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15 Types of Milling Operations

picture of Kat de Naoum
Written by
Aaron Lichtig
Updated by
 7 min read
Published November 22, 2023
Updated September 10, 2024

A brief overview of the most popular milling processes used in manufacturing.

Milling in operation. Image Credit: Shutterstock.com/Andrei Armiagov

The term “milling” refers to the manufacturing process of using a circular cutting tool on the ends and sides of a material blank to make a finished part. That’s obviously just a very general summation; there are actually around 30 different types of milling operations, 15 of which (the most commonly used ones) we’ll go over in this article. 

Common Milling Types

You’ll find that most milling types are self-explanatory with exactly what they do or how they work in their name, but here’s a little more info on each one.

1. Face Milling

Face milling is beloved in the manufacturing world because it can be used to make accurate and smooth surfaces, even on larger pieces. It can make pockets and steps in metal by flattening the material and smoothing out the top. A face mill has cutting edges on its face, which is the part that looks like a disk, and these cutters work by shaving off material from a workpiece horizontally until it reaches the depth required (this will be preset by you). This image explains how it works:

face milling diagram
Face milling diagram

2. Slot Milling

Slot milling makes slots (like grooves or trenches) in any size with a slot cutter which looks like a circular saw blade. This will cut into the sides of the materials to do the job, but you can also use an end mill that cuts on its side and face. It basically carves out a channel in the material, making things like the slot your keys go into (keyways) and other grooves, like this one:

slot milling

A part made with slot milling

3. End Milling

The tool used in end milling has cutting edges on both its end and sides and can make things like slots, pockets, and contours. This method is very common because it is versatile. It’s a little like a drill bit that can cut straight down (plunging) but it can cut sideways, too. The below diagram will give you an idea of how it works.

Diagram of the end milling process.
End milling diagram

4. Thread Milling

The spiraling threads you find on screws and bolts are made with thread milling. The tool has many cutting edges and is able to make threads in many different materials, in all different sizes, and can even tackle more complex designs. The thread milling cutting tool (which, by the way, is known for its durability and accuracy) rotates around the material along the thread path to cut the threads. Its capabilities are pretty much limited to making threads, but it does make them exceedingly well. Here’s a picture of a thread made by thread milling:

thread milling

Thread milling.

5. Shoulder Milling

Shoulder milling removes material from the side of a workpiece (the “shoulder” or “sidewall”) with different cutting tools, like end mills, to make flat, 90-degree angles, like steps.

6. Side Milling

A side milling cutter or end mill is used in side milling to shave thin layers of material from the side of a workpiece. This is the way to go for flat or contoured surfaces. Xometry’s very own Aaron (our marketing SVP) explains more about this milling process in the below video.

7. Profile Milling

If you have to make complex shapes and profiles on a surface, profile milling will be your best friend. It uses a tool with multiple cutting edges to make curves and angles and also has a ball tip that moves around, smoothing everything out. It sometimes (but not always) uses multiple axes to make the cuts. Getting an axis to cooperate in manual milling is, putting it mildly, impossible, so the process often is used with CNC (computer numerical control) machines. Profile milling is used to make dies, molds, and other parts with more detailed surfaces, like this:

A profile milled part from Xometry

Profile milling

8. Saw Milling

Saw milling works with a large, thin, and round cutting tool that has lots of teeth (like a circular saw blade). This fairly quick and easy process is also known as “slitting” because it makes thin slits in a material. The blade of the tool can cut straight down in a vertical line or move along the surface for different types of cuts. 

9. CAM Milling

CAM (computer-aided manufacturing) milling can make parts that most humans would find impossible to create by hand. It’s an automated process, with the cutting tool being controlled by a computer. Human effort is only needed to design the digital blueprint for the part with exact instructions on how to make it in the language that it can understand (don’t worry, there are tools for this) and then feeding it to the computer and switching it on.

10. Gear Milling

As you may have guessed, this milling method has been specifically designed to make gears and gear teeth (like the toothed wheels found in car engines or clocks). It’s done with gear hobbing cutters, or milling cutters, which remove material to make the gear teeth. For simple gears, manual machines are used, but for complex ones, manufacturers tend to go the CNC route.

11. Angle Milling

Angle milling makes beveled edges and angled features on parts. You can use specialized tools with this process, like tapered milling cutters that are cone-shaped or parallel-faced cutters that are flat but can be adjusted at a tilt to get the angle. To get the right tilt, you’d have to use a tilting arbor or four (or more) axis machine.

