Abstract: This paper introduces the function, principle, and usage of tool tip compensation. Taking the machining program of a wheel flange tread as an example, it illustrates the specific application of the tool radius compensation function. Keywords: Tool radius compensation; wheel flange tread; cutting program; FANUC CNC system 1 Introduction In actual machining, due to the roundness of the tool tip, the tool center trajectory cannot coincide with the contour of the workpiece. Instead, it should be offset from the workpiece contour by a radius value R. This offset is called tool radius compensation. Most CNC devices have a tool radius compensation function, which facilitates program compilation. When compiling a part machining program, it is not necessary to calculate the tool center trajectory; programming is only required based on the part contour. Using the tool radius compensation command and manually inputting the tool radius on the control panel, the CNC device can automatically calculate the tool center trajectory and move according to it. That is, after executing tool radius compensation, the tool automatically deviates from the workpiece contour by a tool radius value, thereby machining the required workpiece contour. 2. Preparations for Implementing Tool Tip Radius Compensation Before machining the workpiece, the relevant data for tool tip radius compensation must be input into the memory so that the CNC system can automatically compensate for the error caused by the tool tip radius. 1) Tool Radius: The shape of the workpiece is directly related to the size of the tool tip radius; therefore, the tool tip radius must be input into the memory. 2) Tool Shape and Position Parameters: The shape of the cutting tool determines the position of the tool's radius; therefore, parameters representing the tool's shape and position must also be input into the memory. These tool shape and position parameters are called the tool tip orientation (Tr), represented by 0 to 9 respectively. 3. Tool Radius Compensation Process Tool compensation includes three stages: tool compensation establishment, tool compensation execution, and tool compensation cancellation. Tool compensation establishment is the process where, as the tool approaches the workpiece from its starting point, the tool center transitions from coinciding with the programmed trajectory to deviating from the programmed trajectory by an offset amount. Program segments containing G41 or G42 are the program segments that establish tool compensation. G41 is for left tool radius compensation, and G42 is for right tool radius compensation. After the G41 and CA2 program segments, the tool center is always offset from the programmed trajectory by an offset amount until the tool compensation is canceled. The program segment containing G40 is the program segment that cancels the tool compensation; it is the process where the tool leaves the workpiece, and the tool center trajectory then overlaps with the programmed trajectory. Both tool compensation establishment and cancellation should be performed in a non-cutting state, and G40 must be used in pairs with G41 or G42. 4. Using the tool radius compensation function of the FANOU system to realize the machining of wheel flange treads Currently, we have carried out CNC retrofitting on two wheel lathes. The CNC system selected is the FANOUCO-TD system: The contour of the wheel flange tread is composed of several arcs and oblique lines that are tangent or intersecting. The task of contour calculation is to calculate the center of these arcs and the start and end points of the oblique lines and arcs. The tool tip is circular: if the trajectory of the tool center is to be calculated, the workload is very large. The following example, using the locomotive and coal/turbine wheel flange tread profile (TB449-76), illustrates the specific application of the tool radius compensation function. A Sandvik tool with a radius R of 3.333 and a tool width of 55mm is selected. Machining begins with the wheel chamfer. A machining program is executed to process a wheel with a width of 140mm. 1) Before program execution, the tool compensation value is input into the memory, as displayed on the CRT. 2) The cutting program for the profile tread profile: This program starts by machining the wheel chamfer, quickly positioning the tool at point V; adding tool radius compensation; changing the tool; encountering the tool, completing one machining cycle. 5. Conclusion The two modified wheel lathes exhibit reliable performance and stable operation during use. Machining accuracy has been improved, and the price is far lower than purchasing a new machine tool.