Drills-carbide drilling, twist drill,milling

Drills-carbide drilling, twist drill,milling

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Twist drill

It is mainly composed of the work part and the handle part. The work part has two spiral grooves, similar to the “twist”, hence its name. In order to reduce the drilling hole wall part and the guide friction between the drill shank twist drill to self-direction decreases inverted cone diameter. The spiral angle of the twist drill mainly affects the rake angle, the blade edge strength, and the chip removal performance of the cutting edge, usually 25 to 32 degrees. The spiral groove can be processed by milling, grinding, hot rolling or hot extrusion, and the cutting edge of the drill head is formed by grinding the front end of the drill bit. The cutting edge of a standard twist drill is 118, the cross edge angle is 40 degrees to 60 degrees, and the back angle is 8 degrees to 20 degrees. As a result of structural reasons, the front angle is large at the outer edge and gradually decreases to the middle. The horizontal blade is a negative front angle (up to about 55 degrees) and plays a role of extrusion when drilling. In order to improve the cutting performance of the twist drill, the cutting parts can be cut into various shapes according to the nature of the material to be processed, such as group drills. Handle form twist drills with parallel shanks and taper shank two, when processing the former clamp the drill chuck, which is inserted in the machine tool spindle or the tail stock taper hole. Made of high-speed steel for general twist drills. Inlaid with hard alloy blade or crown drill for machining cast iron, hardened steel and non-metallic materials, solid carbide twist drill used for machining small instrument parts and printed circuit board etc..

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