Opening a keyway on a CNC lathe machine typically involves the following steps:

1. Choose the right tool: The first step is to choose the appropriate tool for cutting the keyway. Typically, a form tool or broaching tool is used to cut keyways on a CNC lathe machine.
2. Program the machine: Next, the CNC lathe machine must be programmed to cut the keyway. The programming involves specifying the dimensions of the keyway, including its width, depth, and length, as well as the feed rate and spindle speed.
3. Mount the workpiece: The workpiece must be securely mounted in the lathe chuck or collet to prevent it from shifting during the cutting process.
4. Perform a test run: Before cutting the keyway, it is a good practice to perform a test run to ensure that the program is correct and that the tool is set up properly.
5. Cut the keyway: Once the machine is properly set up, the cutting process can begin. The CNC lathe machine will move the cutting tool along the length of the workpiece, cutting away material to create the keyway. The depth, width, and length of the keyway are controlled by the CNC program.
6. Finish the keyway: After the keyway has been cut, it may need to be deburred and cleaned up to ensure a smooth surface finish.

It is important to note that opening a keyway on a CNC lathe machine requires expertise and training. It is recommended to consult the machine manual and seek the guidance of an experienced machinist to ensure proper setup and operation of the machine.