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Main aspects affecting machining accuracy

Update:15-11-2019
Summary:

1, dimensional accuracy Refers to the degree of conform […]

1, dimensional accuracy
Refers to the degree of conformity between the actual size of the machined part and the tolerance of the part size.
Dimensional accuracy is controlled by dimensional tolerances. Dimensional tolerances are the allowable variations in the dimensions of the part during machining. In the case of the same basic dimensions, the smaller the dimensional tolerance, the higher the dimensional accuracy.
2, shape accuracy
Refers to the degree to which the actual geometry of the surface of the finished part matches the ideal geometry. The items for evaluating the shape accuracy include six items such as straightness, flatness, roundness, cylindricity, and line outline. The shape accuracy is controlled by the shape tolerance. The shape tolerances are divided into 12 precision grades except for the roundness and cylindricity. Level 1 is the highest and level 12 is the lowest.
3, positional accuracy
Refers to the difference in actual positional accuracy between the surfaces of the parts after machining. The items for assessing positional accuracy include eight items: parallelism, verticality, inclination, concentricity, symmetry, position, round runout, and full runout. Position accuracy is controlled by positional tolerances, and the positional tolerances of each item are also divided into 12 accuracy levels.
Relationship between dimensional accuracy, shape accuracy and positional accuracy
Generally, when designing machine parts and specifying the machining accuracy of parts, care should be taken to control the shape error within the position tolerance, and the position error should be smaller than the dimensional tolerance. That is, the important surface of precision parts or parts, the shape accuracy requirements should be higher than the position accuracy requirements, and the position accuracy requirements should be higher than the dimensional accuracy requirements.

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