Factors for Selecting Fixtures and Cutting Tools for CNC Lathes

Jigs and cutting tools are critical components in CNC machining; the appropriateness of their selection directly affects machining efficiency and quality. Jig selection must ensure sufficient accuracy, rigidity, and reliable positioning references, while tool selection typically takes into account the lathe’s machining capabilities, the nature of the machining operations, and the workpiece material, among other factors. When selecting jigs and cutting tools, it is essential to first understand the specific characteristics of each type and then choose accordingly based on the particular application.
1. Workpiece Clamping and Positioning
Workpiece positioning is the first step in any machining operation, and it directly affects both machining accuracy and efficiency. When positioning a workpiece, the primary task is to select appropriate datum surfaces—since these datums have a direct impact on the dimensions and accuracy of the machined features. There are two main types of datums: rough datums and finish datums, and it is essential to ensure consistency among the design datum, process datum, measurement datum, and programming origin. When developing a clamping scheme, the number of clamping operations should be minimized as much as possible. The selection of CNC turning fixtures is a critical component of the clamping strategy. For rotational workpieces such as shafts, clamping can be achieved using a four-jaw independent chuck or a three-jaw self-centering chuck; for disc-shaped parts, adjustable jaw chucks or quick-adjustable chucks are effective choices. For applications with stringent requirements, in addition to selecting suitable chucks, it is often preferable to design dedicated tooling to assist the machining process, or to leave an allowance for subsequent grinding on a surface grinder.
2. Selection of Turning Tools and Determination of Cutting Parameters
CNC cutting tools are the primary components in turning operations. When selecting tools, it is essential to comprehensively consider the compatibility among the workpiece, the CNC machine tool, and the cutting tool itself. Whenever possible, larger-diameter tools should be chosen, as this can extend tool life and enhance production efficiency. Furthermore, CNC machine tools impose specific material requirements on turning tools; these requirements encompass not only the tool’s hardness, thermal conductivity, and strength but also its cost-effectiveness in machining applications.
The tool geometry should be determined based on the contour drawing of the workpiece and its dimensional accuracy requirements; moreover, larger-diameter tools or form tools should be selected to improve turning efficiency and extend tool life.
It is also important to properly control the cutting parameters. This requires careful attention to the operating parameters of each machining operation, which in turn influences the CNC programming data. During CNC programming, the cutting parameters must be accurately determined so that the depth of cut (back engagement), cutting speed (spindle speed), and feed rate (feed per revolution) are properly coordinated, thereby enhancing the efficiency of CNC turning and achieving the desired surface finish.