Although we can determine the coordinate of the tool reference point by returning to the reference point, or determine the coordinate of the workpiece and machine tool by measurement, the workpiece coordinate system is independent of the machine tool coordinate system after it is established. They are still independent of each other.
The CNC system does not know the position of the workpiece in the machine tool, nor does it know the position of the tool tip in the machine tool, nor can it determine their relative positions. Therefore, it is necessary to use trial cutting method for tool setting.
The trial cutting method requires manually returning the machine tool to the reference point, clamping the workpiece blank 1 on the chuck, and measuring D (workpiece diameter) and L (distance that the workpiece extends from the three-jaw chuck). Start the machine tool and manually adjust the tool (taking the 90-degree outer circle turning tool as an example).
1. Gently touch the end face of the rod with the tool tip, then move in the Z direction and withdraw the tool in the X direction, recording the CRT dynamic coordinate value Z;
2. Gently touch the outer circle of the rod with the tool tip, adjust the tool, then move in the X direction and withdraw the tool in the Z direction, recording the CRT dynamic coordinate value X;
3. Calculate the tool offset value (L1, L2). The value of L1 and L2 can be substituted into the formula for calculation.
4. The tool offset value (L1, L2) of the CNC lathe is input into the CNC system. After the tool offset value is input into the CNC system, the tool path will be automatically corrected. The trial cutting method can also be used for multi-tool processing. The tool setting process for other tools is the same. The tool offset value of each tool is input into the corresponding tool offset register for compensation in the CNC system. The deviation value of other tools relative to the first tool position can also be used as the compensation value.
The above tool setting method is essentially to make the tool tip of each tool contact with the intersection of the workpiece outer circle generatrix and end face, and calculate the tool deviation of each tool based on this intersection point.
The accurate tool setting method when using the trial cutting method is to rotate the workpiece sample end face and outer circle once while manually adjusting the tool, and carefully measure the length L of the sample extending from the chuck and the diameter D of the trial cutting outer circle. Lower the feed rate to make the contact degree between each tool and the workpiece as uniform as possible, which can effectively improve the cutting and setting accuracy. The advantage of using trial cutting method for tool setting is that no special tool setting tool is required. The operator only needs to follow the normal operation, which is simple, fast, correct, and effective.
For CNC lathes with multiple tools, there is also a positional deviation between each tool. If the tool offset value is determined one by one using the trial cutting method, the accuracy will inevitably decrease, and the efficiency will be low and time-consuming.
When automatic tool setting device is used for tool setting, the standard tool is set by the trial cutting method. The tool offset value of other tools relative to the standard tool is obtained by the sensor of the tool setting device, and calculated by the CNC system to determine the tool offset value of each tool relative to the workpiece.
The difference between the automatic tool setting device and the manual tool setting method lies in that it can automatically capture information, calculate the tool offset value, and store the tool offset value.
Simply put, the tool setting principle of the automatic tool setting device of CNC lathe is to determine the position of different tools in the tool setting device, calculate the position offset value (tool offset value) by the CNC system, and store the tool offset value.