![Dimensioning and Tolerancing
Design representation:
enough information to
manufacture the part precisely
inspect the manufactured part
[geomtery, dimensions,
tolerances]](https://image.slidesharecdn.com/dandt-240930101612-97f1ac39/85/Geometric-Dimensioning-and-Tolerancing-1-320.jpg)
![Albrecht Durer’s machine [14??AD] (perspective map)](https://image.slidesharecdn.com/dandt-240930101612-97f1ac39/85/Geometric-Dimensioning-and-Tolerancing-6-320.jpg)
![Effect of vanishing point on perspective map
Image on the ‘picture plane’ is a perspective of the 3D object
[Is the object behind in perspective view ?]](https://image.slidesharecdn.com/dandt-240930101612-97f1ac39/85/Geometric-Dimensioning-and-Tolerancing-10-320.jpg)
![0.0006d1/3
0.0006d1/3
-0.001d
Shrink
0.0006d1/3
0.0006d1/3
-0.0005d
Medium Force
0.0006d1/3
0.0006d1/3
-0.00025d
Tight
Interference
[difficult assembly
can transmit torque]
0.0004d1/3
0.0006d1/3
0
Wringing
0.0004d1/3
0.0006d1/3
0
Snug
Transition
[difficult to mfg
precision fit
0.0018d1/3
0.0018d1/3
0.0009d2/3
Medium
0.0013d1/3
0.0013d1/3
0.0014d2/3
Free
0.0025d1/3
0.0025d1/3
0.0025d2/3
Loose
Clearance
[easy assembly,
may vibrate in use]
s (shaft tolerance)
h (hole tolerance)
a (allowance)
Sub-Type
FIT
0.0006d1/3
0.0006d1/3
-0.001d
Shrink
0.0006d1/3
0.0006d1/3
-0.0005d
Medium Force
0.0006d1/3
0.0006d1/3
-0.00025d
Tight
Interference
[difficult assembly
can transmit torque]
0.0004d1/3
0.0006d1/3
0
Wringing
0.0004d1/3
0.0006d1/3
0
Snug
Transition
[difficult to mfg
precision fit
0.0018d1/3
0.0018d1/3
0.0009d2/3
Medium
0.0013d1/3
0.0013d1/3
0.0014d2/3
Free
0.0025d1/3
0.0025d1/3
0.0025d2/3
Loose
Clearance
[easy assembly,
may vibrate in use]
s (shaft tolerance)
h (hole tolerance)
a (allowance)
Sub-Type
FIT
Standard fits](https://image.slidesharecdn.com/dandt-240930101612-97f1ac39/85/Geometric-Dimensioning-and-Tolerancing-25-320.jpg)
![The hole-basic specification convention
shaft hole
2.000
+
-
h
a
s
basic
size
hole basic
unilateral tolerance
clearance fit
+
-
h
a
s
basic
size
hole basic
bilateral tolerance
clearance fit
mean
size
+
-
h
a
s
basic
size
hole basic
unilateral tolerance
interference fit
+
-
h
a
s
basic
size
shaft basic
bilateral tolerance
interference fit
mean
size
+
-
shaft hole
2.000
+
-
h
a
s
basic
size
hole basic
unilateral tolerance
clearance fit
+
-
h
a
s
basic
size
hole basic
bilateral tolerance
clearance fit
mean
size
+
-
h
a
s
basic
size
hole basic
unilateral tolerance
interference fit
+
-
h
a
s
basic
size
shaft basic
bilateral tolerance
interference fit
mean
size
+
-
[Holes are made by drills]](https://image.slidesharecdn.com/dandt-240930101612-97f1ac39/85/Geometric-Dimensioning-and-Tolerancing-26-320.jpg)
Geometric Dimensioning and Tolerancing
- 1. Dimensioning and Tolerancing Design representation: enough information to manufacture the part precisely inspect the manufactured part [geomtery, dimensions, tolerances]
- 2. Projections Theoretical technique to map 3D objects to 2D Dimensions To assist machinist: e.g. distance between centers of holes Tolerances imprecision in machining must specify the tolerance range,
- 3. What is a ‘good level of tolerance’? Designer: tight tolerance is better (less vibration, less wear, less noise) Machinist: large tolerances is better (easier to machine, faster to produce, easier to assemble) Tolerances interchangeability
- 4. Tolerance and Concurrent Engineering Why ? Tolerance specification needs knowledge of accuracy, repeatability of machines process capability …
- 5. Part 1. Projections. 3D models: expensive, difficult to make => need 2D representaitons Images must convey feasible 3D objects
- 6. Albrecht Durer’s machine [14??AD] (perspective map)
- 7. 1. Renaissance architects 2. Modern CAD systems (a) 3D rendering, image processing (b) Mathematics of free-form surfaces (NURBS) Importance of perspective maps
- 8. Why perspective maps ? larger, farther same image size same size, farther smaller image Human sight and perception
- 9. parallel lines converge to a point The vanishing point (or station point)
- 10. Effect of vanishing point on perspective map Image on the ‘picture plane’ is a perspective of the 3D object [Is the object behind in perspective view ?]
