Milling Machine Basics: Types, Classifications, & Cutting Tools

Calendar Icon

August 29, 2022

Author Icon

by Kennametal Metal Cutting Pros

It was cotton gin inventor Eli Whitney who’s most often attributed as the first to develop a working, dependable milling machine. The year was 1818, and Whitney, tired of the inefficient hand-filing methods of the day, needed a way to make the mass production of gun parts easier. And while his invention didn’t mark the start of the First Industrial Revolution, it certainly kicked it into high gear.

Basic Milling Functions

But what exactly does a milling machine do, and how is it different than its well-known counterpart, the lathe? Where a lathe uses a chuck to rotate a hunk of metal—usually round—against a fixed cutting tool, a milling machine is just the opposite, rotating a cutter such as a drill or end mill against a fixed workpiece.

If you operated a drill press in high school shop class or at least saw one during a trip to the local home improvement store, you already have a general idea. What’s different about milling machines is the movable table beneath—or in some cases opposite—the spindle and its attached cutting tool. This allows the machine operator to rotate a set of geared handles (or electric servo motors, in the case of a CNC machining center), thus moving the table and its attached workpiece into and around the cutter, removing material as it passes.

Milling Machine with HARVI™ I TE Ball Nose solid carbide end mill

Milling Machine Classification

In general terms, milling machines can be classified by the orientation of their spindle (or spindles, in the case of multi-spindle machining centers). In most cases, this is either horizontal or vertical, although the line has grown increasingly blurry with the development of 5-axis machining centers, so-called “nodding head” horizontal machining centers, and universal machining centers, which have both horizontal and vertically-oriented spindles. And let’s not forget that many CNC lathes today—called multitasking machines and mill-turn centers—have milling spindles or attachments, blurring the line between mill and lathe.

In the modern manufacturing world, the term “machining center” is most often used to denote CNC milling machines. Manual mills are simply called knee mills or just “milling machines.” Some die-hards refer to them as a Bridgeport, an iconic brand that has been successfully copied many times over. For the purposes of this article, we will focus on all the different types of CNC machining centers, the workhorses of modern industry.

Watch as the Mill 4-15™ indexable shoulder mill demonstrates its helical interpolation & linear ramping capabilities – achieving excellent surface quality and high metal removal rates

Types of Milling Machines

Walk into most machine shops today and you will likely see a line of 3-axis vertical machining centers. These often have three axes of motion—a spindle that moves up and down (the Z-axis), together with a table underneath that runs side to side (the X-axis) and in and out (the Y-axis).

Add a rotary table to this configuration and you now have four axes of motion (although they are rarely referred to as “4-axis machining centers”). Mount the rotary table to a swiveling trunnion arrangement (known as a tilt-rotary) and you’ve arrived at the 5-axis machining center mentioned above, able to mill parts in five axes simultaneously.

Horizontal machining centers are the darling of production shops everywhere. They’re favored due to an integrated pallet system that eliminates having to stop the machine to change workpieces. Horizontal machining centers are also very easy to automate for lights-out manufacturing, or be made part of a computer-controlled flexible manufacturing system (FMS).

Gantry mills and traveling column mills are designed for shops that need to machine very large parts, say the size of cars and tractors. Here, a vertical spindle is mounted to a horizontal rail (the Y-axis) that’s bolted to a pair of vertical pillars, forming an inverted U. If this U-shaped assembly moves on a set of rails lengthwise over a fixed table, it’s called a traveling column vertical machining center; if the table moves and the U remains stationary, it’s called a gantry type machining center. In addition, many of these machine tools come equipped with an indexable milling head, providing what’s known as five-sided machining.

Lastly, we’ll go back to horizontal machining centers for a moment. Some of these are equipped with a movable “quill” that can extend the cutting tool deep into a workpiece. These are known as boring mills, due to their ability to mill and bore very accurate holes and features in large workpieces. Again, depending on the size of the workpiece and the machine builder, these might be configured with a fixed (traveling column design) or movable table (gantry type).

Learn more about the HARVI™ I TE high-performance solid carbide end mill

Best Cutting Tools for Milling

So what types of cutting tools should be used on a milling machine? That depends on the type of machining being performed—for example, it goes without saying that a drill is needed for holemaking operations, and some type of copy mill or ball-nosed end mill is needed to machine a curved, three-dimensional surface. Beyond that, cutting tool selection is largely dependent on the amount of material being removed, its hardness, the part features, production quantity, and a host of other variables that require a good working knowledge of machining principles.

For example, anyone who wants to maximize the investment in their CNC machine tools should use solid carbide or indexable end mills, drills, and other milling cutters that are both predictable and cost-effective. In high-volume situations or in very tough materials like superalloys and hardened steels, so-called material-specific cutting tools should be selected. For lower quantities or in shops that machine a wide array of materials, more general-purpose cutting tools can be used. Whatever the machining scenario, however, the best cutting tools are those made by an experienced manufacturer using high-quality carbide, proven processes, and the support people to back these tools up.

Application specific solid carbide end mills – including KenFeed™ & GOmill™

Related Articles

You are about to add to your My Solutions page. Do you want to proceed?
Please adjust the following properties from

ISO Catalog Number

ANSI Catalog Number

to find similar products.

The following files are available

Please select a file to download


You should be logged to see your dashboard information
Session expired due to inactivity, please login again
The product/s () you were trying to add to the cart is/are not available, please contact customer service
item(s) successfully added to the cart
View Cart

. Please enter the desired qty for the material(s) you want to include in your promotion or Proceed Without Promotion and only your base materials will be added to the cart.

Minimum quantity should be

SAP Material Number ISO Catalog Number Grade    

Thank you for your registration, pending approval & completion of the registration, your access is currently limited. Full utilization of product search capabilities & collaboration space is available and will remain. Please allow 2 business days for registration completion.

Thank you for your successful registration. You now have immediate access to log in and utilize the site.

You are about to leave the Solution building process.

Are you sure you want to leave?