Ball screw device having tunnel raceway, and method for manufacturing the same

A method for manufacturing a ball screw device of a screw axis having a helical groove on its outer circumference for balls to circulate thereon, and a nut having a helical groove on its inner circumference for balls to circulate thereon, and a number of balls circulating in an orbit along the helical groove of the screw axis and the opposing helical groove of the nut, and a tunnel raceway (for the balls to circulate unlimitedly) characterized in having a through-hole cut within the wall of the nut for the balls to circulate from one end of the helical groove to the other end, with a guidepath formed on either end of the helical groove to feed the balls into the tunnel raceway, with a means provided between the helical groove on one end face of the nut and the helical groove on the screw axis to stop the balls from exiting either helical groove, with the means to prevent the balls from exiting either helical groove being a structure in which, based on the baseline of 180 degrees, as shown in the cross-sectional view of both helical grooves, one helical groove of the aforementioned screw axis is supported at two points, while the other helical groove of the aforementioned nut is supported at one point, characterized in that a helical cut-out groove is provided by inserting the first tool, such as a cutting tool or the like, into a cut-out formed on the end face of the nut, or into a hole larger in diameter than the balls circulating through the guidepath, with a through-hole being provided within the tunnel raceway from one end of the outer circumference of the nut to the other end, by inserting the second tool into the hole to make a clearance for the balls to circulate toward the end face of the nut, with the clearance being communicated with the helical cut-out groove.