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Geometric Dimensioning and Tolerancing

Geometric Dimensioning and Tolerancing. Chapter 3, Datums. Introduction. Datums are nothing more and nothing less than the physical features of parts from which to make repeatable measurements . These features are considered theoretically exact .

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Geometric Dimensioning and Tolerancing

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  1. Geometric Dimensioning and Tolerancing Chapter 3, Datums

  2. Introduction • Datums are nothing more and nothing less than the physical features of parts from which to make repeatable measurements. • These features are considered theoretically exact. • Datumsdefine a coordinate system from which to measure everything. • Datums are usually a plane, a line, or a point. • We will need to label the datums on our drawing so that the part inspector will know from where to measure.

  3. Datum Feature Symbol • Datum Feature Symbol

  4. Three-Plane Concept • define primary, secondary, and tertiary datum planes • the primary datum is the one that functionally is usually the most critical feature or surface of the part • the primary datum feature of the part will make contact with the theoretical datum plane in a minimum of three points

  5. Three-Plane Concept • define primary, secondary, and tertiary datum planes • the secondary datum plane is  to the primary datum • secondary datum feature is the one that functionally is the 2nd most critical feature or surface of the part • 2 point minimum contact

  6. Three-Plane Concept • define primary, secondary, and tertiary datum planes • the tertiary datum plane is  to the primary & sec. datums • 1 point minimum contact

  7. Three-Plane Concept - Circular • circular parts also require a three-plane concept for repeatable orientation • the primary datum is usually one flat surface of the part, • defines a datum axis along the center of cylinder should be a construction line (or omitted) should have a center line

  8. Three-Plane Concept - Circular • datum A defines an axis along the center of the cylinder

  9. Partial Datums • Occasionally, designs require a datum on a particular surface, but not necessarily the entire surface.

  10. Features with and without Size 1.9

  11. Establishing Datums from Primary Plane Surfaces 5 H 7 ( 5 / 5 . 0 1 2 ) 1 5 . 9 ± 0 . 2 0 . 2 2 5 ± 0 . 3 L L M - 1 0 x 1 . 2 5 1 2 . 7 ± 0 . 1 2 5 ± 0 . 3 H 2 X 6 ± 0 . 2 5 T h e o r y D a t u m f e a t u r e s H a n d L a r e m a t e d w i t h a t h e o r e t i c a l p e r f e c t p l a n e c o n t a c t i n g t h e h i g h p o i n t s o f t h e d a t u m f e a t u r e . P h y s i c a l Datum features H and L are mated on the high points of the manufacturing or inspection equipment 6.15 D a t u m D a t u m W o r k p i e c e f e a t u r e f e a t u r e W O R K P I E C E S U R F A C E D a t u m T E f e a t u r e s i m u l a t o r T o o l & g a g e P h y s i c a l d a t u m f e a t u r e s i m u l a t o r v a r i a t i o n S i m u l a t e d ( s u r f a c e p l a t e o r T h e o r e t i c a l d a t u m p l a n e p r o c e s s i n g e q u i p m e n t ) d a t u m P l a n e M a g n i f i e d V i e w

  12. Establishing Datums from Primary Plane Surfaces P h y s i c a l Datum feature D a t u m W o r k p i e c e f e a t u r e W O R K P I E C E Datum feature simulator S U R F A C E Tool and gage variation P h y s i c a l d a t u m f e a t u r e s i m u l a t o r ( s u r f a c e p l a t e o r Simulated datum plane p r o c e s s i n g e q u i p m e n t ) Theoretical datum plane Magnified View 6.15

  13. D a t u m f e a t u r e H e s t a b - D a t u m f e a t u r e N e s t a b - l i s h e s a p l a n e o n t h e h i g h l i s h e s a p l a n e o n t h e h i g h p o i n t s o f t h e b o t t o m p o i n t s o f t h e l e f t s u r f a c e . s u r f a c e . D a t u m f e a t u r e L e s t a b - l i s h e s a p l a n e o n t h e h i g h p o i n t s o f t h e r e a r s u r f a c e . D a t u m f e a t u r e M e s t a b - l i s h e s a p l a n e o n t h e h i g h p o i n t s o f t h e l e f t s i d e o f t h e s l o t . D a t u m f e a t u r e K e s t a b l i s h e s a p l a n e o n t h e h i g h p o i n t s o f t w o s u r f a c e s . Datum Features without Size P L 5 H 7 ( 5 / 5 . 0 1 2 ) 1 5 . 9 ± 0 . 2 0 . 2 2 5 ± 0 . 3 M - 1 0 x 1 . 2 5 N M 2 S U R F A C E S K 1 2 . 7 ± 0 . 1 H 2 5 ± 0 . 3 2 X 6 ± 0 . 2 5 S 1 7 ± 0 . 0 2 D a t u m p l a n e s e s t a b l i s h e d f r o m p l a n a r d a t u m f e a t u r e s 6.16

