page_title: Machine taper
section_title: HSK taper
hierarchical_section_title: Machine taper / Types / HSK taper
caption_attribution_description: Hohlschaftkegel Typ A nach DIN 69893 - HSK - A63
context_page_description: A machine taper is a system for securing cutting tools or toolholders in the spindle of a machine tool or power tool. A male member of conical form fits into the female socket, which has a matching taper of equal angle.
  Almost all machine tool spindles, and many power tool spindles, have a taper as their primary method of attachment for tools. Even on many drill presses, handheld drills, and lathes, which have chucks, the chuck is attached by a taper. On drills, drill presses, and milling machines, the male member is the tool shank or toolholder shank, and the female socket is integral with the spindle. On lathes, the male may belong to the tool or to the spindle; spindle noses may have male tapers, female tapers, or both.
context_section_description: HSK toolholders were developed in the early 1990s. HSK stands for Hohlschaftkegel; German for "hollow shank tapers".
  Steep tapers tend to loosen at high speed, as their solid shanks are stiffer than the spindles they fit into, so under high centrifugal force, the spindle expands more than the toolholder which changes the overall length: That is, as the spindle 'expands' the toolholder tends to move deeper into the spindle in the z-axis which can cause the production of parts that are out-of-tolerance.  HSK's hollow shank is deliberately thin and flexible, so it expands more than the spindle and tightens when rotating at high speed. Furthermore, the HSK holder is dual contact: It engages with the spindle on both the taper and the top of the flange which prevents axial movement when thermal growth and/or centrifugal force of the spindle occurs.
  The flexibility is also used to provide accurate axial location.  An HSK toolholder has both a tapered shank, and a flange with a mating surface.  The shank is short (about half as long as other machine tapers), with a shallow taper (a ratio of 1:10), and slightly too large to allow the flange to seat fully in the socket.  The thin walls, short shank and shallow taper provide a large opening in the back of the tool.  An expanding collet fits in there, and mates with 30° chamfer inside the shank.  As the drawbar retracts, it expands the collet and pulls the shank back into the socket, compressing the shank until the flange seats against the front of the spindle.  This provides a stiff, repeatable connection because it utilizes the centrifugal force inside the spindle. As centrifugal forces increase the expanding collet within the HSK forces the walls of the toolholder shank to stay in contact with the spindle wall.
  The HSK design was developed as a nonproprietary standard. The working group that produced the HSK standard consisted of representatives from academia, the Association of German Tool Manufacturing and a group of international companies and end users. The results were the German DIN standards 69063 for the spindle and 69893 for the shank.
  The HSK working group did not adopt a specific product design, but rather a set of standards that defined HSK toolholders for different applications. The group defined a total of six HSK shank forms, in 9 sizes.
  Sizes are identified by the diameter of the shank’s flange in millimeters. These diameters are taken from the R10′ series of preferred numbers, from 25 to 160 mm.
  Today, the shank forms are designated by the letters A through F and T. The main differences between the forms are the positions of the drive slots, gripper-locating slots, coolant holes and the area of the flange.
  A is the basic form.  The B-form shank is a variant for high-torque applications, and has a flange one size larger relative to its shaft diameter.  (Thus, an A-40 shank will fit into a B-50 socket.)
  Forms C and D are simplified variants of A and B for manual use, eliminating features to accommodate automatic tool changers like a V-groove and associated orientation slots, and a recess for an RFID chip.
  Forms E and F flanges and tapers are similar to forms A and B, but designed for very high speed machining (20,000 rpm and up) of light materials by eliminating all asymmetric features to minimize imbalance and vibration.
  ASME B5.62 "Hollow Taper Tooling With Flange-Face Contact" and ISO 12164-3:2014 "Dimensions of shanks for stationary tools" include an additional form T, which is bidirectionally compatible with form A, but has a much tighter tolerance on the widths of the keys and keyways used for angular alignment.  This permits non-rotating lathe tooling to be held accurately.
  An HSK connection depends on a combination of axial clamping forces and taper-shank interference. All these forces are generated and controlled by the mating components’ design parameters. The shank and spindle both must have precisely mating tapers and faces that are square to the taper’s axis. There are several HSK clamping methods. All use some mechanism to amplify the clamping action 
caption: HSK A63 shank
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