Form tap and method of making such

A grinding tool for forming threads on a form tap, the grinding tool comprising:

• a grinding wheel, the grinding wheel having a peripheral surface;
• first and second ribs and a trough therebetween;
• the first and second ribs projecting radially from the peripheral surface of the grinding wheel for grinding the threads;
• the first rib being sized and shaped to grind roots of threads on a finishing portion of the form tap and comprising a first peak and defining:
• a first outer diameter;
• and
• a first rib width;
• the second rib being sized and shaped to grind roots of threads on a chamfer portion of the form tap and comprising a second peak and defining:
• a second outer diameter that is smaller than the first outer diameter;
• and
• a second rib width that is smaller than the first rib width;
• the trough having a grinding surface for grinding crests of the threads on both the finishing and chamfer portions of the form tap;
• and
• the first and second peaks being spaced apart by a peak spacing distance, the peak spacing distance being different than a pitch of the threads.

A method of forming the thread portion of a form tap using a unitary grinding tool, the method comprising:

• providing a blank, the blank having a first longitudinal axis defining a first axis of rotation, and an outer surface;
• rotating the blank about the first longitudinal axis;
• providing a grinding tool, the grinding tool defining a second axis of rotation and having a peripheral surface comprising first and second ribs projecting radially therefrom;
• rotating the grinding tool about the second axis of rotation, the second axis of rotation being substantially parallel to and offset from the first axis of rotation;
• positioning the first and second axes of rotation at a first distance so that at least one of the first and second ribs interfere with the outer surface of a chamfer portion of the blank
• imparting relative axial movement between the blank and the grinding tool at an axial feed rate and simultaneously increasing the distance between the first and second axes of rotation, thereby at least partially forming a plurality of threads on the chamfer portion, the threads having crests spaced at a constant crest-to-crest spacing;
• and
• maintaining the relative axial motion between the blank and the grinding tool at the axial feed rate while maintaining the second axis of rotation at a second distance from the first axis thereby at least partially forming a plurality of threads on a finishing portion of the form tap, the threads on the finishing portion being continuous with, and having a constant crest-to-crest spacing with the threads on the chamfer portion.