  14. D a t u m f e a t u r e H e s t a b - D a t u m f e a t u r e N e s t a b - l i s h e s a p l a n e o n t h e h i g h l i s h e s a p l a n e o n t h e h i g h p o i n t s o f t h e b o t t o m p o i n t s o f t h e l e f t s u r f a c e . s u r f a c e . D a t u m f e a t u r e L e s t a b - l i s h e s a p l a n e o n t h e h i g h p o i n t s o f t h e r e a r s u r f a c e . D a t u m f e a t u r e M e s t a b - l i s h e s a p l a n e o n t h e h i g h p o i n t s o f t h e l e f t s i d e o f t h e s l o t . D a t u m f e a t u r e K e s t a b l i s h e s a p l a n e o n t h e h i g h p o i n t s o f t w o s u r f a c e s . Datum Features without Size P L 5 H 7 ( 5 / 5 . 0 1 2 ) 1 5 . 9 ± 0 . 2 0 . 2 2 5 ± 0 . 3 M - 1 0 x 1 . 2 5 N M 2 S U R F A C E S K 1 2 . 7 ± 0 . 1 H 2 5 ± 0 . 3 2 X 6 ± 0 . 2 5 S 1 7 ± 0 . 0 2 D a t u m p l a n e s e s t a b l i s h e d f r o m p l a n a r d a t u m f e a t u r e s 6.16

  15. D a t u m f e a t u r e H e s t a b - D a t u m f e a t u r e N e s t a b - l i s h e s a p l a n e o n t h e h i g h l i s h e s a p l a n e o n t h e h i g h p o i n t s o f t h e b o t t o m p o i n t s o f t h e l e f t s u r f a c e . s u r f a c e . D a t u m f e a t u r e L e s t a b - l i s h e s a p l a n e o n t h e h i g h p o i n t s o f t h e r e a r s u r f a c e . D a t u m f e a t u r e M e s t a b - l i s h e s a p l a n e o n t h e h i g h p o i n t s o f t h e l e f t s i d e o f t h e s l o t . D a t u m f e a t u r e K e s t a b l i s h e s a p l a n e o n t h e h i g h p o i n t s o f t w o s u r f a c e s . Datum Features without Size P L 5 H 7 ( 5 / 5 . 0 1 2 ) 1 5 . 9 ± 0 . 2 0 . 2 2 5 ± 0 . 3 M - 1 0 x 1 . 2 5 N M 2 S U R F A C E S K 1 2 . 7 ± 0 . 1 H 2 5 ± 0 . 3 2 X 6 ± 0 . 2 5 S 1 7 ± 0 . 0 2 D a t u m p l a n e s e s t a b l i s h e d f r o m p l a n a r d a t u m f e a t u r e s 6.16

  16. D a t u m f e a t u r e H e s t a b - D a t u m f e a t u r e N e s t a b - l i s h e s a p l a n e o n t h e h i g h l i s h e s a p l a n e o n t h e h i g h p o i n t s o f t h e b o t t o m p o i n t s o f t h e l e f t s u r f a c e . s u r f a c e . D a t u m f e a t u r e L e s t a b - l i s h e s a p l a n e o n t h e h i g h p o i n t s o f t h e r e a r s u r f a c e . D a t u m f e a t u r e M e s t a b - l i s h e s a p l a n e o n t h e h i g h p o i n t s o f t h e l e f t s i d e o f t h e s l o t . D a t u m f e a t u r e K e s t a b l i s h e s a p l a n e o n t h e h i g h p o i n t s o f t w o s u r f a c e s . Datum Features without Size P L 5 H 7 ( 5 / 5 . 0 1 2 ) 1 5 . 9 ± 0 . 2 0 . 2 2 5 ± 0 . 3 M - 1 0 x 1 . 2 5 N M 2 S U R F A C E S K 1 2 . 7 ± 0 . 1 H 2 5 ± 0 . 3 2 X 6 ± 0 . 2 5 S 1 7 ± 0 . 0 2 D a t u m p l a n e s e s t a b l i s h e d f r o m p l a n a r d a t u m f e a t u r e s 6.16

