How should a bit be selected?

Drill bits are widely used hardware in our construction machinery. They are used to drill through holes or blind holes on solid materials and to drill holes for existing holes. However, we choose different types of drill bits in different working environments. The main drill bits are twist drill, flat drill, center drill, deep hole drill and casing drill. Reaming drill and counter drill can not drill holes in solid materials, but they are traditionally classified as drill bits. Next, let’s look at the different uses of different types of drill bits together with Xiaobian.

The twist drill is the most widely used hole cutting tool. Usually the diameter ranges from 0.25 to 80 millimeters. It is mainly composed of the working part and the handle. The working part has two spiral grooves, shaped like a twist, hence its name. In order to reduce the friction between the guide part and the hole wall, the twist drill decreases gradually from the drill tip to the handle part and the diameter is inverted cone. The twist angle of twist drill mainly affects the size of the front corner, the strength of the blade edge and the chip removal performance, usually from 25 degrees to 32 degrees. Spiral grooves can be machined by milling, grinding, hot rolling or hot extrusion. The cutting edge is formed by grinding the front end of the drill bit. The cutting part of the standard twist drill is 118, the angle of the transverse blade is 40 to 60 degrees, and the rear angle is 8 ~ 20 degrees. Because of the structural reasons, the front angle is larger in the outer edge, and gradually decreases to the middle, and the transverse edge is at the negative front angle (up to about 55 degrees), and it is squeezed during drilling. In order to improve the cutting performance of twist drill, the cutting part can be grinded into various shapes (such as group drills) according to the nature of the material being processed. The handle of the twist drill has two types: the straight handle and the taper shank. The former is clamped in the drill chuck and the latter is inserted in the taper hole of the machine tool spindle or tail seat. The general twist drill is made of high speed steel. The twist drill with welded cemented carbide inserts or crowns is suitable for processing cast iron, hardened steel and non-metallic materials. The whole hard alloy twist drill is used to process instrument parts and printed circuit boards.
The cutting part of the flat drill is shovel shaped, simple in structure and low in manufacturing cost, and the cutting fluid is easily imported 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 holes with diameters of 0.03 to 0.5 millimeters. The assembled flat drill blade can be replaced, and can be internally cooled. It is mainly used for drilling large holes with a diameter of 25~500 millimeters.


Deep hole drilling usually refers to cutting the hole with a hole ratio greater than 6 to Kong Shen. Commonly used are gun drill, BTA deep hole drill, jet drill, DF deep hole drill and so on. The drill is also used in deep hole processing.


The reaming drill has 3~4 cutter teeth, which is better than the twist drill. It is used for enlarging the existing hole and improving the machining accuracy and smoothness.


The countersink drill has more cutter teeth, and the hole ends are machined into the desired shape by the forming method, which is used to process the countersunk holes of various countersunk screws or to cut the outer ends of holes.


The center drill is used for drilling the center hole of shaft parts. It is essentially made up of a twist drill with small helix angles and a counter drill, so it is also called a compound center drill.


Hollow drill pipe is hollow drill bit, which is mainly used for core drilling