Centerless grinding through the application of a helical twist to axial grooves

A workpiece for grinding between two grinding wheels and a platform comprising:

• a body with an outer circumference having a first end and a second end separated by a length;
• a continuous helical slot comprising:
• a first axial slot at a first end extending a length towards the second end having a depth from the outer circumference, the first axial slot having a flat surface at the depth from the outer circumference, the flat surface connected to a first side and a second side;
• a helical jog having a surface at the depth having first helical jog side and a second helical jog side connected to the first side and the second side of the first axial slot, the helical jog extending a length towards the second end;
• and
• a second axial slot having a surface at the depth adjoined to a first side and a second side connected to the first helical jog side and the second helical jog side;
• wherein the continuous helical slot has an angular overlap around the outer circumference of the body measured between an imaginary line drawn from a first edge of the first side of the first axial slot at the first end with the flat surface to an edge of the second side of the second axial slot of the continuous helical slot, the imaginary line confined to the second side of the first axial slot, the surface of the helical jog, and first side of the second axial slot, covering a portion of the circumferential surface of the workpiece, such that during grinding between the two grinding wheels and the platform, the angular overlap ensures an unbroken, intact, outer circumference continuous tangential contact with the two grinding wheels and the platform as the workpiece is rotated on the platform.

A method of manufacturing a control sleeve for a variable cam timing phaser comprising the steps of:

• placing a workpiece on a platform, the workpiece comprising:
• a body with an outer circumference having a first end and a second end separated by a length;
• and a continuous helical groove extending from a first end to the second end along the entire length of the body a depth from the outer circumference, the helical groove having a surface the depth from the outer circumference connected to a first side and a second side;
• wherein the helical groove has an angular overlap along the entire length of the body and around the outer circumference of the body measured between an imaginary line drawn from a first edge of the first side at the first end to the second end and to a second edge of the first side at the second end, the imaginary line remaining confined within the continuous helical groove;
• feeding the workpiece between two rotary grinding wheels which rotate at the same rotational speed in different directions, but different tangential speeds;
• grinding the workpiece such that the angular overlap ensures continuous tangential contact with the two rotary grinding wheels as the workpiece is rotated.