12. Form Milling

Form milling makes contoured and detailed shapes on a surface with either a specialized milling cutter in the exact shape or profile you want or generic cutting tools (the latter is a somewhat repetitive process, similar to profile milling). It’s used a lot in automotive, aerospace, and mold-making, and many times with a CNC machine.

13. Straddle Milling

Straddle milling involves mounting two milling cutters on an arbor and positioning them next to each other to create parallel slots, grooves, or surfaces on your chosen material. Because it has two cutting tools, it can essentially finish a piece in half the time. We see this process used often for keyway milling and machining flats on opposite sides of a shaft.

14. Plain Milling

It might not have a very interesting name, but plain milling is still a useful manufacturing method. It’s pretty basic, removing material from a surface using a flat, horizontal cutting tool, and it is used for making square or rectangular features. Here’s what that looks like:

Plain milling
Plain milling diagram

15. Gang Milling

Gang milling is a little more aggressive, requiring you to mount several cutters on a single arbor. This allows you to cut multiple surfaces or features using a single pass. This is a good method to use if you want to keep productivity high and not have to spend lots of time setting up and handling several individual machines. It’s great for mass production of identical parts, but would be overkill for low-volume needs.

Summary

To make things super simple, here’s a useful cut-out-and-keep, quick-reference guide on the different milling types.

Milling TypeCutting ToolApplications
Milling Type
Face
Cutting Tool
Cutters on its face
Applications
Flat surfaces, pockets
Milling Type
Slot
Cutting Tool
End mill or slot cutter
Applications
Slots, grooves
Milling Type
End
Cutting Tool
Cutters on edges and sides
Applications
Slots, pockets, contours
Milling Type
Thread
Cutting Tool
Multiple cutting edges
Applications
Internal/external threads
Milling Type
Shoulder
Cutting Tool
Various cutters (i.e., end mills)
Applications
Flat, 90-degree shoulders, step features
Milling Type
Side
Cutting Tool
End mill or side mill cutter
Applications
Slots, grooves, pickets
Milling Type
Profile
Cutting Tool
Multiple cutting edges and ball tip to smoothen
Applications
Intricate shapes and profiles
Milling Type
Saw
Cutting Tool
Narrow, large-diameter with many teeth
Applications
Slots, grooves, profiles
Milling Type
CAM
Cutting Tool
Any via automation
Applications
Any and all
Milling Type
Gear
Cutting Tool
Gear hobbing cutters, milling cutters
Applications
Gears, gear teeth
Milling Type
Angle
Cutting Tool
Tapered milling cutters, parallel-faced cutters
Applications
Beveled edges, chamfers, angles
Milling Type
Form
Cutting Tool
Custom-made to the shape you want to create
Applications
Contoured and detailed shapes in automotive, aerospace, mold-making
Milling Type
Straddle
Cutting Tool
Two parallel cutters
Applications
Parallel slots or grooves
Milling Type
Plain
Cutting Tool
Flat, horizontal cutter
Applications
Square/rectangular features
Milling Type
Gang
Cutting Tool
Many cutters on a single arbor
Applications
Quick, for mass produced parts

Tools and Applications for Different Milling Types

How Xometry Can Help

Xometry provides a wide range of manufacturing capabilities, including all the types of milling mentioned in this article, as well as 3D printing, laser cutting, CNC machining, and much more. If you want to learn more about machining or request a free no-obligation quote, reach out to a Xometry representative today.

Disclaimer

The content appearing on this webpage is for informational purposes only. Xometry makes no representation or warranty of any kind, be it expressed or implied, as to the accuracy, completeness, or validity of the information. Any performance parameters, geometric tolerances, specific design features, quality and types of materials, or processes should not be inferred to represent what will be delivered by third-party suppliers or manufacturers through Xometry’s network. Buyers seeking quotes for parts are responsible for defining the specific requirements for those parts. Please refer to our terms and conditions for more information.

picture of Kat de Naoum
Kat de Naoum
Kat de Naoum is a writer, author, editor, and content specialist from the UK with 20+ years of writing experience. Kat has experience writing for a variety of manufacturing and technical organizations and loves the world of engineering. Alongside writing, Kat was a paralegal for almost 10 years, seven of which were in ship finance. She has written for many publications, both print and online. Kat has a BA in English literature and philosophy, and an MA in creative writing from Kingston University.

Read more articles by Kat de Naoum

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