14 symbols of gd&t

This PPT discuss the 14 geometric symbols used in GD&T classified under five controls. Only important points are mentioned. Kindly mention, if any other important points are missed out. The sources of the content (including pics) are from various sites which details GD&T. The PPT with modifiers and additional symbols (in detail) will be updated soon.

1. Symbols of GD&T (in detail) SREELAKSHMY V.U (B.E)

2. There are 14 geometrical characteristics symbol which controls the features in GD&T. T hey are classified under five controls and are given: FORM Straightness Flatness Circularity Cylindricity ORIENTATION Angularity Perpendicularity Parallelism LOCATION Position Concentricity Symmetry PROFILE Profile of a line Profile of a surface RUN OUT Circular Run out Total Run out

3. Straightness In this feature, all elements are proposed to be in the straight line Straightness error is the distance between two parallel lines which include all elements of a line Straightness control is a geometric tolerance that when directed to a surface that limit the amount of straightness error Straightness control requires no datum reference and modifiers (MMC,LMC, P, T) It controls each line independently and separately If tolerance zone for straightness is applied to a FOS is a cylinder, diameter modifier is used If modifier is given in the frame, then the condition is used to describe the axis of FOS

4. Flatness In this feature, all elements are supposed to be in one plane Flatness error is the distance between two parallel planes which include all elements of a surface (High and low points) Flatness control is a geometric tolerance that limits the amount of flatness error Flatness feature requires no datum and no modifiers. And it must be applied to a planar surface The distance between the parallel plane is determined by the flatness control tolerance value

5. Circularity It is a condition where all points of a surface of revolution at any section perpendicular to an axis are equidistant from the axis Circularity error is the radial distance between two co-axial diameters which include all elements of a circular feature Circularity control limits the amount of circularity error Circularity feature requires no datum reference, modifiers (M,L,P,T) It controls each circular element independently Tolerance zone for a circularity control applies to a diameter in two co-axial circles Circularity control do not over ride Rule #1

6. Cylindricity It is the condition of a surface of revolution in which all points of the surface are equidistant from a common axis Cylindricity error is the radial distance between two co-axial cylinders which includes all elements of a cylindrical surface. Cylindricity control limits amount of cylindricity error Cylindricity feature requires no datum reference and modifiers Cylindricity feature controls the form of diameter of a perfect cylinder

7. Angularity It is used to control the angle of the surface Angularity requires datum reference and an angle must be specified between the tolerance feature and datum reference When angularity is applied to a plane , the tolerance zone will be two parallel planes oriented by a basic angle and all the elements will lie within the tolerance zone When angularity is applied to FOS , it controls the orientation of the axis of FOS When diameter is specified before the angular tolerance value, it indicates that the tolerance zone is cylindrical

8. Perpendicularity When the perpendicularity is applied to a surface , the tolerance zone is two parallel planes which are 90 degree to the datum When the perpendicularity is applied to a planar FOS , its tolerance zone is applied to both the surface of FOS When the perpendicularity control is applied to a planar surface , it controls the orientation of flatness of the surface When the perpendicularity control is applied to a FOS , it control the orientation of axis of the FOS If MMC is indicated with perpendicularity control, then bonus tolerance is permissible When the diameter is specified before the tolerance value, then the shape of the tolerance zone is cylindrical

9. Parallelism When parallelism is applied to a planar surface, the tolerance zone is two parallel planes which are parallel to the datum plane. When parallelism is applied to a FOS, its tolerance zone is applied to the axis or center plane of the FOS. When the diameter is specified before the tolerance value, then the shape of the tolerance zone is cylindrical When the parallelism control contains a diameter symbol in front of the tolerance value, the shape of tolerance value will be cylindrical The axis of the tolerance diameter must be within the tolerance zone the tolerance zone may float within the allowable location tolerance zone

10. Position Tolerance of position (TOP) It is used to control the location of the FOS or a pattern of FOS True position is the theoretically exact location of a FOS TOP control is a geometric tolerance that defines the location tolerance of FOS from its true position. Modifiers and datum references are used when TOP is used When Modifier is given for a part with TOP, then the tolerance is applied only to that modifier condition When TOP is applied on MMC, bonus tolerance and datum shift is permitted

11. Concentricity It is the condition where the mid points of all diametrically opposed elements of a surface of revolution are congruent with the axis of a datum feature. All the median points of the tolerance diameter must be within the tolerance zone. A concentricity control, datum references are always applied at RFS Concentricity requires datum reference and must be applied to a cylindrical FOS and at RFS The tolerance zone for a concentricity control is a cylinder that is co axial with the datum

12. Symmetry It is the condition where the median points of all opposed elements of two or more feature surfaces are congruent with the datum axis or datum center plane of a datum feature The symmetry control requires datum reference and it must be applied to a planar FOS and RFS The symmetry tolerance value determines the size of tolerance zone The tolerance zone for a symmetry control is two parallel planes centered about the datum center plane The distance between the plane is equal to the symmetry control tolerance value Median points of tolerance feature must be within the tolerance zone

13. Profile of a line Profile of a line establishes a two-dimensional tolerance zone that controls individual line elements of a  feature or surface.  Profile of a line is usually applied to parts with varying cross-sections, or to specific cross sections critical to a part's function.  Profile control is a geometric tolerance which specifies a uniform boundary along the true profile that elements of a surface must lie within When a profile of a line control is specified the tolerance zone is two uniform lines. The tolerance zone applies for each line element of the surface It has 2D tolerance zone It can be used with the datum feature as a related feature control and without a datum reference as a form control

14. Profile of a surface It is a powerful geometric tolerance which is used to control the part surface It controls the size, location, orientation and form When the profile of a surface control is specified, tolerance zone is uniform boundary. The boundary applies for the full length and width of the surface It must have a datum reference and should be applied to a true profile It has 3D tolerance zone and it can be used to tolerance a polygon, conical feature

15. Circular Run out It is a composite control that affects the form, orientation, location of circular elements of a part feature relative to a datum axis It is applied to each circular element of the tolerance feature independently Tolerance zone exist for each circular element of the tolerance diameter The shape of the tolerance zone is two co-axial circles whose centers are located on the datum axis. It is known as composite control because it limits the circularity, orientation and axis offset of a diameter. Circular run out tolerance zone is the radial distance between circles equal to the run out tolerance value

16. Total Run out It is a composite control that affects the form, orientation, location of all surface elements of a diameter relative to a datum axis Total run out requires a datum reference and it must be applied at RFS The run out tolerance value is equal to the radial distance between the two cylinders The tolerance zone of a total run out is the two co-axial cylinders whose centers are located on the datum axis It is also a composite control as it limits the location, orientation and cylindricity

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