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What are the advantages and disadvantages of twist drill bits and flat drills?
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What are the advantages and disadvantages of twist drill bits and flat drills?

Views: 129     Author: Site Editor     Publish Time: 2022-07-21      Origin: Site

A twist drill is a tool that drills a round hole in a workpiece by rotating it relative to a fixed axis. It is named after the spiral shape of its chip groove, which resembles a twist. There are 2, 3 or more spiral grooves, but 2 grooves are the most common. The twist drill can be clamped to a manual or electric hand-held drilling tool or to a drill press, milling machine, lathe or even a machining center.


The cutting part of the flat drill is ground into a flat body, with the main cutting edge sharpened to a sharp angle and back angle and forming a cross edge; the secondary cutting edge is sharpened to a back angle and sub-deflection and to control the drilling diameter. The flat drill has a small front angle, no spiral groove, and difficult chip removal, but it is simple to manufacture and low cost, and is widely used for processing small holes with a diameter of 1mm or less. Flat drills are also used in automatic lines and CNC machines for machining holes with a diameter of 35mm or more due to the large structural improvements and the above-mentioned advantages.

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What is a twist drill? What is a conventional flat drill? How to distinguish twist drill from conventional flat drill.


Disadvantages of twist drill: (1) The difference in the value of the front angle at each point on the main cutting edge of the standard twist drillis too large, both inside and outside. The front angle of the main cutting edge at the outer edge of the drill is about +30°; while near the center of the drill, the front angle is about -30°. The front angle near the center of the drill is too small, resulting in large chip deformation and high cutting resistance; while the front angle near the outer edge is too large, and the cutting edge strength is often too low when processing hard materials.


(2) The cross-edge is too long, the front angle of the cross-edge is very negative, up to -54 ° ~ -60 °, which will produce a large axial force.


(3) Compared with other types of cutting tools, the main cutting edge of the standard twist drill is very long, which is not conducive to chip separation and chip breaking.


(4) The secondary cutting edge at the edge belt has a zero value of the secondary back angle, resulting in increased friction between the secondary back tool surface and the hole wall, increased cutting temperature, greater wear at the outer edge of the drill corner, and deterioration of the machined surface roughness.


The above defects often make the twist drill wear fast, which seriously affects the drilling efficiency and the improvement of the machined surface quality. Disadvantages of flat drill: The traditional flat drill is made of high-speed steel, and the cutting speed is low.


Due to the limitation of the integral structure, the working front angle of the flat drill is negative, and the axial force and torque are large; its guidance mainly depends on the positioning guide key (rear guide structure) on the flat drill chuck, which is unstable and easy to deviate; the cutting edge of the flat drill adopts a symmetrical structure, which cannot effectively divide the thickness of the cutting layer. When drilling solid parts, if the flat drill tip is blunt, it is possible to form extrusion on the surface of the workpiece, which will cause a sudden increase in drilling force and torque, resulting in the occurrence of chipping and the scrapping of the flat drill as a whole.