CNC machines are machine tools run by a computer instead of a hand on a crank. The term covers dozens of machines, but most of them fall into six families: turning, milling, multi-axis, spark and abrasive, large-part, and sheet and plate. This guide walks through each family: what the machines do, what parts they make, and the specs that separate one type from the next.
Machine Tool Exchange buys used CNC machines directly from the shops and plants that run them, so this guide is written from the owner's side of the machine, not a new-machine catalog.
What Is a CNC Machine?
A CNC machine is a machine tool whose movements are controlled by a computer. CNC stands for computer numerical control: the control reads a program, usually written in G-code, and drives the motors that move the tool and the workpiece. The first numerically controlled machines were built in the 1940s and 1950s from existing machine tools fitted with motors.
The program is a list of coordinates and commands. A line such as G01 tells the machine to move in a straight line at a set feed rate, G00 is a rapid move, and G02 and G03 cut arcs. Because the same program runs the same way every time, a CNC machine can repeat a part hundreds of times with the same result.
Every CNC machine shares three pieces: a control (the computer and its screen), drives and motors on each axis, and the machine tool itself. What changes from one type to the next is how the machine removes material. On a lathe the work spins; on a mill the tool spins; an EDM cuts with electrical sparks; a grinder uses an abrasive wheel. For the processes behind those machines (turning, milling, drilling, boring), see our guide to machining processes and tools.
What Are the Main Types of CNC Machines?
The main types of CNC machines are lathes and turning centers, machining centers (vertical and horizontal), 5-axis and multi-tasking machines, EDMs, grinders, large-part machines such as horizontal boring mills and vertical turret lathes, and sheet and plate machines such as lasers, plasma cutters, waterjets and press brakes.
| Family | Machine | How it removes material | Typical parts |
|---|---|---|---|
| Turning | CNC lathe, turning center, Swiss-type lathe | The workpiece spins; a non-rotating tool is fed into it | Shafts, pins, bushings, fittings, round parts |
| Milling | Vertical machining center (VMC), horizontal machining center (HMC) | A spinning tool moves across a clamped workpiece | Brackets, housings, plates, molds |
| Multi-axis | 5-axis machining center, mill-turn (multi-tasking) machine | Milling and turning with extra rotary axes | Impellers, complex aerospace and medical parts |
| Spark and abrasive | Wire EDM, sinker EDM, surface and cylindrical grinders | Electrical sparks or an abrasive wheel | Dies, punches, hardened parts, tight-tolerance finishes |
| Large-part | Horizontal boring mill, vertical turret lathe (VTL), gantry mill | Same cuts as above, on a much bigger frame | Frames, large rings, housings, castings |
| Sheet and plate | Laser, plasma, waterjet, press brake, punch press | Cutting or forming flat stock | Flat blanks, bent parts, enclosures |
Most machine shops are built around the first two families. A job shop typically runs a mix of lathes and machining centers, and adds EDM, grinding or 5-axis capacity as its work gets more demanding.
If you own one of these machines and are thinking about selling it, Machine Tool Exchange buys them directly. Tell us what you have or call 800-822-9524.
What Does a CNC Lathe or Turning Center Do?
A CNC lathe spins the workpiece and feeds a non-rotating cutting tool against it, which makes it the machine for round parts: shafts, pins, bushings, threaded fittings. A turning center is an enclosed, production CNC lathe with a tool turret; many add powered (live) tools, a C axis or a second spindle so they can drill and mill as well as turn.
Lathes are among the oldest machine tools on a shop floor. The CNC version replaced the hand wheels with servo motors on two main axes: Z, which runs along the spindle, and X, which moves the tool in and out to set the diameter. From there the family branches:
- CNC lathes (2-axis): turning, facing, boring and threading on bar stock or chucked work. See our CNC lathe category.
- Turning centers: enclosed production lathes; many add live tooling, a C axis to index the spindle, or a sub-spindle that catches the part at cutoff to finish the back side. See CNC turning centers.
- Swiss-type lathes: the bar feeds through a guide bushing that supports it right next to the tool, so long, slender parts stay accurate. The design came out of 19th-century Swiss watchmaking. See Swiss-type lathes.
- Vertical turret lathes: a lathe stood on end, covered below under large-part machines.
For a full walk-through of lathe parts, axes and types, read what a lathe is and how CNC lathes work.
What Is a CNC Machining Center?
A CNC machining center is a CNC mill with an automatic tool changer. The workpiece is clamped to a table, a spinning cutting tool removes material, and the machine swaps tools on its own between operations. The two main kinds are the vertical machining center (VMC) and the horizontal machining center (HMC).
VMC vs HMC. The difference is the direction of the spindle. On a VMC the spindle points straight down at the table, which makes setups easy to see and load, and suits plates, molds and one-off parts. On an HMC the spindle points sideways; chips fall away from the work, and most HMCs carry a pallet changer so the operator can load the next part while the machine cuts the current one. That tends to make the HMC the choice for long production runs and the VMC the more flexible, general-purpose machine.
Both are 3-axis machines at their most basic. Z always runs along the spindle: on a VMC, X is left and right, Y is front to back and Z is up and down; on an HMC, Z runs in and out along the horizontal spindle and Y is up and down. A rotary table adds a fourth axis. Our category pages cover vertical machining centers and horizontal machining centers.
What Are 5-Axis and Multi-Tasking Machines?
A 5-axis machining center adds two rotary axes to the three straight-line axes of a standard mill, so the tool can reach five sides of a part and cut compound angles in one setup. A multi-tasking (mill-turn) machine combines a turning spindle with a milling head, so one machine turns a part and mills its features without moving it to a second machine.
