1:10 short hollow taper with simultaneous flange face and taper dual contact.
Centrifugal force at high RPM (15,000 to 40,000+ RPM) expands the internal gripper fingers, increasing clamping force dynamically.
Axially and radially balanced for high-speed machining (HSM).
BT40 / CAT40 (7:24 Steep Taper - ISO 7388):
Deep solid steep taper providing high bending moment resistance for heavy low-RPM roughing.
BBT (Big-Plus) variants provide dual face and taper contact, bridging the gap between BT and HSK rigidity.
Centrifugal Expansion at High RPM
On standard BT40 spindles, centrifugal expansion widens the spindle bore at 12,000+ RPM, causing solid toolholders to pull deeper into the spindle and creating Z-axis depth variance. HSK completely eliminates this effect.
Frequently Asked Questions
Why does HSK tool clamping force increase as spindle speed increases?
The internal segmented gripper fingers are driven outward by centrifugal force, pushing harder against the internal taper chamber as RPM rises.
What is the advantage of BBT (Big-Plus) over standard BT toolholders?
BBT contacts both the spindle taper and the spindle face simultaneously, increasing radial bending stiffness by over 200% compared to standard taper-only BT40.
