Introduction To The Characteristics And Applications Of Various Types Of Drill Bits

twist drill
The Fried Dough Twist drill is the most widely used tool for hole machining. Its diameter range is typically from 0.25 to 80 millimeters. It is mainly composed of the working part of the drill and the shank.
The working part has two spiral grooves, resembling Fried Dough Twists, hence the name. To reduce the friction between the guiding part and the hole wall during drilling, the diameter of the Fried Dough Twist drill gradually decreases from the drill point towards the shank, forming an inverted cone shape. The helix angle of the Fried Dough Twist drill mainly affects the size of the rake angle on the cutting edge, the strength of the edge petals, and the chip removal performance, typically ranging from 25° to 32°. The spiral grooves can be processed by milling, grinding, hot rolling, or hot extrusion. The front end of the drill is ground to form the cutting part. The standard Fried Dough Twist drill has a cutting part with a vertex angle of 118°, a cross-edge bevel angle of 40° to 60°, and a clearance angle of 8° to 20°. Due to structural reasons, the rake angle is larger at the outer edge and gradually decreases towards the center, with a negative rake angle at the cross-edge (up to about -55°), which exerts a squeezing effect during drilling.
To improve the cutting performance of Fried Dough Twists, the cutting part can be ground into various shapes (such as cluster drills) according to the properties of the material being processed. Fried Dough Twists come in two types of shank forms: straight shank and taper shank. During processing, the former is clamped in a drill chuck, while the latter is inserted into the taper hole of the machine tool spindle or tailstock. Generally, Fried Dough Twists are made of high-speed steel. Fried Dough Twists with carbide inserts or tooth crowns are suitable for machining cast iron, hardened steel, and non-metallic materials. Small solid carbide Fried Dough Twists are used for machining instrument parts and printed circuit boards.
Flat diamond
The cutting part of a flat drill is shaped like a shovel, featuring a simple structure and low manufacturing cost. Cutting fluid can be easily introduced into the hole, but its cutting and chip removal performance is poor. There are two types of flat drill structures: integral and assembled. The integral type is mainly used for drilling micro-holes with diameters ranging from 0.03 to 0.5 millimeters. The assembled flat drill insert is replaceable and can adopt internal cooling, mainly used for drilling large holes with diameters ranging from 25 to 500 millimeters.
deep hole drill
Deep hole drills typically refer to tools used for machining holes where the ratio of hole depth to hole diameter is greater than 6. Commonly used deep hole drills include gun drills, BTA deep hole drills, jet drills, and DF deep hole drills. Nest drills are also commonly used for deep hole machining.
reamer
The reamer has 3 to 4 cutting teeth, and its rigidity is better than that of a Fried Dough Twist drill. It is used to enlarge existing holes and improve machining accuracy and surface finish.
Spot drilling
The spot facer has a large number of cutting teeth, which can process the hole end into the required shape by forming method. It is used to process the countersunk head holes of various countersunk head screws, or to flatten the outer end surface of the hole.
center drill
The center drill is used for drilling the center hole of shaft-type workpieces. It is essentially a combination of a Fried Dough Twists drill with a very small helix angle and a spot drill, hence it is also known as a composite center drill.