Why and How to choose taper shank drill

What’s the taper shank drill?

Taper shank drill is commonly used for drilling or reaming holes in metal or other materials. Taper shank drills are characterized by a certain taper in the shank of the drill bit, usually with a Morse taper, which can be inserted into a tapered hole in the spindle or tailstock of a machine tool to improve the rigidity and concentricity of the drill bit. The diameter range of taper shank drills is generally 0.25 to 80 millimeters, and they can be classified into the following types according to different structures, applications and materials:

1. Twist drill: it has two spiral flutes, shaped like a twist. Twist drill is the most widely used taper shank drill, can be used for drilling a variety of materials and shapes of holes. The spiral angle of twist drill mainly affects the size of the Cutting edge on the front angle, edge strength and chip removal performance, usually 25 ° ~ 32 °. The point angle is 118 °, the chisel edgel angle is 40 ° ~ 60 °, and the clearance angle is 8 ° ~ 20 °. Twist drill is generally made of high-speed steel, there are also welded carbide inserts or tooth crown of the twist drill and the whole carbide twist drill.

2.Flat drill: the cutting part is spade-shaped, simple structure, low manufacturing cost, the cutting fluid is easily going into the hole, but the cutting and chip removal performance is poor. The structure of flat drill has two types: integral type and assembly type. Integral type is mainly used for drilling micro-holes with a diameter of 0.03 to 0.5 mm. The assembled flat drill has replaceable inserts and internal cooling, and is mainly used for drilling large holes with a diameter of 25 to 500 millimeters.

3.Deep Hole Drill: Deep hole drill usually refers to tools for processing holes with a ratio of hole depth to hole diameter greater than 6. Frequently used are gun drills, BTA deep hole drills, jet drills, DF deep hole drills and so on. Core drills are also commonly used for deep hole machining. Deep hole drill generally use internal cooling and external chip removal to ensure low cutting temperature, smooth chip removal and high machining accuracy.

4.Core Drills: Core drill has 3 to 4 teeth, its rigidity is better than twist drill, used to enlarge the existing hole and improve the machining accuracy and finish. Core drills can be made of different materials and structures according to the material to be processed and the accuracy.

5.Countersinks: Countersinks have a large number of teeth and are used to shape the end of the hole to the desired shape, for machining countersunk holes for various types of screws, or for flattening the outer face of the hole.

6.Center Drill: Center Drill is used for drilling the center hole of shaft workpiece, which is essentially a composite of twist drill and countersink with small helix angle, so it is also called composite center drill. Center drills are generally used to get the center point before drilling, the front taper angle has 60 °, 75 °, 90 ° and so on. The center drill is used to improve the positioning accuracy of the drill bit and prevent the drill bit from shifting, but also to provide support for the top of the lathe.

How to use the taper shank drill?

Taper shank drills have a tapered shank and can be clamped directly to the machine tool or attached with a drill sleeve (taper sleeve). The advantage of taper shank drills is that they can transmit higher torque and are suitable for drilling holes with a diameter greater than 13 mm. The structure and principle of the taper shank drill is similar to straight shank drill, in that it drills a round hole in the workpiece by rotary cutting.

The working part of the taper shank drill consists of a cutting part and a guiding part, the cutting part has two main cutting edges and a cross cutting edge, and the guiding part has two sub-cutting edges. The cutting part of the taper shank drill has five angles: the point angle, the rake angle, the clearance angle, the tool cutting edge angle and the end face inclination angle. These angles affect drilling quality, efficiency and tool life.

Installation and removal of taper shank drills should be in line with the Morse taper hole of the machine spindle, otherwise it will cause eccentricity or loosening. When installing, tap gently to make the taper surface fit closely; when disassembling, use an inclined iron to strike to dismount, not to strike the drill directly.

Taper shank drill is a kind of tool whose shank is matched with the taper hole of the machine tool spindle, and it mainly has various standards and specifications such as SK, HSK, BT, NT, JT, IT, CAT and so on. The advantage of taper shank drilling is that it can realize quick loading and unloading of tools, improve the positioning accuracy and connection rigidity of tools, and is suitable for all kinds of drilling, milling, tapping and other machining. The disadvantage of taper shank drills is that the taper hole of the spindle expands when rotating at high speed, which affects the repeatability of positioning accuracy and cutting stability, and each specification of taper shank drills can only be clamped with one diameter of tool, which is not flexible enough.

Taper shank drills are widely used in machining centers, CNC machine tools, CNC milling machines and other machining equipment, and can be used to clamp a variety of straight shank tools, such as twist drills, reaming drills, countersinking drills, center drills, milling cutters, taps and so on. According to different standards and specifications, taper shank drills can be adapted to different machining requirements and conditions, such as SK general purpose shanks for general machining, HSK vacuum shanks for high-speed machining, BT-type shanks for Japanese-standard machine tools, and CAT-type shanks for U.S.-standard machine tools.

How to choose the taper Shank drill bits?

Choosing the right taper shank drill based on following considerations:

1.The diameter and depth of the drilled hole.

Generally speaking, holes with a diameter greater than 13mm are suitable for taper shank drill, because taper shank drill can transmit greater torque, while holes with a diameter less than 13mm are suitable for straight shank drill bits ,because straight shank drilling can be clamped more easily.

2.Material and hardness of drilling.

Different materials and hardnesses require the selection of different drill materials and cutting edge angles. Generally speaking, there are two kinds of drill materials, high-speed steel and cemented carbide. High-speed steel is suitable for drilling low-hardness materials, such as iron, copper, aluminum and so on, and cemented carbide is suitable for drilling high-hardness materials, such as stainless steel, alloy steel and so on. The cutting edge angle should also be adjusted according to the nature of the material. Generally speaking, soft materials need a larger cutting edge angle, and hard materials need a smaller cutting edge angle.

3.Precision and surface quality of drilled holes.

Different accuracy and surface quality requirements require the selection of different drill types and cutting parameters. Generally twist drills are the most common one for roughing and medium machining, but with lower precision and surface quality. If high precision and high surface quality drilling is required, other types of drills such as center drills, reaming drills and reamers can be used for pre-machining or finishing. Cutting parameters mainly include cutting speed, feed and coolant, which affect the efficiency, quality and tool life of the drilled holes. Generally speaking, cutting speed should be selected according to the hardness and thermal conductivity of the material, feed should be selected according to the diameter of the drill and cutting force, and coolant should be selected according to the nature of the material and cutting temperature.