Milling Machines

The milling machine – or simply mill – is a machine tool used for the machining of metal, wood, or plastic through chip and layer removal. According to DIN 8589, milling, drilling, and turning form a sub-group of machining that uses geometrically defined cuts, alongside other established production processes.

Design of a Milling Machine

1. Milling machines, milling tools, and the milling process
2. How does a milling machine work?
3. One machine, many variants
4. Second-hand milling machines: as good as new

The milling machine removes material from workpieces by rotating its cutting tool at high speed around its own axis, while either the tool moves along the desired contour or the workpiece moves accordingly. In milling, the feed movement runs perpendicularly or at an angle to the tool's rotational axis – in contrast to drilling, where the feed moves along the rotational axis, or lathe turning, where the workpiece itself rotates while the tool traces the intended contour.

The primary application for milling machines is metalworking. Because at least three feed paths can be used simultaneously, the range of complex shapes achievable is far greater than with most other machining methods. Typical applications include cutting notches and chamfers, planing surfaces and profiles, and producing complex components such as spindles, worm gears, and gear wheels – right through to heavy-duty milling of solid parts. Specialist variants are also widely used in wood and plastics processing.

• Milling machines shape metal and other materials by progressively removing outer layers, delivering high dimensional accuracy.
• The feed movement runs perpendicularly or at an angle to the tool's rotational axis, enabling a wide variety of cutting operations.
• The process is well suited to complex geometries, including spindles, gear wheels, worm gears, and profiled surfaces.

From a historical perspective, milling is a relatively recent form of metal processing. The first milling machine for metalworking was built in 1818, quickly replacing the slow and uneconomical processes of planing and filing by hand. The fundamental machine types familiar today emerged in the early 20th century – among them the tool milling machine by Deckel (1918), the gear hobbing machine by Pfauter (1912), and the groove milling machine by Hurth (1954).

Every milling machine is built around a machine body that carries all other components. Heavy-duty models are anchored to the ground via a foundation, while small- and mid-sized mills typically combine the frame and stand into a single unit – known as a mono-block design – which delivers a high level of dynamic rigidity.

Large-scale milling machines are generally built on a modular principle. Regardless of size, the milling head is the central component, capable of machining a workpiece on three sides simultaneously. Conventional machines mount a vertical or horizontal main spindle alongside a retractable tailstock, while universal milling machines allow both the slides and head to be adjusted vertically and horizontally, enabling machining at virtually any angle.

Horizontal and vertical milling spindles are well suited to light- and mid-weight workpieces, which are secured on a horizontal clamping table. Adding a cross table introduces a third axis. One common challenge with machine tables is that consoles can become unstable at end positions, which is why heavier or more complex parts are typically clamped onto beds that span the full working surface.

A CNC milling machine incorporates an automated tool-changer and a digital tailstock stroke display as standard. Modern 3- and 5-axis machining centres can produce large volumes of close-tolerance parts in minimal time. That said, conventional mills remain valuable for one-off components, small-batch production, and vocational training.

Milling machines come in a wide variety of configurations, and some overlap in function can make categorisation tricky. The following criteria provide a useful framework for distinguishing the main types:

• Spindle position (horizontal or vertical)
• Control type (conventional or CNC)
• Machine body (console, bed, or gantry design)
• Application (e.g. high-speed milling)
• Material (metal, wood, or plastic)

The following is a representative – though not exhaustive – overview of the most common milling machine types.

Knee-Type Milling Machines

A versatile standard design featuring a fixed-position spindle (horizontal or vertical), a movable worktable, and an adjustable console that allows vertical travel along the column.

Universal Milling Machines

Similar in layout to the knee-type, universal milling machines are equipped with two spindles and offer adjustable longitudinal and transverse slides, making them well-suited to a broad range of machining tasks.

CNC Machining Centres

Designed for fully automated, high-precision processing, CNC machining centres are the standard choice for serial production. Both vertical and horizontal configurations are available, with further distinctions based on machine body design.

Bed-Type Milling Machines

The rigidly fixed machine bed eliminates tipping risk, making this design well suited to heavy or bulky workpieces. Available in both conventional and CNC variants.

Gantry Milling Machines

The milling unit travels along a transverse beam supported by two uprights, providing an extended working range and excellent structural rigidity. Available in conventional and CNC versions.

Copying Milling Machines

These machines scan a physical model or template and transfer the contour directly to the milling unit, reproducing complex shapes without the need for numerical controls.

High-Speed Milling Centres (HSC)

Operating at extremely high spindle speeds and feed rates, HSC machines produce significantly thinner chips than conventional milling methods, resulting in superior surface finishes and reduced thermal stress on the workpiece.

Hobbing Machines

Hobbing is a specialised gear-cutting process also used for splines, sprockets, and offset profiles at any required angle.

Other Metalworking Variants

The metalworking category also includes long milling machines, slot and thread milling machines, engraving mills, rotary table mills, shift drum milling machines, and more.

Woodworking Milling Machines

Common woodworking variants include underfloor mills, routers, groove milling machines, table milling machines, and chain mortisers.

Second-hand milling machines offer a smart, cost-effective alternative to buying new – provided each machine undergoes a thorough inspection before purchase. Wood and metal milling machines used in industrial and craft operations typically remain in service for 20 to 30 years, and with regular maintenance and timely repairs, many older models continue to perform as reliably as they did on day one.

When evaluating a used milling machine, pay close attention to the motors, attachments, slides, and thread drives. In CNC milling machines especially, any excessive play in these components can lead to rippling and inaccuracies during climb milling. For older CNC models, software compatibility is equally important – verify that the control software works with modern computers and confirm that any licences are formally transferred to the new owner.

Used milling machines offer an excellent combination of performance and value, making them a popular choice for workshops and production facilities alike. The market covers everything from compact conventional mills to large-scale CNC machining centres, with options suited to woodworking, metalworking, and specialist serial production. Machines sourced directly from production environments require no running-in period and are typically ready for immediate use.

The most reputable milling machine manufacturers are well represented in the used equipment market, across a wide variety of models and configurations. Leading brands include:

• MAHO
• DECKEL
• HERMLE
• SORALUCE
• MIKRON
• WMW
• HAAS
• TOS
• KLOPP
• HURON
• DROOP & REIN
• KNUTH
• EMCO
• HELLER
• HURTH
• PFAUTER

When sourcing a used milling machine, it is worth considering the machine's age, spindle hours, control system compatibility, and the availability of spare parts for that manufacturer. CNC milling machines in particular benefit from a thorough review of the installed controller and any existing service documentation before purchase.