CNC Milling vs. Turning: What You Can Use For Creating Your Product?

You’ve got a component to create and have already designed the perfect CAD drawings. Now it’s time for the hardest part of the manufacturing process—the machining phase. If the part needs CNC manufacturing, should the component be milled or turned? Well, that is ultimately determined by the gear and budget available. However, to better understand the two processes, it would be useful to compare them.

There are possibly hundreds of books, manuals, and videos that explain each of these steps, and some, generally the longer ones, solely touch on minor nuances. To keep this article brief and sweet, we’ll merely scratch the surface of CNC milling and turning. So, let’s get started.

What Is CNC Turning?

CNC milling and turning are two popular machining techniques. They’re both subtractive, which means they eliminate surplus stock material to get to the result—your component. Apart from that one essential difference, they are two distinct processes.

CNC turning takes place on a machine known as a lathe, where the material rotates while the tool remains fixed. Typically, the item is kept in position in a spinning spindle by a chuck that can grip with jaws or hydraulics. A turret loaded with a cutting tool travels toward the raw material and extracts it as the object turns, creating the required form. The turret’s tools are quite stiff, and it rotates to alter which tool contacts with the material. Because the object is rotating as the tools remove material, the resulting shape is a rotated profile: a sphere, a cone, a cylinder—you get the point.

What Is CNC Milling?

There are several machine setups for CNC milling, but usually, the item remains fixed while a cutting tool rotates to carve out the required shape. Clamps or vice are typically used to secure the item to the machine bed. Cutting tools, such as end mills or drills, cut off material to expose the specified section. Imagine a sculptor hastily cutting a sculpture out of a piece of granite, and you get the notion of milling.

Mills come in a variety of combinations that can add complexity and usefulness. Because of their versatility, even basic arrangements bring value. Milling machines easily slice away wood, metal, plastics, and other materials. Most mills have modular or adaptable work holding, and it’s typical to make bespoke vise jaws on the very same machine that will ultimately cut the item.

Should You Mill First, Then Turn?

From a geometric standpoint, you will most likely turn before milling. A milling machine can grip a circular item more easily than a revolving chuck or lathe can. However, there are soft jaws for rotating chucks that can accommodate complicated forms, therefore milling first and turning second is not difficult. Typically, these process decisions are influenced by part requirements, such as which features require the highest precision. Shifting a part from one machine to another reduces precision from feature to feature, so location and final part requirements must be considered.

What Are The Pros And Cons Of Milling And Turning?

If you only have a 2-axis lathe, you’re limited to round pieces. When turning bits or inserts degrade, the procedure of replacing them in the turret is extremely laborious, as a result, production is halted until maintenance can be performed. Metal chips that shatter into the tool rather than against themselves might harm the blade or the machine. When your machines are running 24 hours a day, there is an art to checking chips.

Most milling tools enable you to simply replace tools and monitor wear. When changing tools, a tool probe may be used to execute wear adjustment data and breakage tests only with a few coding. If a tool has to be replaced, it’s quite straightforward to automate the machine to replace it without missing a beat.

Despite their versatility, milling machines fall short in a few areas. Any square interior corner within two vertical surfaces requires post-processing. Tall walls necessitate equally long tools, which might deflect greatly, resulting in a poor surface quality that must be finished manually or in a different arrangement.

It’s a good idea to build filets for milling and turning to maintain your machine action smooth and to avoid forcing a tool into a corner. Jittery tool motion and abrupt increases in engagement can cause wear and fracture, causing the entire operation to be disrupted. Filets aid in the smooth movement of the machine between features, resulting in a smoother surface and more uniform stresses on the tool.

Final Thoughts

As we mentioned, there is much to learn and implement in any machining process. Considerations include your machine’s capabilities, the resources you have, and the things you want to create. Comparing milling to turning felt like comparing apples to oranges. Although they are both subtractive processes, the specifics are vastly different. Hopefully, looking at those distinctions and contemplating how each might affect the process of machining a finished product was a pleasant exercise.

Photo by Daniel Smyth on Unsplash