CNC lathe collisions are usually caused by the following reasons:

1. Program error: When writing a machining program for a CNC lathe, if the coordinates or trajectory calculations are wrong, the tool may collide with the workpiece or fixture. This may be caused by a logical error or input error when the programmer writes the code.

2. Incorrect tool selection: If the tool size selected for a CNC lathe is inappropriate or the tool is too long, it may cause collisions during machining. This may be caused by improper tool selection or incorrect machining parameter settings.

3. Clamping failure: If the workpiece is not clamped firmly or the fixture design is unreasonable, the workpiece may move or rotate during machining, and then collide with the tool.

4. Damage to machine tool parts: If the mechanical parts, transmission device or control system of the CNC lathe fails or is damaged, the CNC lathe tool position may be offset or unstable, causing a collision.

5. Incorrect machining parameter settings: If the machining parameters of the CNC lathe are not set correctly, such as the cutting speed, feed speed, cutting depth, etc. are set too large or too small, it may cause excessive cutting force or unstable cutting process during cutting, causing collision.

6. Workpiece design problems: If the workpiece design of the CNC lathe is unreasonable or complex shape processing is required during the machining process, the risk of collision may increase.

7. Operator error: If the operator of the CNC lathe operates improperly or is not skilled enough, it may cause the CNC lathe to collide. For example, misoperating the control panel or ignoring the alarm signal.

In summary, the collision of the CNC lathe may be caused by program errors, incorrect tool selection, clamping failure, damage to machine tool parts, incorrect machining parameter settings, workpiece design problems or operator errors. In order to avoid collisions, it is necessary to correctly write the machining program, select the appropriate tool, ensure stable clamping, keep the machine tool in good condition, correctly set the machining parameters, reasonably design the workpiece and train the operator.