What is CNC Turning?

CNC turning is a subtractive process in which material is removed from a workpiece as it’s shaped into various components. Machining processes sometimes utilize a cutter that moves along the workpiece. And sometimes the workpiece itself is mobile while the cutting tool remains stationary. CNC turning is of the latter persuasion. In this way, CNC turning is a reverse process, in contrast to milling and the other disciplines that involve an immobile workpiece.

A turning center or lathe can quickly fashion many pieces, made from the same chunk of material (or not), in a short amount of time. Compared to other often-used fabrication methods, turning is generally preferred with less complex shapes, while the more intricate geometries are delegated to other processes such as milling or electric discharge machining.  

Cutting Equations: How Are RPM and Feed Rate Calculated?

Cutting speed is an important metric and is recorded in surface feet per minute, or SFM. This measure is analogous to the miles per hour figure offered by your car’s speedometer. Just like mph, it’s a linear measure of distance traveled, though in this case, it’s the distance traveled by a cutting tool. 

SFM even scales to mph, with 300 SFM converting to an underwhelming 3.4 mph. Different materials benefit from various cutting speeds, so it’s essential to work accordingly. The rotational frequency in revolutions per minute (rpm) can be ascertained through a simple formula:

Rpm = sfm ÷ diameter of cutting tool × 3.82

Feed rate measures how much the cutter is being fed. Or the rate at which it is altering the workpiece, in terms of distance (millimeters or inches) per revolution. Feed rate depends on many factors, including the machine, the material, the power available at the spindle, the finish, and the cut desired, among other factors.

This is no problem—the convenience and uncompromising precision of CNC capabilities remove the engineers' onus for personally considering all these aspects. All the while offering the proven benefits of CNC manufacture, including efficient output, improved safety, reduced time to market, decreased costs, and minimized error rates. 

And as AI and CAD (computer-aided design) technologies improve, machines will only become more intuitive and better able to learn from an influx of more extensive data.

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