surface of revolution in which all points of the surface are equidistant

from a common axis.

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19076987 winncad gdt definitions

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