Introduction to NC lathe programming

一、 Provisions on coordinate system and moving direction of lathe

1. It is always assumed that the workpiece is stationary and the tool moves relative to the workpiece.

2. The coordinate system is a right-hand Cartesian coordinate system. As shown in the figure, the direction of the thumb is the positive direction of the X axis, the index finger is the positive direction of the Y axis, and the middle finger is the positive direction of the Z axis. On the basis of determining the X, y and Z coordinates, the directions of the three rotational coordinates a, B and C can be easily determined according to the right-hand spiral rule.

3. The movement of the specified Z coordinate is determined by the spindle that transmits the cutting power. The coordinate axis parallel to the spindle axis is the Z axis. The X axis is horizontal, parallel to the workpiece clamping surface and perpendicular to the Z axis.

4. It is specified that the direction of the tool away from the workpiece is the positive direction of the coordinate axis.

When the lathe is a front tool rest, the X axis is forward and points to the operator. When the lathe is a rear tool rest, the X axis is forward and backward, away from the operator.

二、 Lathe coordinate system

The lathe coordinate system is a zox axis Cartesian coordinate system established with the lathe origin as the origin of the coordinate system.

1. Machine zero

The origin of the machine tool (also known as the mechanical origin), that is, the origin of the lathe coordinate system, is a fixed point on the lathe. Its position is determined by the lathe design and manufacturing unit. Generally, users are not allowed to change it.

2. Lathe reference point

The reference point of the lathe is also a fixed point on the lathe, which is the limit position for limiting the movement of the tool rest with mechanical stops or electrical devices. The function of the lathe reference point is to position the lathe coordinate system. Because the system will set the current position to (0, 0) no matter where the tool rest stays after each start-up, which will cause inconsistency of the reference. After the CNC lathe is started, it is first necessary to return to the reference point (also known as zero point). After the lathe is powered on and before returning to the reference point, no matter where the tool rest is, the coordinate values of Z and X displayed on the CRT are all 0. Only after returning to the reference point is completed, the tool rest moves to the lathe reference point. At this time, the CRT displays the coordinate value of the tool rest reference point in the lathe coordinate system, that is, the lathe coordinate system is established.

三、 Workpiece coordinate system

When machining on a CNC lathe, the workpiece can be clamped at any position under the lathe coordinate system by a chuck. This makes programming in the lathe coordinate system very inconvenient. Therefore, when programmers write part processing programs, they usually choose a workpiece coordinate system, also known as the programming coordinate system. The coordinate values in the program are based on the workpiece coordinate system.

The origin of the workpiece coordinate system can be determined by the programmer according to the specific situation, and is generally set at the design benchmark or process benchmark of the drawing. According to the characteristics of CNC lathe, the origin of workpiece coordinate system is usually set at the center of left and right end faces of workpiece or the center of chuck front end face.

Post time: Sep-09-2022