HSK taper on CNCs – what is it ?

Written By Ashish Kumar S

November 5, 2025

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CNC: HSK holder taper – what is it, and how is it different ?

The HSK taper is relatively new compared to BT, CAT and ISO.

The taper on HSK is hollow and short, with a taper of 1/10 or 5.72 degrees (as against 7/24 or 16.26 degrees on BT, CAT and ISO – see this earlier post).

The short taper enables a faster tool change and keeps the bearing of the machine spindle compact, close to where the machining is actually being done. The taper holding area of the machine spindle expands at higher speeds due to centrifugal force, causing a ‘bell-mouth’ effect in older systems. The HSK’s hollow taper expands with the machine spindle, reducing the bell-mouth effect.

The face on the holder butts against the spindle face, ensuring that the tool holder cannot be sucked up into the spindle farther when run at high speeds. Z dimensions on the part are hence accurately controlled.

HSK holders come in several sizes, HSK32 to HSK100. The number is actually the largest dimension on the holder.

Text and pics. source: CADEM NCyclopedia multimedia CNC training software.

Author

Ashish Kumar S

cadem

Ashish brings strong techno-commercial depth across CNC productivity solutions, CAD/CAM systems, and skill development initiatives. As the face of CADEM’s CNC ecosystem, he drives solution adoption and market growth by aligning advanced manufacturing software with real-world production challenges. A passionate advocate of CNC education in India, he actively engages with customers and students to bridge the gap between industry needs and workforce readiness.

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