Page 17 - Demo

15GENERAL DRILLING HANDBOOKBody Clearance Diameter - The diameter of the body clearance behind the lands (Figure 1.2.17).Figure 1.2.17body clearance diameterdrill diameterBack Taper - The reduction in diameter from the outer corners towards the shank. It is expressed by the ratio of the reduction in diameter and the length of measurement.Web Taper - The increase in web thickness from the point of the drill to the shank end of the flutes. It is expressed by the ratio of the increase in thickness and the length of measurement.Lead of Helix - The distance measured parallel to the drill axis between corresponding points on the leading edge of a land in one complete revolution of the land (Figure 1.2.18).Helix Angle - The acute angle between the tangent to the helical leading edge and a plane containing the axis and the point in question. This angle lies in a plane normal to the radius at the point on the edge (Figure 1.2.18). Note 1 to entry: Helix angles may be classified as normal, slow and quick.Figure 1.2.18lead of helix helix angle Side Rake - The angle between a face and a plane passing through the selected point on the cutting edge and the drill axis, measured in the plane perpendicular to the radius at the selected point (Figure 1.2.19).Note 1 to entry: When the selected point is at the outer corner, this angle is equivalent to the helix angle (Figure 1.2.18).Side Clearance of The Major Cutting Edge - The angle between a flank and a plane containing the cutting edge and the assumed direction of primary motion at the selected point on the cutting edge, measured in the plane perpendicular to the radius at the selected point (Figure 1.2.19). This angle is usually specified and measured at the outer corner.Figure 1.2.19side rake side clearance of the major cutting edge