The Nine Major Errors Commonly Occurring in Machining
2026-03-11
Manufacturing errors in machine tools primarily include spindle rotational error, guideway error, and drive-train error. Spindle rotational error refers to the deviation of the spindle’s instantaneous axis of rotation from its mean axis of rotation, and it directly affects the dimensional accuracy of the workpiece being machined.
The magnitude of machining errors reflects the level of machining accuracy. The primary causes of machining errors in mechanical processing are as follows. We hope this will be helpful to all engineering professionals!
1. Manufacturing errors of machine tools
Manufacturing errors in machine tools primarily include spindle rotational error, guideway error, and drive-train error. Spindle rotational error refers to the deviation of the spindle’s instantaneous axis of rotation from its mean axis of rotation, and it directly affects the dimensional accuracy of the workpiece being machined.
The primary causes of spindle rotational error include spindle coaxiality error, bearing manufacturing errors, coaxiality errors between bearings, and spindle deflection. Guideways serve as the reference for determining the relative positional relationships among machine tool components and also as the reference for machine tool motion. Manufacturing errors in the guideways themselves, non-uniform wear of the guideways, and installation quality are major factors contributing to guideway errors. Transmission chain error refers to the error in the relative motion between the driving and driven elements at the two ends of the transmission chain. It arises from manufacturing and assembly errors in each link of the transmission chain, as well as from wear during operation.
2. Geometric errors of cutting tools
During the cutting process, all cutting tools inevitably experience wear, which in turn leads to changes in the dimensions and geometry of the workpiece. The influence of tool geometric errors on machining errors varies depending on the type of tool: when using fixed-size tools, manufacturing errors of the tool directly affect the machining accuracy of the workpiece; however, for general-purpose tools (such as turning tools), their manufacturing errors have no direct impact on machining errors.
3. Geometric Errors of the Fixture
The function of a fixture is to ensure that the workpiece is properly positioned relative to the cutting tool and the machine tool; therefore, geometric errors in the fixture have a significant impact on machining errors, particularly positional errors.
4. Positioning Error
Positioning errors mainly include datum mismatch error and manufacturing inaccuracies of the positioning elements. When machining a workpiece on a machine tool, several geometric features on the workpiece must be selected as the positioning datums for the machining operation. If the selected positioning datum does not coincide with the design datum (the datum used on the part drawing to define the dimensions and location of a particular surface), a datum mismatch error will arise.
The workpiece locating surface and the fixture locating elements together form a locating pair. The greater variation in the workpiece’s position caused by inaccuracies in the fabrication of the locating pair and by clearance between the mating surfaces of the locating pair is referred to as locating-pair manufacturing inaccuracy error. This error occurs only when the adjustment method is used for machining; it does not arise in trial-cutting machining.
5. Errors caused by deformation of the process system under load
Workpiece stiffness:
In a machining system, if the workpiece exhibits relatively low stiffness compared with the machine tool, cutting tool, and fixture, the deformation of the workpiece caused by insufficient stiffness under the action of cutting forces will have a significant impact on machining errors.
Tool rigidity:
External turning tools exhibit very high stiffness in the surface normal (y) direction, such that their deformation can be neglected. In contrast, when boring small-diameter internal holes, the tool shank has poor stiffness, and any deflection of the shank under load can significantly affect hole-machining accuracy.
Machine tool component stiffness:
Machine tool components are composed of numerous parts, yet to date there remains no suitable simplified analytical method for determining their stiffness; currently, experimental methods are still the primary means of measuring such stiffness. The factors that influence the stiffness of machine tool components include the effects of contact deformation at mating surfaces, frictional forces, low-stiffness components, and clearances.
6. Errors Caused by Thermal Deformation of the Process System
Thermal deformation of the machining system has a significant impact on machining errors, particularly in precision and large-part machining, where thermal-induced errors can account for up to 50% of the total workpiece error.
7. Adjust the error
In every operation of machining, some form of adjustment to the process system is invariably required. Because such adjustments can never be perfectly accurate, adjustment errors inevitably arise. Within the process system, the positional accuracy between the workpiece and the cutting tool on the machine tool is ensured through adjustments to the machine tool, the cutting tool, the fixture, or the workpiece itself. When the inherent accuracies of the machine tool, cutting tool, fixture, and workpiece blank all meet the process requirements—and dynamic factors are disregarded—adjustment errors become the decisive factor in determining overall machining errors.
8. Measurement Error
During machining or post-machining measurement, the measurement accuracy is directly influenced by the measurement method, the precision of the measuring instruments, and both objective and subjective factors related to the workpiece.
9. Residual Stress
Stress that exists within a component in the absence of external forces is referred to as residual stress. Once residual stress develops in a workpiece, the metal is driven into a high-energy, unstable state; it naturally tends to transform toward a lower-energy, stable state, accompanied by deformation, thereby causing the workpiece to lose its original machining accuracy.
Keywords:
Machine tool,Spindle,Workpiece
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