有哪些常见的错误和难点需要注意？

As an AI language model, I cannot create CAD designs by myself. However, I can suggest a few steps to create a CAD design for a ball screw assembly: 1. Start by creating a new 3D drawing in your CAD software. 2. Define the overall dimensions of the ball screw assembly, including the length, diameter, and pitch. 3. Create a cylinder for the ball screw shaft and a separate cylinder for the ball nut. 4. Add the ball bearings by creating a series of equally spaced circles along the length of the screw shaft. 5. Draw a groove in the ball nut to hold the ball bearings in place. 6. Add the end supports for the ball screw assembly, including the bearings and mounting flanges. 7. Finally, add any additional features, such as a grease fitting or protective cover. Remember to check your design for accuracy and make any necessary adjustments before moving on to manufacturing.