Precision machining is achieved using precision machine tools, measuring tools, and instruments under strictly controlled environmental conditions. Processing accuracy reaching or exceeding 0.1 microns is called ultra precision machining. In the aerospace industry, precision machining is mainly used to process precision mechanical parts in aircraft control equipment, such as precision fittings in hydraulic and pneumatic servo mechanisms, frames and shells of gyroscopes, air and liquid floating bearing components, and floats. The structure of precision parts for aircraft is complex, with low stiffness and high precision requirements, and a large proportion of difficult to machine materials. The process effect of precision machining is: ① The geometric shape and mutual position accuracy of the parts reach the micrometer or arcsecond level; ② The boundary or characteristic dimension tolerance of the parts is below micrometers; ③ The micro roughness of the part surface (average height difference of surface roughness) is less than 0.1 microns; ④ Mutual accessories can meet the requirements of mating force; ⑤ Some parts can also meet precise mechanical or other physical property requirements, such as the torsional stiffness of the float gyroscope torsion bar and the stiffness coefficient of the flexible element.

Precision machining mainly includes processes such as precision turning, precision boring, precision milling, precision grinding, and grinding. ① Precision machining and boring: Most precision light alloy (aluminum or magnesium alloy, etc.) parts of aircraft are processed using this method. Generally, natural single crystal diamond cutting tools are used, with a blade radius of less than 0.1 micrometers. Processing on high-precision lathes can achieve a precision of 1 micron and surface roughness with an average height difference of less than 0.2 microns, with a coordinate accuracy of ± 2 microns. ② Precision milling: used for processing aluminum or beryllium alloy structural components with complex shapes. Relying on the precision of the machine tool's guide rails and spindle to achieve high mutual positional accuracy. Using carefully ground diamond cutting heads for high-speed milling can obtain precise mirror surfaces. ③ Precision grinding: used for machining shaft or hole parts. Most of these parts are made of quenched steel, which has high hardness. Most high-precision grinding machine spindles use static or dynamic pressure liquid bearings to ensure high stability. The ultimate precision of grinding is not only affected by the stiffness of the machine tool spindle and bed, but also by factors such as the selection and balance of the grinding wheel, and the machining accuracy of the workpiece center hole. Fine grinding can achieve a size accuracy of 1 micron and a roundness of 0.5 microns. ④ Grinding: Using the principle of mutual grinding of mating parts to select and process irregular protrusions on the machined surface. The diameter of abrasive grains, cutting force, and cutting heat can all be precisely controlled, making it the highest precision machining method in precision machining technology. The hydraulic or pneumatic fittings in the precision servo components of the aircraft, as well as the bearing parts of the dynamic pressure gyroscope motor, are all processed using this method to achieve an accuracy of 0.1 or even 0.01 microns and a micro roughness of 0.005 microns.