Abstract: A rack shaft of the present invention includes: an effective rack tooth row formed by plastic deformation of a shaft member and having a plurality of rack teeth that mesh with a pinion; a ball screw portion having no rack tooth; an ineffective rack tooth that is formed between the effective rack tooth row and the ball screw portion and that does not mesh with the pinion; and a padding portion that extends from an end of the ball screw portion toward the ineffective rack tooth and that covers at least a part of the ineffective rack tooth.

Abstract: While feeding an upholstery member, a sewing needle is reciprocated to form needle receiving holes, and an upper thread is passed through each needle receiving hole, caused to cross a lower thread, and pulled out of the needle receiving hole. The sewing cycle is repeatedly performed to form a stitch, so that stitches form a stitch line in a surface sheet. A direction of a force, which is generated by applying tension to the lower thread and which acts to rotate thread ends of a pair of adjacent stitches in each needle receiving hole about a crossing part of the upper thread and the lower thread, is defined as a rotation direction. The sewing needle is rotated in a direction opposite to the rotation direction to incline a diagonal line of the quadrangular shape forming the cross section relative to the feeding direction of the upholstery member.

Abstract: A rack shaft of the present invention includes: an effective rack tooth row formed by plastic deformation of a shaft member and having a plurality of rack teeth that mesh with a pinion; a ball screw portion having no rack tooth; an ineffective rack tooth that is formed between the effective rack tooth row and the ball screw portion and that does not mesh with the pinion; and a padding portion that extends from an end of the ball screw portion toward the ineffective rack tooth and that covers at least a part of the ineffective rack tooth.

Abstract: While feeding an upholstery member, a sewing needle is reciprocated to form needle receiving holes, and an upper thread is passed through each needle receiving hole, caused to cross a lower thread, and pulled out of the needle receiving hole. The sewing cycle is repeatedly performed to form a stitch, so that stitches form a stitch line in a surface sheet. A direction of a force, which is generated by applying tension to the lower thread and which acts to rotate thread ends of a pair of adjacent stitches in each needle receiving hole about a crossing part of the upper thread and the lower thread, is defined as a rotation direction. The sewing needle is rotated in a direction opposite to the rotation direction to incline a diagonal line of the quadrangular shape forming the cross section relative to the feeding direction of the upholstery member.