Posted June 2, 2021

Turning vs. Milling: What's the Difference?

A CNC lathe machine slot cutting by the milling turret

The tools for machining parts have a long history of service, from their manually operated origins to DIY shops. Industrial manufacturing also uses them extensively, where computer numeric control systems drive them. CNC machining employs two primary pieces of equipment: lathes and mills. This article will explore the differences between turning vs. milling. 

Turning: Machining a Part with a Lathe

A lathe forms a block of material known as a workpiece into the desired shape. It allows operators to remove material from it using various cutting, shaving, or sanding tools while spinning the workpiece rapidly. Lathes vary in size from the small machines jeweler’s use to the large automated types for industrial manufacturing.

The first known evidence of creating a product with a lathe is a wooden bowl found from the 6th century BC. Early lathes were simple and required two people for their operation; one to turn the material with a rope and another to shape it with a cutting tool. Incremental improvements were made to lathes beginning with a pedal for the operator to turn the workpiece. During the industrial revolution, parts were fabricated for other machine tools by lathes using water wheels and steam engines for power. Electric motors had been introduced to power lathes by the beginning of the 20th century, and improvements in control and precision continue to this day.

Products can be turned on a lathe using almost any material. However, specialized lathes make items such as glasswork, ornamental products, or small precision parts in watches. A lathe has a bed which is typically a horizontal beam, with the spindle to turn the workpiece (typically on the left side). Mounted to the spindle is a chuck that holds the workpiece in place so that the different tools on the tool post can cut it. With this configuration, the lathe removes material from the spinning workpiece. This process is nearly opposite to that of a milling machine.

Machining a Part on a Mill: Turning vs. Milling

A milling machine removes material from a workpiece with a rotary tool like a drill-bit spinning at high speed. The mill moves the cutting tool in one or more axes to create the desired shape and contours of parts made of various solid materials such as metal, wood, and plastic.

Originally developed to assist with filing parts down by hand, the capabilities of milling machines have grown throughout the years just as lathes have. Eli Whitney—who is better known for inventing the cotton gin—designed the milling machine over 200 years ago to mass-produce gun parts. Later milling machine improvements saw innovations in cutting tools and power. By World War II, mills were available that could slide and pivot, giving users the ability to work from any angle. In addition, milling machines now incorporate servomechanisms that precisely move the tool head and the workpiece improving quality and reducing production time.

Milling machines perform multiple fabrication functions, including cutting slots, routing, drilling, and threading, employing different types of tools for each process. These tools include mill ends, drill bits, thread mills, reamers, and hollow mills, which spin at high speed in a spindle set by the operator. The spindle and the motor comprise one sub-assembly that positions the tool over the workpiece, held in place on the worktable by a fixture.

Lathes and mills both remove material from a workpiece in a process known as subtractive manufacturing. The machines do this very differently, however, and manufacturers sum up the difference between the two like this:

  • A lathe spins or turns the workpiece so that a stationary cutting tool can remove material. 
  • A mill spins a rotary cutting tool to remove material from a workpiece held in place on the worktable.

For a long time, manufacturers have relied on these fabrication processes to produce parts across numerous industries. With the addition of CNC technology back in the 1960s, turning and milling parts has become the standard for manufacturing precision parts and essential now more than ever before.

Modernizing Turning and Milling with Computer Numeric Control (CNC) Systems

Running lathes and mills by hand not only takes an incredible amount of skill on the part of the operator, but it was hazardous to move the cutting tools and workpieces manually. With the introduction of the early pre-programmed lathes and mills, automated control of the moving tools and workpieces resolved the safety issues. As computer systems increased in their abilities, the precision of the lathes and mills improved as well. With CNC technology, lathes and mills could produce the tight tolerances required for aerospace and other precision parts.

Now, advanced CNC turning and milling machines work together with advanced software that not only calculates the best cutting paths but continually learns with each successive project. As a result, these systems constantly improve their performance to reduce the time needed for manufacturing and save the customer money while improving precision and quality.

At Plethora, we specialize in manufacturing precision parts using the industry's most advanced CNC machining equipment and software. Our smart factory systems go to work when you upload your CAD files to us, as our design for manufacturing (DFM) system analyzes it and prepares it for fabrication. Simultaneously, our production team will collaborate with you to ensure that we build your part according to the original design intent. We are ISO 9001 certified, supporting our primary goal of manufacturing parts to the highest level of quality. Our online DFM and quoting systems are ready to receive your data and begin working on your next project. To get started, upload your design files to Quote My Part or call us at 415-726-2256.

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The Plethora Team

The Plethora team is your go-to CNC manufacturer for hardware done right the first time. We have the tools and experience needed to create high quality custom parts quickly and with precision, whether you need a prototype or production run.

Topics: materials, finishing, CNC machining, CNC milling

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