1. The provision of dimensional data on part drawings should comply with the principle of convenient programming

(1)The dimension annotation method on the part drawing should be adapted to the characteristics of CNC machining
On the CNC machining part drawing, the same reference should be used to indicate dimensions or coordinate dimensions should be provided directly. This annotation method is not only convenient for programming, but also facilitates the coordination between dimensions, bringing great convenience in maintaining consistency between design standards, process standards, detection standards, and programming origin settings. Due to the fact that part designers generally consider assembly and other usage characteristics more in dimension annotation, they have to adopt a partially scattered annotation method, which will bring many inconveniences to process arrangement and CNC machining. Due to the high precision of CNC machining and repetitive positioning, it will not damage the usage characteristics due to the generation of large accumulated errors. Therefore, the local scattered annotation method can be changed to the annotation method with the same reference dimension or directly providing coordinate dimensions.

(2)The conditions for the geometric elements that constitute the contour of the part should be sufficient

When manually programming, calculate the coordinates of the base point or node. When automatic programming, it is necessary to define all geometric elements that make up the contour of the part. Therefore, when analyzing part drawings, it is necessary to analyze whether the given conditions of geometric elements are sufficient. Like arcs and straight lines, arcs and arcs are tangent on the drawing, but according to the dimensions given on the drawing, when calculating the tangent conditions, they become intersecting or apart. Due to insufficient geometric element conditions that make up the parts, programming cannot be started. When encountering this situation, it should be resolved through consultation with the part designer.

2. The structural craftsmanship of each processing part of the part should comply with the characteristics of CNC machining

(1)It is best to use a unified geometric type and size for the inner cavity and outer shape of the parts. This can reduce tool specifications and tool changes, making programming convenient and improving production efficiency.

(2)The size of the inner groove fillet determines the size of the tool diameter, therefore the inner groove fillet radius should not be too small. The quality of part craftsmanship is related to the height of the processed contour and the size of the transition arc radius.

(3)When milling the bottom plane of the part, the radius r of the groove bottom fillet should not be too large.

(4)Unified benchmark positioning should be adopted. In CNC machining, if there is no unified benchmark positioning, the reinstallation of the workpiece may lead to the mismatch of contour positions and dimensions on the two machined surfaces. Therefore, to avoid the above-mentioned problems and ensure the accuracy of their relative positions after two clamping processes, a unified benchmark positioning should be used.
It is best to have suitable holes on the parts as positioning reference holes. If not, process holes should be set as positioning reference holes, such as adding process lugs on the blank or setting process holes on the remaining amount to be milled in subsequent processes. If it is not possible to produce process holes, at the very least, a precision machined surface should be used as a unified reference to reduce the error caused by two clamping operations. In addition, it is necessary to analyze whether the required machining accuracy, dimensional tolerances, etc. of the parts can be guaranteed, and whether there are any unnecessary dimensions that cause conflicts or closed dimensions that affect the process arrangement.