- 11. parallel parallel parallel converge: finite vanishing point converge: finite vanishing point parallel parallel parallel parallel parallel converge: finite vanishing point converge: finite vanishing point parallel converge: finite vanishing point converge: finite vanishing point Perspectives and vanishing points Perspectives in mechanical drafting Not good ! (1) parallel lines converge misinterpreted by the machinist (2) Views have too many lines
- 12. Orthographic views A mapping where parallel lines remain parallel How ? Set the vanishing point at infinity Another problem: Back, Sides of object not visible (hidden surfaces) Solution: Multiple views
- 13. Orthographic views: Language of engineering communication
- 14. View direction selection in orthographics Maximize true-size view of most faces FRONT TOP RIGHT FRONT TOP RIGHT
- 15. Isometric view: gives a ‘3D image’ each side has equal length (a) orthograhic (b) top view rotated by 45° (c) Isometric projection each side has equal length (a) orthograhic (b) top view rotated by 45° (c) Isometric projection
- 16. Different types of projections All engineering drawings must be made to scale
- 17. Datum: A theoretical geometric object (point, line, axis, or plane) derived from a specific part/feature of a datum feature on the part. Uses: (1) specify distance of a feature from the datum (2) specify a geometric characteristic (e.g. straightness) of a feature Part 2. ANSI dimensioning
- 18. Basic Dimension: The theoretically exact size of a feature or datum Feature: A geometric entity on the part, (hole, axis, plane, edge) Datum feature: An actual feature of a part, that is used to establish a datum.
- 19. Limits: The max/min allowable sizes Largest allowable size: upper limit Least allowable size: lower limit. LMC (Least Material Condition) MMC (Maximum material Condition)
- 20. Conventions for dimensioning (a) Specify tolerance for all dimensions (b) All necessary , sufficient dimensions X over-dimensioned X X under-dimensioned X Reference dimensions: Redundant dimensions, in ( …) (c) Dimensions should be (i) marked off the datum feature (ii) shown in true-size view (iii) shown in visible view
- 22. (a) Size of a feature Specified by a basic size, and tolerance: 2.50±0.03 upper limit = lower limit = No of digits after decimal precision Part 3. Mechanical Tolerancing Conventional Tolerancing:
- 23. Unilateral and Bilateral Tolerances: 2.50 +0.03 - 0.03 +0.06 + 0.00 2.47 -0.00 -0.06 2.53 2.49 +0.04 - 0.02 bilateral unilateral -0.03 -0.09 2.56 2.50 +0.03 - 0.03 2.50 +0.03 - 0.03 +0.06 + 0.00 2.47 +0.06 + 0.00 2.47 -0.00 -0.06 2.53 -0.00 -0.06 2.53 2.49 +0.04 - 0.02 2.49 +0.04 - 0.02 bilateral unilateral -0.03 -0.09 2.56 -0.03 -0.09 2.56
- 24. (b) The type of fit between mating features Designer needs to specify basic dia, tol of shaft: S±s/2 basic dia, tol of hole: H±h/2 Allowance: a = Dhmin – Dsmax. Conventional Tolerancing..
