Big Drill bit suit

Twist drill is the most widely used tool for hole processing. Usually, the diameter ranges from 0.25 mm to 80 mm.. It mainly consists of a working part and a handle. Part of the work has two spiral grooves, which are shaped like twists, hence the name. In order to reduce the friction between the guide part and the hole wall during drilling, the twist drill gradually decreases in diameter from the drill tip to the handle, showing an inverted cone shape. The helix angle of twist drill mainly affects the rake angle of cutting edge, blade strength and chip removal performance, usually 25 ~ 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 the cutting part. The top angle of the cutting part of the standard twist drill is 118, the bevel angle of the cross blade is 40 ~ 60 and the back angle is 8 ~ 20. Due to structural reasons, the rake angle is large at the outer edge and gradually decreases towards the middle, while the cross blade is negative rake angle (up to about-55), which acts as an extrusion during drilling. In order to improve the cutting performance of twist drills, the cutting parts can be ground into various shapes (such as group drills) according to the properties of the processed materials. There are two types of handles of twist drills: straight handle and taper handle. During processing, the former is clamped in the drill chuck, while the latter is inserted into the taper hole of the spindle or tailstock of the machine tool. General twist drills are made of high-speed steel. Twist drills with cemented carbide blades or crowns are suitable for processing cast iron, hardened steel and nonmetallic materials, etc. Small twist drills with integral cemented carbide are used for processing instrument parts and printed circuit boards, etc.