When the tool post of the wheel hub processing CNC vertical lathe is not locked tightly, there may be the following reasons:

1. Clamping nut problem: The clamping nut of the tool holder may not be tightened properly, or the nut itself is damaged or worn, resulting in insufficient clamping force. Check the clamp nut to make sure it is properly tightened and not damaged.
2. Tool holder slider problem: The frictional relationship between the tool holder slider and the guide rail may cause the instability of the tool holder position. Worn, loose, or insufficient lubrication of the sliders can cause the tool holder to not lock tightly. Check the carriage slides and rails to ensure they are in good condition and properly lubricated.
3. Locking device failure: The tool holder locking device of the CNC vertical lathe may be faulty or invalid. Check the working condition of the locking device to make sure it is working properly. If faulty, the locking device may need to be repaired or replaced.
4. Machine tool structure problems: The rigidity and stability of the machine tool structure may affect the tool holder locking. If the machine tool structure is loose, material fatigue, guide rail misalignment and other problems exist, it may lead to the locking failure of the tool holder. The machine tool structure needs to be maintained and inspected to ensure its normal rigidity and stability.
5. Operation error: The operator may not operate or fix the tool holder locking device correctly, resulting in the tool holder not being locked tightly. Train and instruct operators to use the tool holder locking device correctly and ensure correct operation.

For the problem that the tool holder is not locked tightly, it is necessary to carefully check the above factors and take appropriate measures to repair and adjust. If the problem cannot be solved, it is recommended to contact the manufacturer or professional technicians of the CNC vertical lathe for further support and solutions. Take care to ensure that before performing any maintenance or repair operations, the machine tool is powered off and the relevant safety standards and operating procedures are followed.