# How to calculate the points and nodes of precision parts processing

When programming precision parts, you must first calculate the coordinates of the tool path points. According to the workpiece pattern, according to the determined processing path and the allowable programming error, the calculation of the data that the numerical control system needs to input is called the numerical calculation of numerical control processing.

1. The concept and calculation of the base point: The contour of the workpiece is usually composed of many different geometric elements, such as straight lines, arcs, quadratic curves and other curves. (The concept of base point and node must not be confused) The connection point of these different geometric elements constituting the contour of the workpiece is called the base point. The base point of the adjacent base point contour can be directly used as the starting point or end point of its motion trajectory. At present, general CNC machine tools have linear and arc interpolation functions. When calculating the base point, only the coordinates of the start or end point of the trajectory (line segment) in the selected coordinate system and the center coordinate value of the arc motion trajectory are calculated. Therefore, the calculation of the base point is more convenient, and manual calculation is often used.
2. The concept and calculation of nodes: When using CNC machine tools without non-circular interpolation function to process non-circular contour workpieces, when preparing precision parts for processing, it is usually necessary to use straight lines or circular arcs to approximate non-circular curves , Called fitting processing. The intersection or tangency of the fitted line segment is called a node.

When programming a non-circular curve with a straight line or a circular arc, the program segment should be divided according to the nodes. The larger the approximate interval of the approximate line segment, the smaller the number of tangent points, and the larger the corresponding approximate error. The difficulty of node fitting calculation and the number of workpieces are relatively large, and it should be completed by a computer. Sometimes, it can also be done by manual calculation, but it requires programmers to have high mathematical processing capabilities.