There can be many reasons for thread damage on a CNC lathe, here are some common reasons:

1. Improper tool selection: The CNC lathe selects inappropriate tools or the tools are severely worn, resulting in uneven cutting force or excessive cutting, thus damaging the thread surface.

2. Improper setting of cutting parameters: Improper setting of cutting speed, feed rate, cutting depth and other cutting parameters of CNC lathe, resulting in excessive cutting force during the cutting process, thus damaging the thread surface.

3. Processing program errors: There are errors in the written CNC machining program, resulting in incorrect tool paths or improper setting of cutting parameters, causing damage to the thread surface.

4. Improper workpiece clamping: CNC lathe workpiece clamping is not firm or the fixture design is unreasonable, causing the workpiece to vibrate or shift during processing, resulting in inaccurate thread processing or damage.

5. CNC system failure: CNC system failure or program execution error leads to incorrect tool paths or out-of-control cutting parameters, causing thread surface damage.

6. Tool wear: CNC lathes use severely worn tools for processing, resulting in greater cutting force and heat during the cutting process, thus damaging the thread surface.

7. Material quality issues: The quality of materials processed by CNC lathes is poor or contains hard inclusions, which makes cutting difficult or causes abnormalities during the cutting process, causing damage to the thread surface.

8. Improper operator skills: CNC lathe operators lack experience or have low technical level, resulting in improper operation during processing and damage to the thread surface.

Considering the above factors, reasonable selection of cutting parameters, tools and clamping methods for CNC lathes, and strengthening of maintenance and operation training for CNC lathes can effectively prevent and reduce the occurrence of thread damage on CNC lathes.