The common problems and solutions in CNC machining are as follows:

1. Bullet knife: This is usually caused by insufficient strength, too long, or too small of the cutting tool. The solution is to follow the principle of using tools that can be large but not small, short but not long, choose tools with appropriate strength, and leave as much uniform cutting allowance as possible.

2. Inaccurate operation: Inaccurate manual operation by the operator may lead to machining errors. The solution is to conduct repeated checks to ensure that operations such as centering and aligning are performed at the same point and height, while improving the operator's proficiency.

3. Collision: This may be due to improper safety height settings, program errors, or operator manual errors. The solution is to ensure that the safety height is set above the workpiece, the program sheet is consistent with the actual program tool, and the operator strengthens the inspection during manual operation to ensure that the program is executed correctly in sequence.

4. Poor cutting effect: Unreasonable cutting parameters, sharp tool edges, poor chip removal, etc. can all lead to poor cutting effect. The solution is to adjust the cutting parameters reasonably, regularly check and replace the cutting tools, ensure that the clamping of the cutting tools is as short as possible, and the clearance of the blade should not be too long. At the same time, consider programming cutting methods such as sequential milling.

5. Blade breakage and wear: This is usually caused by factors such as excessive feed rate, insufficient clamping force, and insufficient tool rigidity. The solution is to slow down the feed rate, clamp the tool and workpiece, use a machine tool and tool holder with good rigidity, and use the shortest allowed tool to clamp the handle deeper. For worn cutting tools, grinding should be carried out in the initial stage.

The above are only some common problems and solutions. The problems encountered in CNC machining may vary depending on the specific situation and need to be adjusted and handled according to the actual situation.