  17. D a t u m f e a t u r e H e s t a b - D a t u m f e a t u r e N e s t a b - l i s h e s a p l a n e o n t h e h i g h l i s h e s a p l a n e o n t h e h i g h p o i n t s o f t h e b o t t o m p o i n t s o f t h e l e f t s u r f a c e . s u r f a c e . D a t u m f e a t u r e L e s t a b - l i s h e s a p l a n e o n t h e h i g h p o i n t s o f t h e r e a r s u r f a c e . D a t u m f e a t u r e M e s t a b - l i s h e s a p l a n e o n t h e h i g h p o i n t s o f t h e l e f t s i d e o f t h e s l o t . D a t u m f e a t u r e K e s t a b l i s h e s a p l a n e o n t h e h i g h p o i n t s o f t w o s u r f a c e s . Datum Features without Size P L 5 H 7 ( 5 / 5 . 0 1 2 ) 1 5 . 9 ± 0 . 2 0 . 2 2 5 ± 0 . 3 M - 1 0 x 1 . 2 5 N M 2 S U R F A C E S K 1 2 . 7 ± 0 . 1 H 2 5 ± 0 . 3 2 X 6 ± 0 . 2 5 S 1 7 ± 0 . 0 2 D a t u m p l a n e s e s t a b l i s h e d f r o m p l a n a r d a t u m f e a t u r e s 6.16

  18. C R 1 5 . 9 ± 0 . 2 5 H 7 ( 5 / 5 . 0 1 2 ) 2 5 ± 0 . 1 M 1 0 x 1 . 2 5 E F A 1 2 . 7 ± 0 . 1 B 2 5 ± 0 . 1 2 X 6 ± 0 . 2 5 S R 8 . 5 0 . 2 M 0 . 4 D G Theory Physical Simulated datum axis E is the axis of a collet, chuck, CMM etc. Datum axis E is the axis of the theoretical datum feature simulator Datum Features of Size 6.18

  19. C R 1 5 . 9 ± 0 . 2 5 H 7 ( 5 / 5 . 0 1 2 ) 2 5 ± 0 . 1 M 1 0 x 1 . 2 5 E F A 1 2 . 7 ± 0 . 1 B 2 5 ± 0 . 1 2 X 6 ± 0 . 2 5 S R 8 . 5 0 . 2 M 0 . 4 D G Datum Features of Size 6.19

  20. C R 1 5 . 9 ± 0 . 2 5 H 7 ( 5 / 5 . 0 1 2 ) 2 5 ± 0 . 1 M 1 0 x 1 . 2 5 E F A 1 2 . 7 ± 0 . 1 B 2 5 ± 0 . 1 2 X 6 ± 0 . 2 5 S R 8 . 5 0 . 2 M 0 . 4 D G Theory Physical D a t u m c e n t e r p l a n e B i s t h e c e n t e r p l a n e o f t h e S i m u l a t e d d a t u m c e n t e r p l a n e B i s d a t u m f e a t u r e s i m u l a t o r . t h e c e n t e r p l a n e o f t h e g a g e b l o c k . Datum Features of Size 6.19

  21. C R 1 5 . 9 ± 0 . 2 5 H 7 ( 5 / 5 . 0 1 2 ) 2 5 ± 0 . 1 M 1 0 x 1 . 2 5 E F A 1 2 . 7 ± 0 . 1 B 2 5 ± 0 . 1 2 X 6 ± 0 . 2 5 S R 8 . 5 0 . 2 M 0 . 4 D G Theory Physical Datum axis C is the axis of the datum feature simulator Simulated datum axis C is the axis of the gage pin Datum Features of Size 6.20

  22. C R 1 5 . 9 ± 0 . 2 5 H 7 ( 5 / 5 . 0 1 2 ) 2 5 ± 0 . 1 M 1 0 x 1 . 2 5 E F A 1 2 . 7 ± 0 . 1 B 2 5 ± 0 . 1 2 X 6 ± 0 . 2 5 S R 8 . 5 0 . 2 M 0 . 4 D G Theory Simulated datum feature D axis and two intersecting planes established from gage Physical Datum D axis and two planes are established from a pattern of two holes Datum Features of Size 6.20

  23. Datum Feature Symbol Placement is Important 6.21

  24. Datum Feature Symbol Placement is Important 6.21

  25. Datum Feature Symbol Placement is Important 6.21

  26. Datum Feature Symbol Placement is Important 6.21

  27. Datum Feature Symbol Placement is Important 6.21

  28. Datum Feature Symbol Placement is Important 6.21

  29. Datum Feature Symbol Placement is Important 6.21

  30. Datum Feature Symbol Placement is Important 6.21

  31. Datum Feature Symbol Placement is Important 6.21

  32. Evaluation specified dimension , orientation planes, axis, center lines, edges, points, areas no three 90 circle X size X X tolerance X X convey rocking X

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