From the perspective of the machining operation process, CNC machining can be divided into three main stages: programming, tool setting, and automatic machining. Among them, programming and tool setting are preparatory tasks. Whether the program is written correctly, the cutting parameters are chosen reasonably, and the tool-setting parameters are entered accurately will all be reflected in the actual machining process.
Therefore, to ensure the accuracy of CNC machining operations, trial machining is usually carried out to verify whether there are any issues in automatic machining. During trial machining, strictly following the “Three Checks, Two Musts, and One Pause” principle can greatly reduce the risk of collisions during machine operation.
1. Three Checks
① Check the program
All CNC operations are executed through program commands. By reviewing the program statements and program name, potential issues can be identified and corrected promptly. To avoid repeated or missed checks, follow a fixed sequence:
- First, check the program name. Since CNC operations require a large number of program commands, many program files are stored in the system. When calling up the program name in automatic mode, pay special attention to the file suffix and program format.
- Next, check the program segments. Use simulation software to verify whether specific program statements contain errors. If there are logical inconsistencies in the code, the software will automatically highlight them, allowing the programmer to make corrections until the program runs without issues.
② Check the workpiece coordinates
The screen will display detailed information such as the machine coordinates and workpiece coordinates for the current tool. Compare the displayed values with the actual position of the tool tip to ensure they match. Due to factors such as fixtures or tool wear, some coordinate deviation may occur. If the deviation exceeds the tolerance, it may disrupt machining progress and cause collisions. Cross-checking the coordinates can effectively prevent this.
③ Check the tool tip position
Since CNC machining and cutting are performed by the tool, the tool tip position must be carefully inspected. After prolonged use, the tool tip will wear. Without affecting machining quality, operators should regularly adjust tool positions to prevent collisions with the workpiece or chuck. Also, compare the actual tool tip position with the screen display; if there is a large discrepancy, stop machining, retract the tool after the machine halts, and reinstall/adjust it.
2. Two Musts
① Must use single-block execution
CNC machines have a Single Block (SBL) execution function. When enabled, the machine stops after completing each block of code, requiring the operator to manually start the next block. This allows ample time for checking the tool, coordinates, and program before proceeding, greatly reducing collision risks. Although it may slow down production, it significantly improves quality and safety.
② Must use low feed rate
By adjusting the feed rate override knob, you can reduce the tool’s cutting speed. This gives you time to verify whether the tool tip position matches the displayed coordinates before it starts cutting. If they don’t match, you can stop the machine in time to prevent a crash. This is especially important in internal hole machining, where incorrect entry or withdrawal can lead to dimensional errors, tool breakage, or collisions. Using a low feed rate helps prevent such problems.
3. One Pause
Strictly speaking, you should pause multiple times during automatic machining. Pausing gives the operator time to mentally prepare and observe the tool tip position versus the coordinate display. In particular, if chips become wrapped around the workpiece or tool, pressing the cycle stop button allows time to resolve the issue without rushing, reducing the risk of operational errors.
If you want, I can also reformat this into a concise training guide for CNC operators so it’s easier to follow on the shop floor. That way it becomes a quick-reference checklist rather than a long article. Would you like me to do that?
