Twist drill, and method and device for grinding twist drills

摘要

419,698. Twist drills. WESSELMANNBOHRER CO. AKT.-GES., Gera-Zwotzen, and BECKMANN, J., 8, Zeulsdorfer Strasse, Gera- Lusan, both in Germany. Jan. 26, 1934, No. 2781. [Class 83 (iii).] The conical end faces of the lands of a twist drill are ground away on curved surfaces c to allow access of lubricant to the cutting edges b and to provide two transverse cutting edges d meeting at the centre point a. The line i at the junction of the surface c with the conical surface is a curve, convex towards the cutting edge b, and extends from the centre to the circumference of the drill, and the relief on the conical surface is less than that usually provided on twist drills.