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Dimensioning and Tolerancing

Dimensioning and Tolerancing. By Siddhalingeshwar I.G. M.Tech . ANSI Y14.5-1994 Standard. This standard establishes uniform practices for defining and interpreting dimensions, and tolerances, and related requirements for use on engineering drawings.

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Dimensioning and Tolerancing

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  1. Dimensioning and Tolerancing By Siddhalingeshwar I.G. M.Tech. Metrology by IGS

  2. ANSI Y14.5-1994 Standard This standard establishes uniform practices for defining and interpreting dimensions, and tolerances, and related requirements for use on engineering drawings. The figures in this presentation are taken from Bruce Wilson’s Design Dimensioning and Tolerancing. Metrology by IGS

  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) Metrology by IGS

  4. Tolerancing application: an example The type of fit between mating features Designer needs to specify: basic diameter and the tolerance of shaft: S±s/2 basic diameter and the tolerance of hole: H±h/2 Allowance: a = Dhmin – Dsmax. Metrology by IGS

  5. Fit Between Parts • Clearance fit: The shaft maximum diameter is smaller than the hole minimum diameter. • Interference fit: The shaft minimum diameter is larger than the hole maximum diameter. • Transition fit: The shaft maximum diameter and hole minimum have an interference fit, while the shaft minimum diameter and hole maximum diameter have a clearance fit Clearance Fit Interference Fit Transition Fit Metrology by IGS

  6. Classes of Fit The limits to sizes for various types of fit of mating parts are defined by the standard ANSI B4.1 There are five basic classes of fit: Running and sliding clearance (RC)--there are type of RC fits, RC1-RC9; Location clearance (LC)--there are eleven types of LC fits; Location transition (LT)--there are six types of LT fits; Location interference (LN)--there are three LN fits; Force fits (FN)--there are five FN fits. Metrology by IGS

  7. nominal dimension + means a range 0.95 - 1.05 1.00 0.05 - tolerance + 0.10 - 0.00 + 0.00 - 0.10 0.95 1.05 unilateral bilateral + 1.00 0.05 - Unilateral and Bilateral Tolerances: Metrology by IGS

  8. Overview of Geometric Tolerances Geometric tolerances define the shape of a feature as opposed to its size. We will focus on three basic types of dimensional tolerances: Form tolerances: straightness, circularity, flatness, cylindricity; Orientation tolerances; perpendicularity, parallelism, angularity; Position tolerances: position, symmetry, concentricity. Metrology by IGS

  9. Metrology by IGS

  10. Feature Control Frame A geometric tolerance is prescribed using a feature control frame. It has three components: 1. the tolerance symbol, 2. the tolerance value, 3. the datum labels for the reference frame. Metrology by IGS

  11. 1.22 ' 0.83 ' 0.95 ' 3.03 ' 1.72 ' 0.86 ' 1.22 ' 0.83 ' 3.03 ' Dimensioning Requirements 1. Unambiguous 2. Completeness 3. No redundancy Incomplete dimensioning Redundant dimensioning Adequate dimensioning Metrology by IGS

  12. Tolerancing Metrology by IGS

  13. 0.80 ' ±0.01 1.20 ' ±0.01 1.00 ' ±0.01 ? "TOLERANCE IS ALWAYS ADDITIVE" What is the expected dimension and tolerances? d = 0.80 +1.00 + 1.20 = 3.00 t = ± (0.01 + 0.01 + 0.01) = ± 0.03 Metrology by IGS

  14. x ? 0.80 ' ±0.01 1.20 ' ±0.01 3.00 ' ±0.01 Maximum x length = 3.01 - 0.79 - 1.19 = 1.03 Minimum x length = 2.99 - 0.81 - 1.21 = 0.97 Therefore x = 1.00 ± 0.03 Metrology by IGS

  15. Order of Precedence • The part is aligned with the datum planes of a reference frame using 3-2-1 contact alignment. • 3 points of contact align the part to the primary datum plane; • 2 points of contact align the part to the secondary datum plane; • 1 point of contact aligns the part with the tertiary datum plane Metrology by IGS

  16. Straightness of a shaft Metrology by IGS

  17. Straightness of a Shaft • A shaft has a size tolerance defined for its fit into a hole. A shaft meets this tolerance if at every point along its length a diameter measurement fall within the specified values. • This allows the shaft to be bent into any shape. A straightness tolerance on the shaft axis specifies the amount of bend allowed. • Add the straightness tolerance to the maximum shaft size (MMC) to obtain a “virtual condition” Vc, or virtual hole, that the shaft must fit to be acceptable. Metrology by IGS

  18. Straightness of a Hole • The size tolerance for a hole defines the range of sizes of its diameter at each point along the centerline. This does not eliminate a curve to the hole. • The straightness tolerance specifies the allowable curve to the hole. • Subtract the straightness tolerance from the smallest hole size (MMC) to define the virtual condition Vc, or virtual shaft, that must fit the hole for it to be acceptable. Metrology by IGS

  19. Straightness of a Center Plane • The size dimension of a rectangular part defines the range of sizes at any cross-section. • The straightness tolerance specifies the allowable curve to the entire side. • Add the straightness tolerance to the maximum size (MMC) to define a virtual condition Vc that the part must fit into in order to meet the tolerance. Metrology by IGS

  20. 1.000 ' ±0.002 Flatness 0 . 0 0 1 Tolerance zone defined by two parallel planes. p a r a l l e l p l a n e s 0 . 0 0 1 Metrology by IGS

