What are the main causes of machining errors?

The machining error reflects the machining accuracy. The main reasons for machining errors are as follows:
Machine tool manufacturing error
Machine tool manufacturing errors mainly include spindle rotation error, guide rail error and transmission chain error. Spindle rotation error refers to the change of the actual spindle rotation axis relative to its average rotation axis at each moment, which will directly affect the precision of the workpiece.
The main reasons for the spindle rotation error are the coaxiality error of the spindle, the error of the bearing itself, and the coaxiality error between the bearing and the spindle winding. The guide rail is the reference point for determining the relative position of various machine tool parts on the machine tool, and also the reference point for machine tool movement. The manufacturing error of the guide rail itself, uneven wear of the guide rail and installation quality are important factors causing the guide rail error. Transmission chain error refers to the relative motion error between transmission elements at both ends of the transmission chain. It is caused by the manufacturing and assembly errors of various parts of the drive chain and the wear during use.
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Geometric error of tool
Any tool will inevitably wear in the cutting process, resulting in changes in the size and shape of the workpiece. The influence of tool geometric error on machining error varies with the type of tool: when using a fixed size tool, the tool manufacturing error will directly affect the machining accuracy of the workpiece; For general tools (such as turning tools), manufacturing errors have no direct impact on machining errors.
Geometric error of fixture
The function of accessories is to make the workpiece have the correct position equivalent to the cutter and machine tool, so the geometric error of accessories has a great influence on the machining error (especially the position error).
positioning error
The positioning error mainly includes the datum misalignment error and the manufacturing error of the positioning pair. When machining a workpiece on a machine tool, select several geometric elements on the workpiece as the positioning reference points during machining. If the selected positioning reference point does not match the design reference point (the reference point used to determine the size and position of a surface on the drawing part), datum misalignment error will occur.
The positioning surface of the workpiece and the positioning element of the fixture together constitute a positioning pair. The large position change of the workpiece caused by the inaccurate manufacturing of the positioning torque and the coincidence of the clearance between the positioning pairs is called the inaccurate manufacturing error of the positioning torque. The manufacturing error caused by inaccurate positioning torque will only occur when using the adjustment method, and will not occur in the trial cutting method.
Error caused by force deformation of machining process system
Workpiece stiffness:
In the machining system, if the rigidity of the workpiece is relatively low compared with that of the machine tool, tools and accessories, the deformation of the workpiece due to insufficient rigidity under the action of the cutting force will have a greater impact on the machining error.
Tool stiffness:
The rigidity of the cylindrical turning tool in the normal (y) direction of the machined surface is very large, and its deformation can be ignored. When drilling small diameter inner holes, the rigidity of the cutter bar is very poor, and the force and deformation of the cutter bar have a great impact on the hole processing accuracy.
Rigidity of machine tool parts:
Machine tool components consist of many parts. So far, there is no simple method for calculating the stiffness of machine tools. At present, experimental methods are mainly used to determine the stiffness of machine tool components. The factors affecting the rigidity of machine tool components include the influence of gasket surface contact deformation, friction, low rigidity parts and clearance.
Error caused by thermal deformation of machining process system
The thermal deformation of the process system has a great influence on the machining error, especially in precision machining and machining of large parts, the machining error caused by thermal deformation sometimes accounts for 50% of the total error of the workpiece.
Setting error
In each processing process, the process system shall be adjusted in one way or another. Adjustment errors occur because the adjustment is not accurate. In the process system, the mutual position accuracy of workpiece and cutter in the machine tool is guaranteed by adjusting the machine tool, cutter, accessory or workpiece. When the original accuracy of the machine tool, cutter, accessory and blank meets the process requirements without considering dynamic factors, the adjustment error plays a decisive role in the processing error.
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measurement error
When measuring parts during or after processing, the measurement accuracy is directly affected by the measurement method, the accuracy of measuring tools, the workpiece and subjective and objective factors.
internal stress
The stress that is not affected by external force but exists inside the part is called internal stress. Once the workpiece generates internal stress, the metal of the workpiece will be in a high-energy unstable state, instinctively changing to a low-energy stable state, accompanied by deformation, so that the workpiece will lose its original processing accuracy.
The above introduces several errors in machining, and I hope the above introduction can help you!