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Conceptual Analysis Of Several “Points” In CNC Lathes

Concept analysis of CNC lathe:

1. Zero point of CNC lathe

The origin of the CNC lathe coordinate system is called the machine zero (X = 0, Y = 0, Z = 0). The zero point of the machine tool is a fixed point on the machine tool, which is determined by the manufacturer in advance. The machine tool zero point M is the starting point of the machine tool coordinate system zero point and other coordinate systems, such as the workpiece coordinate system, the programming coordinate system and the reference point (or reference point) in the machine tool. The origin O of the CNC lathe machine coordinate system (XOZ) is generally located at the end face of the chuck, or at a certain distance from the end face of the jaws, or the machine tool reference point.

The origin O of the CNC milling machine coordinate system (X YZO) is generally located at the machine tool reference point or the upper surface of the left corner of the machine table.

2. Machine tool reference point (reference point)

The machine tool reference point (R) is a point artificially defined by the machine tool manufacturer. The coordinate position relationship between the machine tool reference point (R) and the machine tool zero point (M) is fixed and stored in the corresponding machine tool data of the CNC system. It is not allowed to change. In special cases, the position of the limit switch of the machine tool reference point (R) can be changed to change its position; but at the same time, the geometric distance between the machine tool reference point (R) and the machine zero point (M) must be accurately measured and stored Only the corresponding machine tool data of the CNC system can guarantee that the originally designed machine tool coordinate system will not be destroyed. After the control system is started, all axes must return to the reference point once in order to calibrate the travel measuring system. Most machine tools can automatically return to the reference point. If the control system loses the existing coordinate value due to power failure, it can return to the reference point and reacquire the accurate position value.

The position of the reference point R is accurately predetermined on each axis with stops and limit switches. The coordinate of the reference point to the machine zero is a known number, and the reference point is mostly located at the edge of the machining area.

3. Workpiece zero point (programming zero point)

When the operator or programmer creates a part program, the coordinate system established with a fixed point on the workpiece as the zero point is called the workpiece coordinate system (or programming coordinate system). The zero point of this workpiece coordinate system is called the workpiece zero point (or programmed zero point) W. The principle of selecting the zero point of the workpiece is to make it easy to convert the dimensions in the workpiece drawing into coordinate values, and try to directly use the drawing size as the coordinate value. The measuring system can be conveniently checked, clamped, adjusted, easily oriented and positioned.
The workpiece zero point of the CNC lathe is on the main axis of the right or left edge of the contour of the finished part. The zero point of the workpiece of the milling machine selects an external angle of the workpiece. After the zero point of the workpiece is selected (often the distance relative to the reference point), it is input into the CNC device when the machine tool is started.

4. Program zero point

Sometimes, for the convenience of machining or programming, a program zero point is set outside the workpiece zero point, which is specially used for programming. Sometimes the workpiece zero is regarded as the program zero.

5. Tool reference point

The machine tool zero point M, workpiece zero point W, reference point R and tool reference point of the CNC lathe: tool installation point E and tool holder installation point N. The tool installation point E is set at a fixed position of the tool holder, and its existence makes it possible to measure the tool size outside the machine tool. The measured value is input into the tool data storage area of ​​the CNC system. The tool length is represented by positive coordinates or L coordinates, and the tool tip misalignment or tool nose radius is represented by X and R or Q coordinates. Corresponding to the tool installation point, there is a tool holder installation point N on the tool holder. When the tool or tool holder is installed in the tool holder (such as a turret tool holder), the tool installation point coincides with the tool holder installation point. The tool reference point is very important for tool installation. Before processing, the tool data (ie tool length L and radius R, etc.) must be input to the CNC device and stored. For turning tools, the length L and the lateral distance Q are measured. For milling cutters, length L and radius R are measured.

6. Tool setting point and tool changing point

After the installation method of the parts is determined, the workpiece coordinate system, tool setting point and tool changing point must be selected. Tool setting point refers to the starting point of tool movement relative to parts during CNC machining, usually set as the origin of the workpiece coordinate system. The tool setting point can be set on the workpiece, or it can be set on a certain position of the fixture that has a certain relationship with the positioning reference of the workpiece. The selection principle is as follows: make programming simple. The tool setting point is easy to align on the machine tool, and it is convenient to check during processing. The processing error caused is small.

The tool change point should be set when the tool change is needed during CNC machining. The tool change point should be set outside the parts and fixtures to avoid hitting the workpiece or fixtures during tool change.

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