- 25. 0.0006d1/3 0.0006d1/3 -0.001d Shrink 0.0006d1/3 0.0006d1/3 -0.0005d Medium Force 0.0006d1/3 0.0006d1/3 -0.00025d Tight Interference [difficult assembly can transmit torque] 0.0004d1/3 0.0006d1/3 0 Wringing 0.0004d1/3 0.0006d1/3 0 Snug Transition [difficult to mfg precision fit 0.0018d1/3 0.0018d1/3 0.0009d2/3 Medium 0.0013d1/3 0.0013d1/3 0.0014d2/3 Free 0.0025d1/3 0.0025d1/3 0.0025d2/3 Loose Clearance [easy assembly, may vibrate in use] s (shaft tolerance) h (hole tolerance) a (allowance) Sub-Type FIT 0.0006d1/3 0.0006d1/3 -0.001d Shrink 0.0006d1/3 0.0006d1/3 -0.0005d Medium Force 0.0006d1/3 0.0006d1/3 -0.00025d Tight Interference [difficult assembly can transmit torque] 0.0004d1/3 0.0006d1/3 0 Wringing 0.0004d1/3 0.0006d1/3 0 Snug Transition [difficult to mfg precision fit 0.0018d1/3 0.0018d1/3 0.0009d2/3 Medium 0.0013d1/3 0.0013d1/3 0.0014d2/3 Free 0.0025d1/3 0.0025d1/3 0.0025d2/3 Loose Clearance [easy assembly, may vibrate in use] s (shaft tolerance) h (hole tolerance) a (allowance) Sub-Type FIT Standard fits
- 26. The hole-basic specification convention shaft hole 2.000 + - h a s basic size hole basic unilateral tolerance clearance fit + - h a s basic size hole basic bilateral tolerance clearance fit mean size + - h a s basic size hole basic unilateral tolerance interference fit + - h a s basic size shaft basic bilateral tolerance interference fit mean size + - shaft hole 2.000 + - h a s basic size hole basic unilateral tolerance clearance fit + - h a s basic size hole basic bilateral tolerance clearance fit mean size + - h a s basic size hole basic unilateral tolerance interference fit + - h a s basic size shaft basic bilateral tolerance interference fit mean size + - [Holes are made by drills]
- 27. Generalization of hole-basic/shaft-basic MMC: Maximum material condition LMC: Least material condition Hole at MMC at the lower limit Hole at LMC at the upper limit
- 28. Geometric Tolerancing Y X t t max tol = t 2 Y X t t max tol = t 2 Problems in Conventional tolerancing: (a) Assumes perfect surfaces (b) No use of Datums (c) No specification of form tolerances (d) X±t/2, Y±t/2 rectangular tolerance zone (cylindrical preferred)
- 29. Datums A theoretical feature (e.g. plane, line) Serves as a global coordinate frame for the part during different activities such as design, manufacturing and inspection. Each design must specify the datum planes (or other datums)
- 30. Datum feature The actual plane on the part (imperfect) corresponding to a (perfect) datum plane datum feature A datum plane A datum feature B datum plane B datum A datum B datum C datum feature A datum plane A datum feature B datum plane B datum feature B datum plane B datum A datum B datum C datum A datum B datum C Sequence of establishing datums: PRIMARY (3 points) SECONDARY (2 points) TERTIARY (1 point)
- 31. ANSI symbols for geometric tolerancing True Position Location Total runout Circular runout Runout Concentricity Parallel Perpendicular Angle Orientation Surface profile Line profile Profile Cylindricity Circularity Flatness Straightness Form Symbol Characteristic Type of Tolerance True Position Location Total runout Circular runout Runout Concentricity Parallel Perpendicular Angle Orientation Surface profile Line profile Profile Cylindricity Circularity Flatness Straightness Form Symbol Characteristic Type of Tolerance MMC Arc length Reference size Spherical Radius Radius Spherical Diameter Diameter Projected Tol Zone LMC Regardless of feature size ANSI modification symbols MMC Arc length Reference size Spherical Radius Radius Spherical Diameter Diameter Projected Tol Zone LMC Regardless of feature size ANSI modification symbols M M S S L L P P S S R SR ( )
- 32. 3.00 -A- symbol tolerance modifier datum modifier 0.001 M M A datum basic size symbol tolerance primary- secondary- tertiary datum 0.001 A B C 3.00 -A- symbol tolerance modifier datum modifier 0.001 M M A symbol tolerance modifier datum modifier 0.001 M M A 0.001 M M M M A datum basic size symbol tolerance primary- secondary- tertiary datum 0.001 A B C symbol tolerance primary- secondary- tertiary datum 0.001 A B C Different allowed notations (ANSI)
- 33. Location tolerances: Conventional system: rectangular tolerance zones True Position Tolerancing circular (cylindrical) tolerance zone
- 34. Form Tolerances
- 35. Form Tolerances
- 36. Form Tolerances