HSK vs BT, SK, CAT
In the mechanical production field the best way for connecting the tool to the machine tool is a taper: the force is transmitted along the lateral surface in a more or less rigid way. The spindle drawbar pulls the homonym stud to keep in contact the 2 surfaces of the tapers.
The force required is between 15-60 kN, depending on size and norm used.
HSK is around 40 kN for HSK-A 100, the biggest model.
The main difference between the 2 solution is the way they pull the cone: HSK from the internal side, all the others managing the pull stud in the rear part of the cone.
For testing the force, during the construction of the head or the machine in general, it’s possible to use this device: the instrument has the shape of a cone and it’s connected to a mainboard with a digital display. Opening, inserting the tool and reading the value is the simple procedure.
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There are 6 kinds of HSK:
| Type | Good for |
|---|---|
| A | Automatic tool change (ATC) – default |
| B | Automatic tool change (ATC) – big torque |
| C | Manual tool change – default |
| D | Manual tool change – big torque |
| E | Low torque, very high speed |
| F | The same as “E” type |
The movement of HSK bulb, in advance, creates a fall of the gripper petal that releases the taper. During folding, the bulb, which is united with the gripper, fixes the latter against the taper, and the whole group consequently (see the scheme below).
In yellow the moving contact zone in a HSK gripper.
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Here the main differences betweeen the HSK and the other solutions:
| Feature | HSK | Other |
|---|---|---|
| Radial stiffness | 5 | 1 |
| Torsional stiffness | 1 | 1 |
| Accuracy | 1 | 1 |
| Run-out | 1.2 | 1 |
| Transmitted torque | 9000 Nm in HSK 100 | 7500 Nm |
| Presetting | Better, no change in tool tip with wear | Worse, chenge in tool tip position after wear |
| Strain | The harder you go, the more torque you transmit | The harder you go, the less torque you transmit |
| Strain at high speed | Same tool tip (no change in axial position) | Change in tool tip position because of centrifugal forces |
| In the event of a collision | Acts like a fuse | The force is transmitted in full |
| Service cost | High. Qualified personnel is required | Low |
| Tool change speed | Fast: the cone is light | Slow: the cone is heavy |
| Wear sensitivity | High (tighter tolerances), the personnel must be trained | Low |
| Cost | High, but the increasing demand is reducing the gap | Low |
| Coolant sensitivity at ω>> | High, because of displacement | High, because of displacement |
