Tolerance and fit with 67 knowledge points

2019-03-15 12:22:45 9

1. What is called tolerance?

A: Allowing variations in part size and geometry parameters is called tolerance.


2. What is called size?

A: A number that represents the length value in a specific unit.


3. What is called the basic size?

A: Make the design a given size.


4. What is the actual size?

A: It is the size obtained by measurement.


5. What is the limit size?

A: Refers to the two limits that allow for dimensional changes.


6. What is called Maximum Entity Status (MMC) and Maximum Entity Size?

A: The maximum solid state refers to the state in which the hole or shaft is within the dimensional tolerance range and has the largest amount of material. The size in this state, called the maximum physical size, is a general term for the minimum limit size of the hole and the maximum limit size of the shaft.


7. What is called the minimum entity state (LMC for short) and the minimum physical size?

A: The minimum solid state refers to the state in which the hole or shaft is within the dimensional tolerance and has the least material. The size in this state, called the minimum physical size, is a general term for the maximum limit size of the hole and the minimum limit size of the shaft.


8. What is the size of the action?

A: The maximum ideal shaft size that is connected to the actual hole over the entire length of the mating surface is called the effective size of the hole. The size of the smallest ideal hole circumscribing the actual axis is called the effective size of the shaft.


9. What is called dimensional deviation?

A: It refers to the algebraic difference obtained from a certain size minus its basic size.


10. What is called dimensional tolerance?

A: It refers to the amount of change in the allowable size.


11. What is the zero line?

A: In the tolerance and mating diagram (referred to as the tolerance band diagram), determine a reference line of the deviation, that is, the zero deviation line.


12. What is the tolerance band?

A: In the tolerance zone diagram, an area defined by two straight lines representing the upper and lower deviations.


13. What is the basic deviation?

A: It is used to determine the upper or lower deviation of the tolerance zone relative to the neutral position, generally referring to the deviation from the zero line. When the tolerance band is above the zero line, the basic deviation is the lower deviation; when it is below the zero line, the basic deviation is the upper deviation.


14. What is called standard tolerance?

A: Any tolerance specified by the national standard to determine the tolerance band size.


15. What is called cooperation?

A: Refers to the relationship between the hole and the shaft tolerance band of the same basic size.


16. What is the base hole system?

A: It is the tolerance band of the hole with a basic deviation, and the tolerance band of the axis with different basic deviations is formed.


17. What is the basic axis system?

A: It is a system in which the basic deviation is a certain tolerance zone of the shaft, and the tolerance zone of the hole with different basic deviations forms various cooperations.


18. What is the fit tolerance?

A: It is the variation of the allowable gap. It is equal to the absolute value of the algebraic difference between the maximum gap and the minimum gap. It is also equal to the sum of the hole tolerance band and the shaft tolerance band.


19. What is called clearance fit?

A: The tolerance band of the hole is completely above the tolerance band of the shaft, ie the fit with clearance (including the fit with a minimum clearance equal to zero).


20. What is called an interference fit?

A: The tolerance band of the hole is completely below the tolerance band of the shaft, ie it has an interference fit (including a fit with a minimum interference equal to zero).


21. What is called transition fit?

Answer: In the cooperation between the hole and the shaft, the tolerance bands of the hole and the shaft overlap each other. Any one of the holes and the shaft may match, and may have a gap or an interference fit.


22. What is the preferred blending characteristic when the base hole is made of H11/c11 or the base shaft is made of C11/h11?

A: The gap is very large, it is used for very loose, slow-moving dynamic fits; exposed components requiring large tolerances and large gaps; loose fittings that require easy assembly. Equivalent to the old national standard D6/dd6.


23. What is the priority fit characteristic when the base hole is made of H9/d9 or the base shaft is made of D9/h9?

A: A freely-rotating fit with a large clearance for non-critical requirements, or when there is large temperature variation, high rotational speed or large journal pressure. Equivalent to the old national standard D4/de4.


24. What is the priority fit characteristic when the base hole is made of H8/f7 or the base shaft is made of F8/h7?

A: The small rotation fit is used for precise rotation of medium and medium journal pressures; it is also used for easy intermediate positioning. Equivalent to the old national standard D/dc.


25. What is the priority fit characteristic when the base hole is made of H7/g6 or the base shaft is made of G7/h6?

A: The sliding fit with a small clearance is used for undesired positioning and positioning when it is used for undesired free rotation but freely movable and sliding and requires precise positioning. Equivalent to the old national standard D/db.


26. The base hole is made of H7/h6; H8/h7; H9/h9; H11/h11 or base shaft is made of H7/h6; H8/h7; H9/h9; H11/h11, the preferred compounding property is what?

