Machine tool spindles are rotating components that are used to hold and drive cutting tools or workpieces on lathes, milling machines and other machine tools. They use belt, gear, motorized, hydraulic or pneumatic drives and are available in a variety of configurations. For example, cartridge assemblies are housed in a stationary enclosure while angled spindles are configured to allow right angle or adjustable tool rotation. Some machine tool spindles are housed in a solid block or box-like housing. Others are bolted down via flanges or feet at the bottom of the housing.

Most machine tool spindles that fit the heads of cutting tools feature a Morse taper or other standardized machine tool taper. Multiple spindle heads are used to speed machining operations and in repetitive precision work such as close-tolerance center holes. A variety of bearing types are used with machine tool spindles. Examples include:

• Air bearings
• Angular contact bearings
• Ceramic hybrid bearings
• Hydrostatic bearings
• Magnetic bearings
• Roller bearings
• Tapered roller bearings

Specifications

Selecting machine tool spindles requires an analysis of performance specifications, tool mounting, and spindle features. Performance specifications include:

• Operating speed
• Spindle power
• Maximum torque
• Input voltage

Tool mounting measurements such as outer diameter (OD) and inner diameter (ID) are measured in either English units such as inches or metric units such as centimeters. Spindle interface size is the diameter of the cutting tool or the bore of the grinding wheel to which the spindle is mounted. Tool or work holder mounting style describes the spindle’s mounting interface. Examples include standard, threaded, and flanged bores; arbors and shafts; collets and wheel collets; and external and internal tapers.

In terms of features, some machine tool spindles include air purging or automatic balancing options. Others include high frequency drives that are liquid cooled for improved heat dissipation. Spindles with coolant feeds are also available. Machine tool spindles that are capable of axial, linear, or compound movements are used in some machining operations. Spindles with encoders or resolvers provide feedback about position and/or speed. 

Applications

Machine tool spindles are used in a variety of applications.

• Boring spindles are used in the machining of internal diameters.
• Drilling spindles provide good thrust capacity and radial load ratings.
• Grinding spindles are used with grinding wheels for precision, size and surface finishing.
• Wheel dressing spindles are suitable for the truing, dressing, contouring, and re-profiling of abrasive grinding wheels.
• Tapping spindles are used with taps to create internal threads.
• Tuning spindles are designed for horizontal or vertical lathes and turning centers.
• Hobbing spindles are used in the cutting of gear tooth profiles.
• Milling spindles are used with a wide variety of machining tools and operations.

Machine tools spindles that are used in test systems are suitable for activities such as dynamic balancing and the testing of computer drives and semiconductors. Other specialized machine tool spindles are used in applications such as jewelry manufacturing and optical lens processing. 

Standards

DIN 69001-13 - Machine tools; Multi-spindle heads; Assemblies, Boring spindles Types A to D

DIN 69001-33 - Machine tools; Multi-spindle heads; Boring spindles Types A and B

Image Credit:

Aerotech, Inc.