I think what Bluesman is getting at is that the material is not passing the tool in a direction perpendicular to the top face of the tool. I haven't looked at his .doc attachment because I can't open it. There is a sideways component to the motion due to the tool advancing along the work. This means that the chip does not come out parallel to the centerline of the tool it tends toward the side and runs into the thread flank on the trailing side. Leaning the tool into the thread at the helix angle means the chip comes out centered and the cut is more symmetric. |