How to choose a drill bit for different purposes

The Drill Bit is a widely used hardware in our engineering machinery. It is used to drill through holes or blind holes in solid materials and to ream the existing holes. However, the types of drills we choose are different in different working environments. The commonly used drills mainly include twist drills, flat drills, center drills, deep hole drills and nest drills. Although reamer and boring drills cannot drill holes in solid materials, they are customarily classified as Drill Bits. Let's take a look at the different uses of different types of drills with Xiaobian.

Twist drills are the most widely used hole machining tools. Usually the diameter ranges from 0.25 to 80 mm. It consists mainly of the working part and the handle. The working part has two spiral grooves, which are shaped like twists, hence the name. In order to reduce the friction between the guiding portion and the wall of the hole during drilling, the Twist Drill is gradually reduced in diameter toward the shank and has 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° 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 portion. The standard twist drill has a cutting edge angle of 118, a transverse blade angle of 40° to 60°, and a relief angle of 8° to 20°. For structural reasons, the rake angle is large at the outer edge and gradually decreases toward the middle, and the rake angle is a negative rake angle (up to -55°), which is squeezed during drilling. In order to improve the cutting performance of the twist drill, the cutting portion can be ground into various shapes (such as a group drill) according to the nature of the material to be processed. The handle of the twist drill has two types: a straight shank and a taper shank. The former is clamped in the drill chuck while the latter is inserted into the taper hole of the machine spindle or the tailstock. Generally twist drills are made of high speed steel. Twist drills with carbide inserts or crowns are suitable for machining cast iron, hardened steel and non-metallic materials. Solid carbide small twist drills are used to process instrument parts and printed circuit boards.

The cutting part of the flat drill has a spade shape, a simple structure, a low manufacturing cost, and the cutting fluid is easily introduced into the hole, but the cutting and chip discharging performance is poor. The structure of the flat drill is both integral and assembled. The monolith is mainly used for drilling micropores with a diameter of 0.03 to 0.5 mm. The assembled flat drill blade is replaceable and can be internally cooled. It is mainly used for drilling large holes with a diameter of 25 to 500 mm.
Deep hole drills generally refer to tools that machine holes with a hole depth to hole ratio greater than 6. Commonly used are gun drills, BTA deep hole drills, jet drills, DF deep hole drills, etc. Nesting drills are also commonly used for deep hole machining.

Reaming drills have 3 to 4 teeth and are more rigid than twist drills to expand existing holes and improve machining accuracy and finish.
The boring drill has a large number of teeth, and the hole end is processed into a desired shape by a forming method for processing the countersunk holes of various countersunk screws or flattening the outer end faces of the holes.
The center drill is used for drilling the center hole of the shaft type workpiece. It is essentially a composite of twist drill and boring drill with a small helix angle, so it is also called a composite center drill.
In the middle of the hollow drill pipe is a hollow drill bit, which is mainly used for core drilling.