Answer: All the gaps are positioned and matched, the parts can be freely assembled and disassembled, and the work is generally relatively stationary. The gap under the maximum solid condition is zero, and the gap under the minimum solid condition is determined by the tolerance level. H7/h6 is equivalent to the old national standard D/d; H8/h7 is equivalent to the old national standard D3/d3; H9/h9 is equivalent to the old national standard D4/d4; H11/h11 is equivalent to the old national standard D6/d6.


27. What is the priority fit characteristic when the base hole is made of H7/h6 or the base shaft is made of K7/h6?

A: Transitional coordination for precise positioning. Equivalent to the old national standard D/gc.


28. What is the priority fit characteristic when the base hole is made of H7/n6 or the base shaft is made of N7/h6?

A: The transition fit allows for more precise positioning with greater interference. Equivalent to the old national standard D/ga.


29. What is the priority fit characteristic when the base hole is made of H7/p6 or the base shaft is made of P7/h6?

Answer: Interference positioning is a small interference fit. When the positioning accuracy is particularly important, the rigidity and alignment requirements of the components can be achieved with the best positioning accuracy. However, there is no special requirement for the internal bore with pressure. The tightness of the fit conveys the friction load. Equivalent to the old national standard D/ga~D/jf. Where H7 is less than or equal to 3 mm is a transition fit.


30. What is the priority fit characteristic when the base hole is made of H7/s6 or the base shaft is made of S7/h6?

A: Medium press fit, suitable for general steel parts; or for cold shrink fit of thin-walled parts, for the tightest fit of cast iron parts, equivalent to the old national standard D/je.


31. What is the priority fit characteristic when the base hole is made of H7/u6 or the base shaft is made of U7/h6?

Answer: Press fit, suitable for parts that can be pressed with large force or cold shrink fit that should not withstand large press-in force.


32. What is the matching characteristic when the basic deviation of the axis is a; b?

Answer: It is a clearance fit, which can get a particularly large gap and is rarely used.


33. What is the fit characteristic when the basic deviation of the axis is c?

Answer: It is a clearance fit, which can get a large gap. It is generally suitable for slow and slack dynamic fit. For poor working conditions (such as agricultural machinery), deformation, or for ease of assembly, the surface must be guaranteed to have a large gap. It is recommended to cooperate with H11/c11, and its higher level of cooperation, such as H8/c7, is suitable for the tight dynamic cooperation of one shaft working at high temperature, such as exhaust valve and conduit of internal combustion engine.


34. What is the mating characteristic when the basic deviation of the axis is d?

Answer: It is a clearance fit. It is generally used for IT7~IT11. It is used for loose rotation, such as sealing cover, pulley, idle pulley and so on. It is suitable for large-diameter sliding bearing mating, such as turbines, ball mills, roll forming and heavy bending machines, and some sliding supports in other heavy machinery.


35. What is the mating characteristic when the basic deviation of the axis is e?

Answer: It is a clearance fit. It is mostly used for IT7~IT9. It is usually suitable for support joints that require obvious clearance and easy to rotate, such as large span and multi-support. The high-grade e-axis is suitable for large, high-speed and heavy loads. Supporting fits, such as worm gear generators, large motors, internal combustion engines, camshafts and rocker arms.


36. What is the fit characteristic when the basic deviation of the axis is f?

Answer: It is a clearance fit, which is mostly used for the general rotation coordination of IT6~IT8. When the temperature is not greatly affected, it is widely used for the lubrication of ordinary lubricating oil (fat), such as the cooperation of the rotating shaft of the gear box, small motor, pump, etc. with the sliding bearing.


37. What is the fit characteristic when the basic deviation of the axis is g?

Answer: It is a clearance fit, the clearance is small, the manufacturing cost is high, and it is not recommended for the rotary fit except for the delicate device with very light load. It is mostly used in IT5~IT7 grades. It is most suitable for precision sliding fit without rotation. It is also used for positioning and matching such as bolts, such as precision connecting rod bearings, pistons, slide valves and connecting rod pins.


38. What is the mating characteristic when the basic deviation of the axis is h?

A: It is a gap fit, mostly used for IT4~IT11. It is widely used for parts without relative rotation. As a general positioning fit, it is also used for precision sliding fit without temperature deformation.


39. What is the mating characteristic when the basic deviation of the axis is js?

A: It is a transitional fit, which is a completely symmetric deviation (+IT/2). The average is a slightly clearance fit, mostly for IT4-7, requiring clearances smaller than the h-axis and allowing for slightly interference positioning (such as couplings) that can be assembled with a hand or a wooden hammer.


40. What is the mating characteristic when the basic deviation of the axis is k?

A: It is a transitional fit, with an average of no gaps, suitable for IT4-IT7. It is recommended for positioning and fitting with slight interference. The inverted table is used to eliminate the positioning and coordination of vibration. Usually assembled with a wooden hammer.


