Linear motion apparatus and method for manufacturing thereof

A linear motion apparatus comprising:

• a guide shaft including a spiral-shaped or linear-shaped rolling element rolling groove;
• a movable body including a spiral-shaped or linear-shaped rolling element rolling groove opposed to the rolling element rolling groove of the guide shaft;
• a large number of rolling elements rollably moving along a rolling element rolling passage formed between the rolling element rolling grooves of the guide shaft and movable body;
• and,
• a rolling element return passage communicating with the rolling element rolling passage,
• wherein, in the portion of the rolling element rolling groove of the movable body that is adjacent to an open end of a rolling element return passage, an escape portion is formed by abrasive flow machining in such a manner that the grinding depth thereof increases gradually toward the open end of the rolling element return passage, and that the escape portion is formed in a crowning shape which expands toward the open end of the rolling element return passage, and which comprises a curved surface a curvature of which is continuously changed.