Geometrical tolerance

help to understand basic of geometrical tolerances

1. GEOMETRICAL TOLERANCES PREPARED BY:-CHETAN HIWASE ROLL NO:-173510 10/18/2017 1

2. GEOMETRICAL TOLERARANCES Geometrical tolerances is a system for defined and communicating engineering tolerances . It uses a symbolic language on engineering drawings and computer-generated three-dimensional solid models that explicitly describes nominal tolerances and its allowable variation.  It tells the manufacturing staff and machines what degree of accuracy and precision  is needed on each controlled feature of the part.  Geometrical tolerances can add quality and reduce cost at the same time through producibility. Geometric tolerance reading helps to understand to specify and control the form, location and orientation of the features of components and manufactured parts. 10/18/2017 2

3. HISTORY The origin of Geometrical tolerances has been credited to a man named Stanley Parker, who developed the concept of "true position" in 1938. ]  While very little is known about the life of Stanley Parker, it is recorded that he worked at the Royal Torpedo Factory in Alexandria, Scotland. Parker's work was used to increase production of naval weapons . 10/18/2017 3

4. REPRESENTATION OF GEOMETRIC TOLERANCES 10/18/2017 4

5. DATUM PLANES Primary datum plane :  The primary datum is selected to provide functional relationships , standardizations and repeatability between surfaces. A standardization of size is desired in the manufacturing of a part. Consideration of how parts are orientated to each other is very important. The chosen primary datum must insure precise measurements. Secondary Datum Plane : Secondary datums are produced perpendicular to the primary datum so measurements can be referenced from them. Tertiary Datum Plane : Tertiary datum is always perpendicular to both the primary and secondary datums ensuring a fixed position from three related parts. 10/18/2017 5

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7. Geometric Tolerancing Modifiers There are three directly implied modifiers 1)Regardless of Feature Size (RFS ) 2)Maximum Material Condition (MMC) 3) Least Material Condition (LMC) Regardless of Feature Size (RFS):  RFS is the default modifier. so if there is no modifier symbol shown in feature control frame. RFS is used when the size feature does not affect the specified tolerance.   Maximum Material Condition (MMC ): MMC can be used to constrain the tolerance on given dimensions. MMC can be defined as the condition of a part feature where the maximum amount of material is required. MMC is also used to maintain clearance and fit between shafts and holes. With MMC, The given tolerance will be applied as Maximum shaft diameter and Minimum hole diameter . Least Material Condition (LMC ):   LMC can be defined as the condition of a part feature where minimum amount of material is required. With LMC, The given tolerance will be applied as Minimum shaft diameter and Maximum hole diameter . 10/18/2017 7

8. TOLERANCE OF ORIENTATION 10/18/2017 8

9. 1.Perpendicularity The normal form or Surface Perpendicularity is a tolerance that controls Perpendicularity between two 90°  surfaces. Axis Perpendicularity is a tolerance that controls how perpendicular a specific axis needs to be to a datum. 10/18/2017 9

10. 2.Parallelism The normal form or Surface Parallelism is a tolerance that controls parallelism between two surfaces or features. The surface form is controlled similar to flatness with two parallel planes acting as its tolerance zone. Axis Parallelism is a tolerance that controls how parallel a specific parts central axis needs to be to a datum plane or axis. 10/18/2017 10

11. ANGULARITY Angularity is the symbol that describes the specific orientation of one feature to another at a referenced angle.  The tolerance does not directly control the angle variation and should not be confused with an angular dimension tolerance such as ± 5°.  In fact the angle for now becomes a Basic Dimension, since it is controlled by your geometric tolerance . 10/18/2017 11

12. TOLERANCE OF FORM 10/18/2017 12

13. Straightness Straightness actually has two very different functions in GD&T depending how it is called out. In its normal form or Surface Straightness, is a tolerance that controls the form of a line somewhere on the surface or the feature. Axis Straightness is a tolerance that controls how much curve is allowed in the part’s axis .  10/18/2017 13

14. FLATNESS It is a common symbol that references how flat a surface is regardless of any other datum. Flatness is can be measured using a height gauge run across the surface of the part if only the reference feature is held parallel. Modern CMM’s are best for measuring the part as they can create virtual planes that the true surface profile can be compared to. 10/18/2017 14

15. Circularity  Circularity tolerance is used to control the roundness of circular parts or features.  Circularity is measured by constraining a part, rotating it around the central axis while a height gauge records the variation of the surface. The height gauge must have total variation less than the tolerance amount. 10/18/2017 15

16. CYLINDRICITY The Cylindricity symbol is used to describe how close an object conforms to a true cylinder. Cylindricity is measured by constraining a part on its axis, and rotating it around while a height gauge records the variation of the surface in several locations along the length. Commonly used for shaft, pins and critical cylindrical parts. 10/18/2017 16

17. TOLERANCE OF LOCATION 10/18/2017 17

18. SYMMETRY Symmetry Tolerance controls the median points of a feature of size, symmetry tolerance is applied to non circular features. Symmetry Tolerance is a three-dimensional geometric tolerance that controls how much the median points between two features may deviate from a specified center plane or axis.  10/18/2017 18

19. CONCENTRICITY Concentricity, sometimes called coaxially, is a tolerance that controls the central axis of the referenced feature. its difficulty in establishing the mid points of the feature. EXAMPLE:-Transmission gears 10/18/2017 19

20. POSITION   The True Position is the exact coordinate Position is probably the most widely used symbol in GD&T. Position in terms of the axis, point or plane defines how much variation a feature can have from a specified exact true location.  10/18/2017 20

21. RUNOUT In GD&T, total runout  is a complex tolerance that controls feature s  straightness , profile, angularity , and other geometric variation. Circular Runout zone is limited in the measuring plane perpendicular to the axis by two concentric circles, the common centre of which lies on the datum axis 10/18/2017 21

22. CIRCULAR RUNOUT 10/18/2017 22

23. TOTAL RUNOUT 10/18/2017 23

24. PROFILE TOLERANCES 10/18/2017 24

25. LINE PROFILE 10/18/2017 25

26. SURFACE PROFILE 10/18/2017 26

27. REFERANCES Geometrical dimensioning and tolerances by james d. Meadoes Geometrical dimensioning and tolerances for design, manufacturing and inspection by g.henzold . Geometrical dimensioning and tolerances paul green 10/18/2017 27

28. THANK YOU 10/18/2017 28