Turning

Turning machines rotationally symmetric parts on a lathe, delivering accurate diameters, faces, and threads efficiently from bar or chuck stock.

Overview

Turning is a machining process where a cutting tool removes material from a rotating workpiece, typically on a CNC lathe or manual lathe. It excels at producing accurate diameters, shoulders, grooves, bores, and threads on shafts, bushings, and other round parts. Variants like 2-axis turning, mill-turn with live tooling, Swiss turning, and multi-spindle lathes cover everything from prototype shafts to high-volume precision pins.

Use turning when your part is primarily cylindrical, needs good concentricity between features, and you want repeatable tolerances at reasonable cost. It handles most metals and plastics efficiently, especially from bar stock. The tradeoffs: complex non-round geometry often requires secondary milling, very long slender parts may need special support, and ultra-tight tolerance/finish zones might require grinding after turning. For many rotational parts, though, a well-set-up turning process offers the best balance of speed, cost, and precision.

Common Materials

  • Aluminum 6061
  • Steel 1018
  • Stainless 304
  • Brass C360
  • Titanium Grade 5

Tolerances

±0.001" to ±0.003"

Applications

  • Transmission shafts
  • Bushings and spacers
  • Pins and dowels
  • Threaded fittings and fasteners
  • Hydraulic and pneumatic cylinders
  • Pulleys and rollers

When to Choose Turning

Choose turning when the part is primarily round, with critical diameters, bores, or threads that must be concentric. It is ideal from prototypes to high-volume production using bar or chucking work. Parts with a clear centerline and mostly rotational features benefit most from this process.

vs Milling

Pick turning when the part is dominated by cylindrical features around a single axis and needs tight concentricity between diameters, bores, and threads. Lathes remove material more efficiently for round parts, often reducing cycle time and improving surface finish compared to milling circular profiles.

vs Drilling

Choose turning when you need accurate outside diameters, faces, and multiple concentric features in addition to holes. Drilling alone handles straight holes, but turning controls OD, ID, and shoulders in one setup, improving runout and feature relationships.

vs Grinding

Use turning when tolerances and surface finish can be met economically without going to sub-thousandths and mirror finishes. Turning is faster and cheaper for most general tolerance shafts and bushings; reserve grinding for only the tightest diameter or roundness requirements.

vs Electrical Discharge Machining (EDM)

Select turning for rotational parts where you want fast cycle times and lower cost on common metals, rather than intricate shapes or very hard materials that truly need EDM. For simple round profiles and threads, turning beats EDM in throughput and price.

vs Broaching

Choose turning when splines, keyways, or internal forms are not the only defining features, or when volume does not justify dedicated broach tooling. Lathes efficiently create the basic cylindrical geometry and many features, with broaching reserved as a secondary step only if specific internal profiles are required.

Design Considerations

  • Keep parts primarily rotational with clear centerlines; avoid unnecessary flats or complex non-round geometry that drive secondary milling operations
  • Limit length-to-diameter ratio or plan for centers/steady rests; very slender parts chatter and require slower, more expensive setups
  • Specify realistic tolerances and surface finishes only where functionally needed; blanket tight callouts increase cycle time and inspection cost
  • Standardize thread sizes, chamfers, and groove profiles so shops can use off-the-shelf tooling and gages
  • Use generous fillet radii and avoid sharp internal corners to improve tool life and chip evacuation
  • Clearly define datum structure on key diameters and faces to communicate concentricity and runout requirements unambiguously