41. What is the fit characteristic when the basic deviation of the axis is m?

A: It is a transitional coordination, with an average of small transitions. Applicable to IT4I-T7, assembled with a hammer or press, usually recommended for tight component fit. H6/n5 is an interference fit when mated.


42. What is the mating characteristic when the basic deviation of the axis is n?

A: It is a transitional fit. The average interference is slightly larger than the m-axis. There is very little gap. It is suitable for IT4-IT7. It is assembled with a hammer or a press. It is usually recommended for tight component fit. H6/n5 is an interference fit when mated.


43. What is the mating characteristic when the basic deviation of the axis is p?

Answer: It is an interference fit. When it is matched with H6 or H7, it is an interference fit. When it is matched with H8 hole, it is a transition fit. For non-ferrous parts, a lighter press-fit fits and is easy to remove when needed. For steel, cast iron or copper, steel assembly is a standard press fit.


44. What is the fit characteristic when the basic deviation of the axis is r?

A: It is an interference fit. It is a medium fit for iron parts. For non-ferrous parts, it can be disassembled when needed. Cooperate with H8 hole, the interference fit is more than 100mm in diameter, and the diameter is small for transition fit.


45. What is the fit characteristic when the basic deviation of the axis is s?

A: An interference fit for permanent and semi-permanent assembly of steel and iron parts. Can produce considerable bonding force. When an elastic material such as a light alloy is used, the compounding property is equivalent to the P axis of the iron component. For example, the collar is press-fitted on the shaft, the valve seat, and the like. When the size is large, in order to avoid damage to the mating surface, thermal expansion or cold shrink assembly is required.


46. The basic deviation of the axis is t; u; v; x; y; z, what is the mating characteristic?

A: It is an interference fit, and the amount of interference increases in turn, which is generally not recommended.


47. When is the base shaft system selected?

A: Directly use cold drawn steel that is manufactured to the tolerance zone of the reference axis and has a certain tolerance level (generally 8 to 11) and is no longer machined. At this point, different hole tolerance band positions can be selected to create a variety of different fit requirements. In agricultural machinery and textile machinery, this situation is more.


It is much more difficult to machine a precision shaft with a size of less than 1 mm than to machine a hole of the same level. Therefore, in the instrument manufacturing, watch production, radio and electronics industries, it is common to use a thin steel wire that has been tempered to form a shaft. The shaft system is better than the base hole system.


From the structural point of view, one shaft is matched with several holes in different parts, and each has different fitting requirements. In this case, the base shaft should be considered.


48. How does it work with standard parts?

A: If it is matched with the standard parts, the standard part should be used as the reference part to determine the matching system.

For example, in the rolling bearing support structure, the cooperation of the outer ring of the rolling bearing and the hole of the box should be made by the base shaft. The cooperation between the inner ring of the bearing and the journal should be made by the base hole, the hole of the box is made according to J7, and the journal is made by k6.


49. What is the range of tolerance levels for the grinding method?

A: IT1~IT5 should be taken.


50. What is the range of tolerance levels that should be taken?

A: IT4~IT7 should be taken.


51. What is the scope of tolerance for diamond car processing?

A: IT5~IT7 should be taken.


52. What is the range of tolerance levels for diamond boring?

A: IT5~IT7 should be taken.


53. What is the range of tolerance levels for round grinding?

A: IT5~IT8 should be taken.


54. What is the range of tolerance levels for the flat grinding method?

A: IT5~IT8 should be taken.


55. What is the range of tolerance levels for broaching?

A: IT5~IT8 should be taken.


56. What is the scope of the tolerance class?

A: IT7~IT9 should be taken.


57. What is the range of tolerance levels for reaming?

A: IT6~IT10 should be taken.


58. What is the range of tolerance levels for milling?

A: IT8~IT11 should be taken.


59. What is the range of tolerance levels for planing and inserting?

A: IT10~IT11 should be taken.


60. What is the range of tolerance levels for rolling and extrusion processing?

A: IT10~IT11 should be taken.


61. What is the range of tolerance levels for roughing?

A: IT10~IT12 should be taken.


62. What is the range of tolerance levels for rough machining?

A: IT10~IT12 should be taken.


63. What is the range of tolerance levels for drilling methods?

A: IT10~IT13 should be taken.


64. What is the range of tolerance levels for stamping?

A: IT10~IT14 should be taken.


65. What is the range of tolerance class for sand casting?

A: IT14~IT15 should be taken.


66. What is the range of tolerance class for metal casting?

A: IT14~IT15 should be taken.


67. What is the range of tolerance levels for forging processing?

A: IT15~IT16 should be taken.