Movement No. 99 demonstrates a spiral guide mechanism mounted on the face of a rotating disk, used to produce a controlled radial feed motion. A spiral groove or guide is cut into or attached to the face of the disk. As the disk rotates, a follower pin or block riding in the spiral groove is progressively moved either inward toward the center or outward away from it, depending on the direction of rotation. This converts continuous rotary motion into a slow, steady radial linear advance. The mechanism was notably used in drilling machines to provide the feed motion — gradually advancing the cutting tool into the workpiece at a controlled and consistent rate with each revolution of the disk. Its simplicity and smooth feed characteristics made it a practical solution in early machine tool design.
99. Spiral guide attached to the face of a disk; used for the feed-motion of a drilling machine.