Jobber Length Drills Series

Better chip ejection in low carbon, non-ferrous materials.  They have good centering properties and requiers little pressure.  Heavy duty, d ≧ 3mm, 135° split point

#Cutting tools#-#Hole making tool#  

#Twist drill# is the most commonly used hole making tool. This kind of drill has a long linear main cutting edge. The two main cutting edges are connected by a cross edge and the chip groove is spiral shape (to facilitate chip removal).  

Part of the spiral groove constitutes the front cutter face, and the front cutter face and the top Angle determine the size of the front Angle. Therefore, the front Angle of drilling tip is not only closely related to the helix Angle, but also affected by the Angle of edge. 

The helix angle of ordinary twist drills mainly affects the size of the rake angle on the cutting edge, the strength of the blade blade and the chip removal performance, usually 25° to 32°. The spiral groove can be processed by milling, grinding, hot rolling or hot extrusion, and the front end of the drill bit is sharpened to form a cutting part. The apex angle of the cutting part of the standard ordinary twist drill is 118°, the bevel angle of the chisel edge is 40°-60°, and the relief angle is 8°-20°. Due to structural reasons, the rake angle is large at the outer edge and gradually decreases towards the middle, and the chisel edge has a negative rake angle (up to -55°), which acts as a squeeze during drilling. In order to improve the cutting performance of the twist drill, the cutting part can be ground into various shapes(such as group drills) according to the nature of the processed material. The shank of the twist drill has two types: straight shank and tapered shank. During processing, the former is clamped in the drill chuck, and the latter is inserted in the tapered hole of the machine tool spindle or tailstock. General twist drills are made of high speed steel. Twist drills with welded carbide blades or crowns are suitable for processing cast iron, hardened steel and non-metallic materials, etc. Small solid carbide twist drills are used for processing instrument parts and printed circuit boards.