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Countersink Drill Bit (220)

Countersink Drill Bit
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As the name suggests, a drill bit refers to a tool used for drilling or reaming. This type of drill bit is generally made of metal and is a tool used to drill through holes or blind holes in solid materials.

A drill bit, comprising a shank ⑴, the shank has a tip, and the tip has two cutting blades (5, 5') located on a principal plane (C-C), the cutting blades (5, 5') Has a short central cutting edge oriented in a common second plane (E-E). The cutting edge forms a point-shaped central cutting edge for entering the workpiece and thereby centering the drill bit. On the tool bar, two chip flutes (6, 6') are provided, and the chip flutes (6, 6') extend from the tip to the bottom. On any cross-section along the arbor, the chip flutes are located at the position diametrically opposite to each other on the tube plane, and the tube plane and the common land plane (F-F) of the two land on both sides of the tube Extending at 90°, the shank has the greatest rigidity in this plane. The orientation of the second plane (E-E) of the central cutting edge is approximately 90° with the plane of the land or the main rigid direction (F-F) of the bottom end of the shank.

What are the types of drill bits

A. Classified by structure

(1) Integral drill bit: The drill top, drill body, and drill shank are integrally manufactured from the same material.

(2) End-welded drills, the top of the drill is welded by carbides.

B. Classified by drill

(1) Straight shank drills: drills with a diameter below ψ13.0mm, all use straight shanks.

(2) Taper shank drill bit: The drill bit shank is tapered, and the taper is generally Morse taper.

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C. Classification by purpose

(1) Center drill bit: generally used for centering before drilling. The front end cone has 60°, 75°, 90°, etc., in order to support the tailstock during lathe operation, the 60° center drill should be used with the tail of the lathe. The seat top center 60° matches.

(2) Twist drill bit: It is the most widely used drill bit in industrial manufacturing. We generally use twist drill bit.

(3) Super hard drill bit: The front end of the drill body or all of it is made of super hard alloy tool material, which is used for drilling of processing materials.

(4) Oil hole drill: The drill body has two small holes, through which the cutting agent reaches the cutting edge part to take away heat and chips. Use this drill to rotate the work while the drill is stationary.

(5) Deep hole drill: It was first used for the drilling of barrels and stone-clad tubes, also known as barrel drills. The deep hole drill is a straight groove type, which cuts a quarter of the strong part in a round tube to produce cutting edge chip removal.

(6) Drill bit reamer: For the needs of mass production, the front end is a drill bit and the back end is a reamer. The diameter of the drill bit and the diameter of the reamer are only the margin of the reaming hole. There are also drill bits that are used in combination with screw tapping. It is called a hybrid drill.

(7) Taper drill bit: When processing the mold feed opening, taper drill bit can be used.

(8) Cylindrical hole drill: We call it a countersunk milling cutter. The front end of this drill has a smaller diameter part called a ball.

(9) Tapered hole drill: It is used for drilling tapered holes. The front end angles are 90°, 60°, etc. The chamfering tool we use is a kind of tapered hole drill.

(10) Triangular drill: a drill used in electric drills, the drill shank is made into a triangular face, so that the chuck can secure the drill.

Introduction to the characteristics and uses of various types of drills

twist drill

Twist drill is the most widely used hole machining tool. Usually the diameter ranges from 0.25 to 80 mm. It is mainly composed of the working part of the drill bit and the shank. The working part has two spiral grooves, which resemble twists, hence the name. In order to reduce the friction between the guide part and the hole wall during drilling, the twist drill gradually decreases in diameter from the drill tip to the shank to form 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°~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 part. The top angle of the cutting part of the standard twist drill is 118, the chisel edge bevel angle is 40°-60°, and the relief angle is 8°-20°. Due to structural reasons, the rake angle is large at the outer edge and gradually decreases toward the middle. The chisel edge has a negative rake angle (up to about -55°), which acts as a squeeze during drilling.

In order to improve the cutting performance of twist drills, the cutting part can be ground into various shapes (such as group drills) according to the nature of the material being processed. The shank of the twist drill has two types: straight shank and tapered shank. The former is clamped in the drill chuck during processing, and the latter is inserted in the taper hole of the spindle or tailstock of the machine tool. Generally, twist drills are made of high-speed steel. Twist drills with welded carbide blades or tooth crowns are suitable for processing cast iron, hardened steel and non-metallic materials, and solid carbide twist drills are used for processing instrument parts and printed circuit boards.

