What causes the arc dimensions in CNC lathe machining to be out of tolerance?
Release Date:
2026/03/20
Inadequate machining of arc dimensions is typically caused by a mismatch between the actual tool path and the programmed tool path during CNC turning. The primary contributing factors include tool compensation settings, machining parameters, machine tool condition, and process planning.
Main cause analysis:
Tool tip radius compensation is not enabled or is incorrectly configured.
When machining arcs on a CNC lathe, failure to use the G41 (left compensation) or G42 (right compensation) command for tool-tip arc-radius compensation will result in the actual machined arc radius being smaller than intended for external convex arcs or larger than intended for internal concave arcs.
For example: if the theoretical arc radius is R10 and the tool-tip arc radius is R0.4, the actual machined external convex arc radius without compensation will be approximately R9.6.
Meanwhile, an incorrect setting of the tool’s virtual tip position code (T value) can also result in improper compensation direction, leading to overcutting or undercutting.
Unreasonable cutting parameter settings
An excessively high feed rate F results in an inadequate response from the servo system, leading to “lost steps,” which is particularly pronounced during circular interpolation.
Excessive cutting depth or mismatched spindle speed can cause vibration or tool deflection, thereby compromising dimensional accuracy.
Machine tool mechanical issues
Excessive lead screw backlash or guide rail wear can result in backlash during reverse motion, thereby compromising the accuracy of circular interpolation.
Wear or loosening of the synchronous belt affects transmission accuracy, leading to positional deviation.
Unstable machine tool installation and resonance can also lead to machining instability.
Programming or computational errors
Incorrect calculation of the start point, end point, or center coordinates of the circular arc.
The transition segments in the toolpath were overlooked, or the G02/G03 commands were used improperly.
The tool compensation (G40) was not properly canceled in the program, resulting in abnormal subsequent motion.
Cutting Tool and Workholding Factors
Failure to replace worn cutting tools in a timely manner results in changes to the actual nose radius, rendering the original compensation values ineffective.
The workpiece is not securely clamped and shifts under the action of cutting forces.
Inaccurate tool installation height (tool tip center height deviating from the workpiece axis) affects the arc shape.
Yancheng Zhiyang Lianke Precision Machinery Co., Ltd.
National Unified Business Inquiry Hotline
No. 1, Wei Si Road, Yandu High-tech Industrial Development Zone, Yancheng City, Jiangsu Province, China.
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