What is the main difference between CNC turning parts and CNC milling parts?

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The fundamental difference is motion: CNC turning rotates the workpiece on a spindle while a stationary cutting tool shapes it, producing round, symmetrical parts like shafts and bushings. CNC milling rotates the cutting tool against a stationary workpiece, creating complex 3D geometries like pockets, slots, and contoured surfaces. Many parts require both processes.

CNC Turning Explained

In CNC turning, the workpiece is held in a chuck and rotated at high speed (typically 1,000-6,000 RPM). The cutting tool moves linearly along X and Z axes to remove material. This process is ideal for cylindrical parts: shafts, rods, bushings, pulleys, and threaded components. CNC turning centers with live tooling can also perform milling operations, drilling, and tapping in a single setup. Typical tolerances: ±0.0005".

CNC Milling Explained

In CNC milling, the workpiece remains stationary on the machine table while rotating cutting tools move along multiple axes (3-axis, 4-axis, or 5-axis) to remove material. Milling can produce flat surfaces, pockets, slots, threads, undercuts, and complex 3D contours. It is the preferred process for brackets, enclosures, engine blocks, molds, and complex structural components. Typical tolerances: ±0.001".

Choosing Between Them

Choose turning when your part is primarily cylindrical with features concentric to the center axis. Choose milling when your part has flat surfaces, complex contours, or features on multiple faces. Many parts use both -- a turned blank that then goes to a milling machine for secondary features. SOMI offers both processes and can handle combined turning + milling in a single setup using live-tooling CNC lathes.

Why Choose SOMI Custom Parts

At SOMI Custom Parts, we maintain separate turning and milling departments with over 50 CNC machines. Our engineering team helps you determine the most efficient process for each part -- and often combines both to optimize cost and quality. We also offer turn-mill centers that complete both turning and milling in a single setup, reducing lead times and eliminating fixturing errors.

Case Study

A hydraulic equipment manufacturer needed a valve body requiring both cylindrical turning and complex pocket milling. A single-source approach allowed SOMI to complete the turning on a CNC lathe, then transfer to a 4-axis milling center for the pockets and port threading. By coordinating both processes internally, SOMI delivered 1,000 units in 3 weeks with zero inter-process quality issues.

Industry Data

According to Gardner Business Media's 2025 Metalworking Survey, approximately 35% of CNC machine tools worldwide are lathes (turning) and 55% are machining centers (milling). The remaining 10% are specialized machines like EDM and grinding. Parts requiring both turning and milling represent 40% of all precision machining work.