Flat drill

The cutting part of the flat drill is spade-shaped, simple in structure, low in manufacturing cost, and cutting fluid is easily introduced 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 micro-holes with a diameter of 0.03-0.5 mm. The assembled flat drill blades are replaceable and can be internally cooled. They are mainly used for drilling large holes with a diameter of 25 to 500 mm.

Deep hole drill

Deep hole drilling usually refers to a tool for processing holes with a ratio of hole depth to hole diameter greater than 6. Commonly used gun drills, BTA deep hole drills, jet drills, DF deep hole drills, etc. Nested drills are also often used for deep hole processing.


The reamer drill has 3 to 4 teeth, and its rigidity is better than that of a twist drill. It is used to expand the existing hole and improve the processing accuracy and smoothness.


The countersink drill has more teeth, and the hole end is processed into the required shape by the forming method, which is used to process the countersunk hole of various countersunk screws or flatten the outer end surface of the hole.

Center drill

The center drill is used to drill the center hole of the shaft workpiece. It is essentially a composite of twist drills and counter drills with a small helix angle, so it is also called a composite center drill.

How to use the drill

The drill bit is a tool used to drill through holes or blind holes in solid materials and ream existing holes. Commonly used drills mainly include twist drills, flat drills, center drills, deep hole drills and nest drills. Different drill bits have different functions, how should the drill bits be used? What problems should be paid attention to in the use of the drill?


The use of drill bits:

1. The drill bit should be packed in a special packaging box to avoid vibration and collision.

2. When in use, take out the drill bit from the packing box and install it into the spring chuck of the spindle or the tool magazine for automatic drill bit replacement. Put it back in the box immediately after use.

3. To measure the diameter of the drill bit, use a non-contact measuring instrument such as a tool microscope to prevent the cutting edge from contacting with the mechanical measuring instrument and being bumped.

4. Some CNC drilling machines use positioning rings. Some CNC drilling machines do not use positioning rings. If positioning rings are used, the depth positioning during installation must be accurate. If positioning rings are not used, the elongation of the drill bit on the spindle must be adjusted. Consistent, multi-spindle drilling machine should pay more attention to this point, so that the drilling depth of each spindle should be the same. If it is inconsistent, it may cause the drill bit to drill to the table or fail to drill through the circuit board, resulting in scrap.

5. At ordinary times, a 40x stereo microscope can be used to check the wear of the cutting edge of the drill.

6. Frequently check the concentricity of the spindle and the collet chuck and the clamping force of the collet. Poor concentricity will cause small diameter drills to break and large apertures. If the clamping force is not good, it will cause the actual speed to be different from the actual speed. The set speed does not match, slipping between the chuck and the drill.

7. The clamping length of the fixed shank drill bit on the spring chuck is 4 to 5 times the diameter of the drill shank to be clamped firmly.

8. Always check the spindle presser foot. The contact surface of the presser foot should be horizontal and vertical to the spindle without shaking to prevent broken drills and offset holes in the drilling.

9. The dust suction effect of the drill press is better. The dust suction air can reduce the temperature of the drill bit. The colleagues take away the dust to reduce the high temperature caused by friction.

10. The substrate stack, including the upper and lower pads, should be firmly positioned and laid flat in a hole-to-slot positioning system on the workbench of the drilling machine. The use of adhesive tape should prevent the drill bit from drilling on the tape to make the drill bit adhere to the chips, causing difficulty in chip removal and broken drills.

11. When ordering the manufacturer’s drill bit, 4% of the drill bit shall be sampled to check whether it meets the requirements when entering the factory for inspection. And 100% of the nicks, scratches and cracks are inspected with a microscope of 10 to 15 times.

12. Re-grinding the drill in time can increase the use and regrind times of the drill, extend the life of the drill, and reduce the production cost and expense. Usually measured with a tool microscope, the wear depth should be less than 0.2mm within the full length of the two main cutting edges. When regrinding, 0.25mm should be removed. Ordinary fixed shank drills can be reground 3 times, and undercut drills can be reground 2 times. Too much grind will reduce the quality and accuracy of the drilling, which will cause the finished circuit board to be scrapped. Excessive grinding effect is counterproductive.

13. When due to wear and its wear diameter is reduced by 2% compared with the original, the drill bit is scrapped.

14. Drill bit parameter setting. Under normal circumstances, the manufacturer provides a parameter table of the drilling speed and lower speed of the drill bit produced by the factory. This parameter is only for reference. In the actual situation, the speed and down speed parameters of the drill bit are usually different from the reference parameters, but the difference is not too much.Countersink Drill Bit

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