Introduction to the handle
The tool holder is a tool, which is the connection between the mechanical spindle and the tool and other accessories. At present, the main standards are BT, SK, CAPTO, BBT, HSK and other spindle models.

HSK tool holder
HSK tool system is a new type of high-speed short-tapered tool shank. Its interface adopts the method of simultaneous positioning of the taper surface and the end surface. The tool shank is empty in the HSK tool shank structure diagram. Conducive to the realization of light-weight and high-speed tool change. As shown below. Due to the use of hollow cone and end face positioning, the radial deformation difference between the spindle hole and the tool holder during high-speed machining is compensated, and the axial positioning error is completely eliminated, making high-speed and high-precision machining possible. This tool holder is more and more common in high-speed machining centers.

KM handle
The structure of the shank is similar to that of the HSK shank. It also adopts a hollow short taper structure with a taper of 1/10. It also adopts the structure diagram of the tapered KM shank and the simultaneous positioning and clamping of the end face. As shown in Figure 1.3, the main difference is the clamping mechanism used. The clamping structure of KM has applied for a US patent, which uses a larger clamping force and a higher rigidity of the system. However, because there are two symmetrical arc grooves on the tapered surface of the KM tool shank (applied when clamping), it is relatively thin, some parts have poor strength, and it requires a very large clamping force to normal work. In addition, the patent protection of the KM handle structure limits the rapid promotion and application of the system.

NC5 handle
It also adopts a hollow short-cone structure with a taper of 1/10, and also adopts the simultaneous positioning and clamping method of the conical surface and the end surface. Since the torque is transmitted by the keyway on the cylinder at the front end of the NC5 shank, and there is no keyway for transmitting torque at the rear of the shank, the axial dimension is shorter than that of the HSK shank. The biggest difference between the NC5 shank and the previous two shanks is that the shank does not use a thin-walled structure, and an intermediate taper sleeve is added to the taper surface of the shank. The KM tool holder and the HSK tool holder compensate the manufacturing error of the tool holder and the spindle through the deformation of the thin wall, and ensure the reliable contact between the taper surface and the end face at the same time, while the NC5 tool holder achieves this purpose through the axial movement of the middle taper sleeve. The axial movement power of the intermediate taper sleeve comes from the disc spring on the end face of the tool shank. Due to the strong error compensation ability of the intermediate taper sleeve, the NC5 tool holder has slightly lower requirements on the manufacturing accuracy of the spindle and the tool holder itself. In addition, there is only one screw hole in the NC5 shank for installing the pull stud. The hole wall is thick and the strength is high. The pressurized clamping mechanism can be used to meet the requirements of heavy cutting. The main disadvantage of this tool holder is that a contact surface is added between the tool holder and the spindle taper hole, and the positioning accuracy and rigidity of the tool holder are reduced.

CAPTO handle
CAPTO handle. The structure of this tool handle is not conical, but a triangular cone, its edges are arc-shaped, the taper is 1/20, and the hollow short cone structure adopts the simultaneous contact and positioning of the cone surface and the end surface. The triangular cone structure can realize torque transmission without slip in both directions, no need for transmission keys, and eliminates the problem of dynamic balance caused by transmission keys and keyways. The surface of the triangular cone is large, which makes the surface pressure of the tool holder low, not easy to deform, and wears little, so the accuracy is good. However, the triangular conical hole is difficult to process, the processing cost is high, it is not compatible with the existing tool holder, and the fit will self-lock.