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# What Are the Measurement Methods of Precision Parts Processing Precision?

## Ⅰ. What is machining precision

Machining precision is the degree of conformity between the actual size, shape and position of the three geometric parameters of the surface of the processed part and the ideal geometric parameters required by the drawing. Ideal geometric parameters are average sizes; for surface geometry, they are absolute circles, cylinders, planes, cones, and straight lines; for mutual positions between surfaces, they are absolutely parallel, vertical, coaxial, symmetrical, etc. The deviation of the actual geometric parameters of the part from the ideal geometric parameters is called the machining error. Our precision machining is based on machine tool spindle, rotary thimble, lead screw, shaft machining, CNC lathe machining and tool holder! The quality is guaranteed.

## Ⅱ. Measuring methods of machining precision

According to different processing precision content and precision requirements, different measurement methods are used. Generally speaking, there are the following types of methods:

1. The machining precision measurement can be divided into direct measurement and indirect measurement.

Direct measurement: directly measure the 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 size through calculation.

Obviously, direct measurement is more intuitive, and indirect measurement is more cumbersome. Generally, when the measured size or direct measurement fails to meet the precision requirements, indirect measurement has to be used.

2. Precision machining can be divided into absolute measurement and relative measurement according to whether the reading value of the measuring tool directly represents the value of the measured size.

Absolute 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 measured shaft and the size of the gauge block. This is a relative measurement. Generally speaking, the relative measurement precision is higher, but the measurement is more troublesome.

3. The machining precision is divided into contact measurement and non-contact measurement according to whether the measured surface is in contact with the measuring head of the measuring instrument.

Contact measurement: The measuring head is in contact with the surface to be touched, and there is a precise measuring force, such as measuring parts with a micrometer.

Non-contact measurement: The measuring head is not in contact with the surface of the measured part. 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.

4. Precision machining is divided into single measurement and comprehensive measurement according to the number of measurement parameters at a time.

Single measurement: measure each parameter of the tested part separately.

Comprehensive measurement: measure the comprehensive index reflecting the relevant parameters of the part. For example, when measuring the thread with a tool microscope, the actual pitch diameter of the thread, the half-angle error of the tooth profile, and the cumulative error of the thread pitch can be measured separately.

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