Unit 15 Geometric Dimensioning and Tolerancing Objectives Describe

Unit 15 Geometric Dimensioning and Tolerancing

Objectives • Describe the purposes of geometric dimensioning and tolerancing (GD&T). • Define various applications of geometric tolerances. • Identify various GD&T symbols. • Define various terms relating to GD&T. • Identify datum surfaces. • Interpret the meaning of material condition modifiers on a print. • Interpret the meaning of GD&T symbols on a print. Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Geometric Dimensioning and Tolerancing • • • Defines amount of variation permitted Reduces drawing changes Increases productivity Avoids scrapping functional parts Clarifies critical part features Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

GD&T Application • Form tolerances—control form or shape • Orientation tolerances—control orientation of features to one another • Location tolerances—control variance from true position • Profile tolerances—control tolerance maintained from true profile • Runout tolerances—control relationship between features and axis Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

GD&T Symbols Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

GD&T Symbols (cont. ) Datum feature symbol Feature control frame Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

GD&T Terminology • Datum—exact plane, point, line, or axis • Basic dimension—theoretical exact value for feature or datum • Feature—actual portion of a part • Size feature—feature with center plane or axis • True position—theoretical exact location of center plane or axis of a size feature Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Datums • Controlled by geometric characteristic symbols • Datum plane— theoretically exact reference base • Datum features— actual surfaces used to establish datums Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Datums (cont. ) • Datum targets—specific points requiring machining • Datum target symbol Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Material Condition Modifiers • Indicate bonus tolerance – Maximum material condition (MMC) – Least material condition (LMC) – Regardless of feature size (RFS) Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Maximum Material Condition • Internal features at low limit size • External features at high limit size Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Least Material Condition • Internal features at high limit size • External features at low limit size Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Regardless of Feature Size • Tolerance zone limited to specific value • No change regardless of actual feature size • Symbol no longer used Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Form Tolerances • Circularity (roundness)—variation allowed between max and min radii in single cross section Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Form Tolerances (cont. ) • Cylindericity—tolerance zone between two concentric cylinders Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Form Tolerances (cont. ) • Straightness—all points in a straight line Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Form Tolerances (cont. ) • Flatness—all points on one plane Fig 15 -23 Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Orientation Tolerances • Angularity—surface or axis at specified angle (other than 90 ) to datum Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Orientation Tolerances (cont. ) • Perpendicularity—surface or axis at right angle (90 ) to datum plane or axis Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Orientation Tolerances (cont. ) • Parallelism—surface or axis the same distance at all points from datum plane or axis Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Location Tolerances • Position—tolerance zone within which an axis or center plane is allowed to vary from true position Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Location Tolerances (cont. ) • Concentricity—equal midpoint distance of all elements on each side of datum axis, RFS Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Location Tolerances (cont. ) • Symmetry—controlled elements equidistant about center plane Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Profile Tolerances • Profile of a line—all points on a line within specified tolerance zone of true profile Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Profile Tolerances (cont. ) • Profile of a surface—all points on a surface within specified tolerance zone of true profile Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Runout Tolerances • Circular runout—controls circular elements independently as part is rotated 360 Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Runout Tolerances (cont. ) • Total runout—controls all circular elements simultaneously as part is rotated 360 Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.