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FITS and TOLERANCES

FITS and TOLERANCES. C ontrol M easurements of F inished P arts. Indicating the Desired Dimension. Indication of the Real Dimension of Parts. Due to the inevitable inaccuracy of manufacturing methods, a part cannot be made precisely to a given dimension.

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FITS and TOLERANCES

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  1. FITS and TOLERANCES

  2. Control Measurements of Finished Parts

  3. Indicating the Desired Dimension

  4. Indication of the Real Dimension of Parts Due to the inevitable inaccuracy of manufacturing methods, a part cannot be made precisely to a given dimension.

  5. Indication of the Real Dimension of Parts

  6. Indication of the Real Dimension of Parts

  7. Selection of Waste Parts

  8. Selection of Waste Parts Waste results when the manufacturing process cannot maintainsize within prescribed limits.

  9. Selection of Acceptable Parts

  10. Selection of Acceptable Parts There is no such thing as an "exact size".

  11. Important Terms – Single Part • Nominal Size – general size, usually expressed in mms • Actual Size – measured size of the finished part • Limits – maximum and minimum sizes shown by tolerances (larger value is the upper limit and the smaller value is the lower limit) • Tolerance – total allowable variance in dimensions (upper limit – lower limit) – object dimension could be as big as the upper limit or as small as the lower limit or anywhere in between.

  12. Characteristics of Tolerances

  13. Characteristics of Tolerances Connection btw the characteristics: US = N + UD LS = N – LD T = US – LS =

  14. The Possible Positions of the Tolerance Zone

  15. The tolerance zone is above the zero (base) line

  16. The tolerancezone is onthezero (base) line

  17. The tolerance zone is under the zero (base) line

  18. Possible positions of the tolerance zone in case of shafts ISO standard uses toleranceposition letters with lowercase letters for the shafts. Fundamental Deviation:is the deviation closest to the basic size.

  19. FYI: The ISO System of Limits and Fits (referred to as the ISO system) is covered in national standards throughout the world, asshown by the following list: • Global ISO 286 • USA ANSI B4.2 • Japan JIS B0401 • Germany DIN 7160//61 • France NF E 02-100-122 • UK BSI 4500 • Italy UNI 6388 • Australia AS 1654

  20. Possible positions of the tolerance zone in the case of holes ISO standard uses toleranceposition letters with capital letters for the holes. Fundamental Deviation:is the deviation closest to the basic size.

  21. Schematic representation of the placement of the tolerance interval

  22. A tűrésnagyság szabványos értékei

  23. IT: International Tolerance

  24. Example: A shaft of nominal diameter 25 mm is going to be manufactured.IT grade is required to be IT7. • Determine the tolerance on the shaft.

  25. Fits Between Mating Parts

  26. ILLUSTRATION OF DEFINITIONS

  27. Fits Between Mating Parts Fit: degree of tightness between two parts. Fit types: • Clearance Fit– tolerance of mating parts always leaves a space • Interference Fit– tolerance of mating parts always results in interference • Transition Fit– sometimes interferes, sometimes clears

  28. Clearance Fit The mating parts have such upper and lower limits that a clearance alwaysresults when the mating parts are assembled.

  29. Clearance Fit (e.g.: H7/f6)

  30. Clearance Fit(pl. H7/f6)

  31. Clearance Fit(pl. H7/f6)

  32. Transition Fit Either a clearance or an interference may result depending on the exact valueof the dimensions of the machined shaft and hole within thespecified tolerancezones.

  33. Transition Fit(e.g.: H7/j6)

  34. Transition Fit(e.g.: H7/j6)

  35. Transition Fit(e.g.: H7/j6)

  36. Transition Fit(e.g.: H7/j6)

  37. Interference Fit The mating parts have such limits that the lowest shaft diameter is larger than thelargest hole diameter..

  38. Interference Fit(e.g. H7/p6)

  39. Interference Fit(e.g. H7/p6)

  40. Interference Fit(e.g. H7/p6)

  41. Basic Systems for Fit Specification In order to standardize dimensioning of fits, two basic systems are used: • Basic Hole System: Minimum hole diameter is taken as the basis. Lower deviation for thehole is equal to zero. Dmax is prescribed according to the specifiedtolerance. • Basic Shaft System: Maximum shaft diameter is taken as the basis. Upper deviation for theShaft is equal to zero. dmin is prescribed according to the specifiedtolerance.

  42. Basic Hole System • Toleranced dimensions are commonly determined using the basic hole system in which the minimum hole size is taken as the basic size.

  43. Fits in Basic Hole System

  44. Basic Shaft System • In this system, the maximum shaft is taken as the basic size and is used only in specific circumstances.

  45. Fits in Basic Shaft System

  46. Indicating Tolerances

  47. Two ways of indicating tolerances on technical drawings Limitsof a dimension or the tolerance values are specified directly with the dimension. Questions ?

  48. Indicating tolerances The dimension is given by: • a shape symbol, • nominal size, • a letter indicating the position of the tolerance zone in relation to zero line, • a number indicating the width of the tolerance zone. (quality of production?)

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