What are the types of drill bits

- Dec 14, 2020-

What are the types of drill bits? The characteristics and uses of various types of drill bits are introduced

    twist drill

    Twist drill is the most widely used hole machining tool. Usually the diameter ranges from 0.25 to 80 mm. It is mainly composed of the working part of the drill bit and the handle. The working part has two spiral grooves, which resemble 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 shank to form an inverted cone shape. The helix angle of the twist drill mainly affects the size of the rake angle on the cutting edge, the strength of the blade and the chip removal performance, usually 25°~32°. The spiral groove can be processed by milling, grinding, hot rolling or hot extrusion. The front end of the drill bit is sharpened to form a cutting part. The apex angle of the cutting part of the standard twist drill is 118, the chisel edge bevel angle 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 toward the middle. The chisel edge has a negative rake angle (up to about -55°), which acts as a squeeze during drilling.

    In order to improve the cutting performance of twist drills, the cutting part can be ground into various shapes (such as group drills) according to the nature of the material being processed. The shank of twist drill has two types: straight shank and taper shank. The former is clamped in the drill chuck during processing, and the latter is inserted into the taper hole of the machine tool spindle or tailstock. Generally, twist drills are made of high-speed steel. Twist drills with welded hard alloy blades or crowns are suitable for processing cast iron, hardened steel and non-metallic materials, and small solid hard alloy twist drills are used for processing instrument parts and printed circuit boards.

    Flat drill

    The cutting part of the flat drill is spade-shaped, simple in structure, low in manufacturing cost, and cutting fluid is easily introduced into the hole, but the cutting and chip removal performance is poor. The structure of the flat drill has two kinds of integral type and assembly type. The integral type is mainly used for drilling micro holes with a diameter of 0.03-0.5 mm. The assembled flat drill blades are replaceable and can be internally cooled. They are mainly used for drilling large holes with a diameter of 25 to 500 mm.

    Deep hole drill

    Deep hole drilling usually refers to a tool for processing holes with a ratio of hole depth to hole diameter greater than 6. Commonly used gun drills, BTA deep hole drills, jet drills, DF deep hole drills, etc. Nesting drills are also often used for deep hole processing.


    The reamer drill has 3 to 4 teeth, and its rigidity is better than that of a twist drill. It is used to expand existing holes and improve machining accuracy and smoothness.


    The countersink drill has more teeth, and the hole end is processed into the required shape by the forming method, which is used to process the countersunk hole of various countersunk screws or flatten the outer end surface of the hole.

    Center drill

    The center drill is used for drilling the center hole of the shaft workpiece. It is essentially a composite of twist drills and countersink drills with a small helix angle, so it is also called a composite center drill