Correct and skillful operation of the twist drill can not only improve work efficiency, but also ensure the safety of the operator and reduce accidents. The drill should be accurately centered in the tailstock, and should not be drilled at one time when drilling large diameter holes. When drilling deep holes, you must often exit the drill, clean up chips, drilling steel, there must be sufficient cutting fluid, will be drilled through the hole, you should slow down the feed handle to reduce the amount of feed. Master the "three must lift", that is, the lower drill encountered obstruction light turn ineffective, core clogging, drilling speed suddenly drop must lift the drill. When "slipping" is found in drilling, it is not allowed to blindly pressurize and force drilling or deal with it by dry drilling for a short period of time, and the drill should be lifted immediately. In the decompression drilling, the wire rope should be used to straighten the drill pipe and then reverse it. Before lowering the drill, the remaining feet on the machine should be matched, and it is not allowed to lift the drilling tools away from the bottom of the hole to add drilling rods in the process of return drilling. In complex rock formations, the speed of lifting the drilling tool should not be too fast, and always fill the hole with flushing liquid to prevent the hole from collapsing due to "drawing".
Twist drill is a tool for drilling round holes in workpieces by rotating and cutting relative to a fixed axis. It is named because its chip-holding groove is spiral in shape and resembles a twist. Spiral grooves have 2, 3 or more grooves, but 2 grooves are the most common. Twist drill can be clamped in manual, electric handheld drilling tools or drilling machine, milling machine, lathe and even machining centers. It belongs to the category of high-speed tool steel; its steel number is W18Cr4v; its Brinell hardness (HBS) is 207~255, and its hardened hardness is (HBC) ≥62°Forward Angle, the angle between the front face and the base face in an orthogonal plane. The relationship between the anterior angle of any selected point on the main cutting edge and the helix angle, the main deflection angle, and the edge inclination angle at that point is tan=tan/sin+tancos Eq. (2-3) As the helix angle decreases gradually from the outer radial drilling center, the edge inclination angle also decreases gradually (the negative value increases), and the anterior angle becomes smaller when the main deflection angle is certain, about from +30° to -30°, and the cutting conditions near the center of the drill bit are poor.
Back angle, the back angle of any point on the cutting edge, is the angle between the cutting plane and the back face of the point. The back angle of the drill is not measured in the main profile, but in the assumed working plane (feed profile). It is this back angle that actually plays a role in the drilling process and is easy to measure. The back angle of the drill is obtained by sharpening, and when sharpening, care should be taken to make it smaller at the outer edge (about 8°~10°) and larger near the center of the drill (about 20°~30°). The reason for such sharpening is that the back angle can be adapted to the change of the front angle of the main cutting edge, so that the wedge angle at each point is roughly equal, so as to achieve a relative balance between its sharpness, strength and durability, and to make up for the impact of the reduction of the actual back angle of the blade at each point due to the axial feed movement of the drill, and to improve the working conditions of the transverse edge.
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