Page 10 - Parlec Catalog

Concentricity, Rotational Speed, & Balance

8 Selection Guide

ROTATIONAL SPEED AND BALANCE

A toolholder is the interface between a precision machine spindle and a

precision cutting tool. The toolholder has three base elements; the taper

connection, the retaining device and the cutting tool connection.

TAPER DESIGN PRINCIPLES

Common toolholders for machine tool spindles today are typically one of two classes of taper; steep taper
(Cat, BT, DIN) and hollow taper (HSK).

Steep Taper
Steep Taper is the most commonly used taper principal. It is offered in different configurations, CAT, DIN, BT
or others such as SK, NMTB, etc. The steep taper is held into the spindle through the use of a retention knob
or pull stud that is affixed to the nose of the taper or by a draw bar internal to the machine spindle.

The steep taper designs are available with taper only contact or SimulFit , simultaneous taper and face
®
contact. SimulFit is available in two standard forms and can be retrofitted to any spindle even if the face is
®
not qualified.

The steep taper is also available with through the spindle coolant, or flange entry coolant. Flange entry
coolant also known as Form B or convertible Form AD/B (BC), is offered standard on many tools and available
through modification on most tools.

Steep Taper provides very good durability and excellent dampening characteristics for speeds ranging from
very low to moderately high. The typical maximum is 30,000 rpm for 30 taper, 20,000 rpm for 40 taper and
15,000 rpm for 50 taper. At higher speeds the spindle may expand due to centrifugal forces allowing the taper
to draw into the spindle. This restricts the practical speeds that steep taper can be used. The length of the
steep taper allows for a straight line bending mode based on applied side forces.

Hollow Taper

HSK tools have a much shallower taper and an internal drawbar. HSK is translated from the German name
Kegel-Holhschafte or hohl shaft kegel. HSK tools are available in many sizes and forms. Due to the face
contact (no movement allowed) and the hollow thin wall (expands to fill the spindle) of the HSK design, the
spindle speed is not restricted by draw-in of the holder due to centrifugal forces. HSK spindles can exceed
speeds of 40,000 rpm. HSK Form E and F spindles do not utilize drive keys and therefore are not practical at
lower speed, higher force applications. The short thin wall taper and face contact provide a stiffer bending
mode at lower forces and very rapid bending at higher forces. This results in a less dynamic stiffness mode.

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