Collets

The function of the SK interface

The steep taper is the original among tool interfaces and is still frequently used today in the machine tool industry for automatic tool change. Despite the increasing spread of the HSK interface, the SK interface still represents a practical solution for standard machine tools.

With SK technology, clamping in the machine tool spindle takes place via a tightening bolt. The centering of the shank in the sleeve takes place exclusively via the taper surface. Due to this characteristic, the use of the steep taper is limited to a speed of 12,000 rpm. In general, the steep taper is a very robust form-fit connection. The most common form of steep taper is the DIN 69871 Form A with trapezoidal groove and orientation groove. The steep taper is available in 6 main sizes: SK 30, SK 35, SK 40, SK 45, SK 50, SK 60.

The disadvantage of the SK interface

Although the SK interface enables automatic tool change, it cannot take full advantage of the capabilities of modern machine tools. The reason for this is that at higher speeds, the shaft expands in the area of the spindle head under the influence of centrifugal force. At the same time, the solid tool shank does not expand significantly, resulting in radial play between the shaft and the tool. As a result, the tool is pulled further into the spindle, which is why the tool may be undetachably tight in the shaft at standstill.

The concentricity, power transmission and positional accuracy of the spindle mandrel also decrease at higher revolutions. Chatter marks on the surface of the workpiece and reduced dimensional accuracy on the component are the result.