The reasons why the vertical machining center machine tool column is not tight may be as follows:

1. Material or processing problems: If the vertical machining center's column material is of poor quality or there are processing problems, such as cracks, looseness, etc., the column may not be tight.

2. Loose parts: After the vertical machining center has been used for a period of time, the screws, nuts or other fixed parts connecting the columns may become loose, causing the columns to become loose.

3. Insufficient lubrication: If the sliding surface of the vertical machining center or the sliding parts of the vertical machining center are not lubricated enough, it may lead to increased friction, which may cause the column to become loose.

4. Aging of machine tools: If the vertical machining center is used for too long, the parts of the column may be worn, which may cause the column to become loose.

5. Design defects: Improper design of the vertical machining center column, or poor quality of parts used, may cause the column to be loose.

6. Improper operation: If the operator of the vertical machining center uses the machine tool improperly, such as overload use, overspeed operation, etc., the column may not be tight.

In order to solve the problem of the vertical machining center column not being tight, the following measures can be taken:

1. Regularly check the connecting screws, nuts and other parts of the vertical machining center column to ensure their tightness.

2. Carry out lubrication and maintenance on the vertical machining center regularly to ensure that the sliding surface and sliding parts of the vertical machining center column are fully lubricated.

3. Before each use of the vertical machining center, a comprehensive inspection must be carried out to ensure the normal working condition of each component of the vertical machining center.

4. If you find that the column is not tight, adjust or repair it in time to avoid further damage to the vertical machining center machine tool.