  21. Flatness Metrology by IGS

  22. Flatness, Circularity and Cylindricity Flatness Circularity Cylindricity • The flatness tolerance defines a distance between parallel planes that must contain the highest and lowest points on a face. • The circularity tolerance defines a pair of concentric circles that must contain the maximum and minimum radius points of a circle. • The cylindricity tolerance defines a pair of concentric cylinders that much contain the maximum and minimum radius points along a cylinder. Metrology by IGS

  23. Circularity (Roundness) Metrology by IGS

  24. 1.00 ' ±0.05 Cylindricity Tolerance zone bounded by two concentric cylinders within which the cylinder must lie. 0 . 0 1 Rotate in a V 0 . 0 1 Rotate between points Metrology by IGS

  25. Parallelism Metrology by IGS

  26. Parallelism Tolerance • A parallelism tolerance is measured relative to a datum specified in the control frame. • If there is no material condition (ie. regardless of feature size), then the tolerance defines parallel planes that must contain the maximum and minimum points on the face. • If MMC is specified for the tolerance value: • • If it is an external feature, then the tolerance is added to the maximum dimension to define a virtual • condition that the part must fit; • If it is an internal feature, then the tolerance is subtracted to define the maximum dimension that must fit into the part. Metrology by IGS

  27. Perpendicularity • A perpendicular tolerance is measured relative to a datum plane. • It defines two planes that must contain all the points of the face. • A second datum can be used to locate where the measurements are taken. Metrology by IGS

  28. Perpendicular Shaft, Hole, and Center Plane Center Plane Hole Shaft • Shaft: The maximum shaft size plus the tolerance defines the virtual hole. • Hole: The minimum hole size minus the tolerance defines the virtual shaft. • Plane: The tolerance defines the variation of the location of the center plane. Metrology by IGS

  29. Angularity • An angularity tolerance is measured relative to a datum plane. • It defines a pair planes that must • contain all the points on the angled face of the part, or • if specified, the plane tangent to the high points of the face. Metrology by IGS

  30. A .007 .007 Tolerance Zone A YY XX Concentricity Tolerance Note This cylinder (the right cylinder) must be concentric within .007 with the Datum A (the left cylinder) as measured on the diameter What It Means Metrology by IGS

  31. T o l e r a n c e z o n e 0 . 0 1 d i a True Position Dimensional tolerance Hole center tolerance zone O . 8 0 ± 0 . 0 2 O 0 . 0 1 M A B True position tolerance 1 . 0 0 B 1 . 2 0 A Metrology by IGS

  32. Position Tolerance for a Hole • The position tolerance for a hole defines a zone that has a defined shape, size, location and orientation. • It has the diameter specified by the tolerance and extends the length of the hole. • Basic dimensions locate the theoretically exact center of the hole and the center of the tolerance zone. • Basic dimensions are measured from the datum reference frame. Metrology by IGS

  33. 20.06 Maximum Envelope 0.06 Maximum Allowable Curvature 20.00 Maximum Allowable Diameter Virtual Condition Envelope All Required Tolerances Metrology by IGS

  34. Surface Finish w a v i n e s s r o u g h n e s s r o u g h n e s s w i d t h w a v i n e s s w i d t h Metrology by IGS

  35. B Profile 0 . 0 0 5 A B 0 . 0 0 1 A A uniform boundary along the true profile within which the elements of the surface must lie. Metrology by IGS

  36. D e v i a t i o n o n e a c h c i r c u l a r c h e c k r i n g i s l e s s t h a n t h e D a t u m t o l e r a n c e . a x i s Runout A composite tolerance used to control the functional relationship of one or more features of a part to a datum axis. Circular runout controls the circular elements of a surface. As the part rotates 360° about the datum axis, the error must be within the tolerance limit. Metrology by IGS

  37. Total Runout D e v i a t i o n o n t h e t o t a l s w e p t w h e n t h e p a r t i s r o t a t i n g D a t u m i s l e s s t h a n t h e a x i s t o l e r a n c e . Metrology by IGS

  38. Runout Metrology by IGS

  39. Geometric Tolerancing - Definitions • Maximum Material Condition (MMC) – The condition in which a feature of size contains the maximum amount of material with the stated limits of size, - fore example, minimum hole diameter and maximum shaft diameter • Least Material Condition (LMC) – Opposite of MMC, the feature contains the least material. For example, maximum hole diameter and minimum shaft diameter • Virtual Condition – The envelope or boundary that describes the collective effects of all tolerance requirements on a feature. Metrology by IGS

  40. MMC Hole Given the same peg (MMC peg), when the produced hole size is greater than the MMC hole, the hole axis true position tolerance zone can be enlarged by the amount of difference between the produced hole size and the MMC hole size. , Metrology by IGS

  41. Tolerance Value Modification Produced True Pos tol hole size 0.97 out of diametric tolerance 0.98 0.01 0.05 0.01 0.99 0.02 0.04 0.01 1.00 0.03 0.03 0.01 1.01 0.04 0.02 0.01 1.02 0.05 0.01 0.01 1.03 out of diametric tolerance M L S B MMC LMC A The default modifier for true position is MMC. For M the allowable tolerance = specified tolerance + (produced hole size - MMC hole size) Metrology by IGS

  42. METROLOGY & MEASUREMENTS Thank You Metrology by IGS

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