The two rotary axes on a 5-axis machine sit in a tilting trunnion table, in a tilting spindle head, or one in each, and are named A, B or C depending on which straight-line axis they turn around. The payoff is fewer setups: a part that would need four or five fixtures on a 3-axis VMC can often be finished in one or two. That is why 5-axis machines show up in aerospace, medical and mold work. See our 5-axis machining centers page.
Mill-turn machines come at the same problem from the lathe side. They start as a turning center and add a milling spindle with its own axes, often including a B axis that tilts the milling head. A multi-axis lathe with live tooling, a Y axis and a sub-spindle sits between a plain turning center and a full mill-turn. See multi-tasking machines.
What Do EDM and Grinding Machines Do?
EDM and grinding machines remove material without a conventional cutting edge. An EDM (electrical discharge machine) cuts with repeated electrical sparks and works on electrically conductive metals, including hardened steel. A CNC grinder removes material with a spinning abrasive wheel to reach tight tolerances and fine surface finishes.
There are two main kinds of EDM:
- Wire EDM: a thin wire, usually brass, runs through the workpiece in a tank of deionized water and cuts a profile, like a very precise band saw that never touches the part.
- Sinker EDM (ram EDM): a shaped electrode is lowered into the workpiece in a bath of dielectric oil and burns its own shape into it, which is how mold cavities and blind shapes are made.
Grinders split by the surface they finish. Surface grinders finish flat faces; cylindrical grinders finish the outside or inside diameter of round parts; tool and cutter grinders sharpen and make cutting tools. See our pages on EDM machines and CNC grinding machines.
Which CNC Machines Handle Very Large Parts?
Horizontal boring mills, vertical turret lathes and gantry mills handle parts too big or heavy for a standard lathe or machining center. They make the same cuts on a much larger frame: a boring mill bores and mills large housings, a VTL turns large rings and discs, and a gantry mill machines long, wide workpieces under a bridge.
A horizontal boring mill has a horizontal spindle that can extend out of its head (the quill or boring bar) to reach deep into a large casting. A vertical turret lathe (VTL) stands the lathe on end: the workpiece sits on a rotating table and the tools come down from above, so gravity helps seat heavy parts on the table. A gantry mill runs its spindle on a bridge that spans the table. See horizontal boring mills and vertical turret lathes.
What About Sheet and Plate Machines?
Sheet and plate machines cut or form flat stock rather than machining solid blocks. CNC laser cutters, plasma cutters and waterjets cut flat profiles; CNC press brakes bend sheet into shapes; punch presses punch holes and features. These machines anchor fabrication shops rather than machine shops.
The cutting machines differ by what they cut with: a laser uses a focused beam, a plasma cutter uses an electric arc that turns a jet of gas into superheated, electrically conductive plasma, and a waterjet uses a high-pressure stream of water, usually with an abrasive. A press brake then bends the cut blank into shape.
How Do You Tell Which Type of CNC Machine You Have?
The fastest way to identify a CNC machine is the manufacturer's nameplate, usually on the side of the machine or inside the electrical cabinet door. It lists the builder, the model and the serial number, and the model name usually tells you the type. The control screen shows the control maker and software version.
If you are writing down a machine's details, for your own records, an appraisal or a sale, these are the facts that define it:
- Builder, model and serial number from the nameplate.
- Year of manufacture, also on the nameplate or in the manual.
- Control make and model (Fanuc, Mazatrol, Okuma OSP, Haas, Siemens, Heidenhain).
- Type and axes: lathe, VMC, HMC, 5-axis, mill-turn; number of axes.
- Size: travels (X, Y, Z) for a mill; swing and distance between centers for a lathe; table size for a VTL or boring mill.
- Options: live tooling, sub-spindle, Y axis, pallet changer, through-spindle coolant, bar feeder, probing.
- Spindle hours, if the control logs them, and any service records.
With that list in hand, anyone who buys or values used machines can place your machine quickly.
Frequently Asked Questions
What are the 5 most common types of CNC machines?
Lists vary, but the five most often named are CNC lathes, CNC mills (machining centers), CNC routers, CNC laser cutters and CNC plasma cutters. In a metalworking machine shop, lathes and vertical machining centers are usually the core machines, with EDM, grinding and 5-axis added for harder work.
What is the difference between a CNC lathe and a CNC mill?
On a CNC lathe, the workpiece spins and the cutting tool does not, so it makes round parts. On a CNC mill or machining center, the tool spins and the workpiece is clamped to a table, so it makes flat faces, pockets, slots and holes. Turning centers with live tooling and mill-turn machines combine the two.
What is the difference between a VMC and an HMC?
A VMC's spindle is vertical, pointing down at the table; an HMC's spindle is horizontal. VMCs are simpler to set up and suit a wide mix of parts. HMCs clear chips better and usually have pallet changers, which suits long production runs.
What does 5-axis mean on a CNC machine?
It means the machine can move along five axes: the three straight-line axes (X, Y and Z) plus two rotary axes that tilt or turn the part or the spindle. Some machines move all five at once; others lock the rotary axes in position for each cut (3+2 machining). Either way the tool can reach five sides of a part in one setup.
Does Machine Tool Exchange buy every type of CNC machine?
Machine Tool Exchange buys used CNC machines across these families, including lathes, turning centers, machining centers, 5-axis and multi-tasking machines, EDMs, grinders, large-part machines and laser cutters. Send the nameplate details through the quote form or call 800-822-9524, and we will tell you how your machine fits.
Own one of these machines and thinking about selling it? Machine Tool Exchange buys used CNC machines directly, so you deal with the buyer, not a middleman. Get a quote for your machine or call 800-822-9524.