The processing accuracy of precision cnc machining parts is the degree of conformity between the three geometric parameters of the actual size, shape and position of the surface of the processed part and the ideal geometric parameters required by the drawing. Ideal geometric parameters are the average size in terms of size; in terms of surface geometry, they are relative circles, cylinders, planes, cones, straight lines, etc.; in terms of mutual positions between surfaces, they are relatively parallel. , Vertical, coaxial, symmetrical, etc. The processing precision of hardware parts adopts different measurement methods according to different processing precision content and precision requirements. Generally speaking, there are the following types of methods:
1. According to whether the measured parameter is directly measured, it can be divided into direct measurement and indirect measurement.
Direct measurement: directly measure the measured parameter to obtain the measured size. For example, use calipers and comparators to measure. Indirect measurement: Measure the geometric parameters related to the measured size, and obtain the measured size through calculation.
Obviously, direct measurement is more intuitive, while indirect measurement is more cumbersome. Generally, when the measured size or direct measurement fails to meet the accuracy requirements, indirect measurement has to be used.
2. According to whether the reading value of the measuring tool directly represents the value of the measured size, it can be divided into relative measurement and relative measurement.
Relative measurement: The reading value directly indicates the size of the measured size, such as measuring with a vernier caliper.
Relative measurement: The reading value only indicates the deviation of the measured size from the standard quantity. If you use a comparator to measure the diameter of the shaft, you need to adjust the zero position of the instrument with a gauge block first, and then perform the measurement. The measured value is the difference between the diameter of the side shaft and the size of the gauge block. This is a relative measurement. Generally speaking, the relative measurement accuracy is higher, but the measurement is more troublesome.3. According to whether the measured surface is in contact with the measuring head of the measuring instrument, it is divided into contact measurement and non-contact measurement.
Contact measurement: The measuring head is in contact with the touched surface, and there is a mechanical measuring force. Such as measuring parts with a micrometer.
Non-contact measurement: The measuring head does not touch the surface of the part to be measured. Non-contact measurement can avoid the influence of the measuring force on the measurement result. Such as the use of projection method, light wave interferometry and so on. 
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