WhatisCNCTurning?
Rotationally symmetric precision parts — from shafts to flanges.
Turning — Definition and Principle
CNC turning is a subtractive manufacturing process in which the workpiece rotates and a stationary or driven tool removes material in the form of chips. It is the standard process for rotationally symmetric components such as shafts, bolts, bushings, flanges, and threaded studs.
In CNC turning, the workpiece is fixed in a chuck (for chuck parts) or between centers (for long shafts) and rotated at defined speeds. The tool traces defined contours — controlled by the CNC program.
Turning Processes in Detail
| Process | Description | Typical Application |
|---|---|---|
| Longitudinal turning | Tool moves parallel to the rotation axis | Outside diameters, shaft steps |
| Face turning | Tool moves radially | End faces, flat surfaces |
| Grooving | Tool plunges radially | Grooves, undercuts, relief cuts |
| Thread turning | Synchronized spindle and feed movement | External and internal threads |
| Internal turning (boring) | Machining internal contours | Bores, fits |
| Parting off | Separating the finished part from bar stock | Serial parts with bar feeder |
Bar Feeder — Automated Series Production
For batches of ~20+ pieces, we use a bar feeder:
- Bar stock (up to Ø32 mm for short/long turned parts, up to Ø65 mm in the NLX 2000 bar feeder) is automatically fed
- The machine operates unattended — including nights and weekends
- Significantly lower unit costs for small and medium batches
- Typical cycle: machining → parting off → next part — fully automated
Live Tooling — Turning and Milling in One
Modern CNC lathes feature live tools on the turret: small milling or drilling units that can work perpendicular to the turning axis. This enables:
- Cross-holes without re-clamping
- Flats and slots on turned parts
- Hexagonal contours and wrench flats
- Threads on end faces
Result: complete machining in a single setup — shorter lead times, higher accuracy, lower costs.
Typical Materials and Tolerances
CNC turning is possible with all machinable materials:
- Free-machining steel (11SMnPb30) — Ideal turning material, short-breaking chips
- Structural steel (S235, S355) — Universal, good machinability
- Stainless steel (1.4301, 1.4571) — Requires sharp tools and optimized cutting data
- Aluminum (6082, 7075) — High spindle speeds possible, excellent surface finish
- Brass, Bronze — Outstanding machinability, shiny surfaces
Standard tolerances in CNC turning: ±0.02 mm. For fits (H7, g6, f7) we achieve ±0.005 mm with subsequent measurement of every part.
Frequently Asked Questions
What is the difference between turning and milling?
In turning, the workpiece rotates and the tool is stationary or moves linearly. In milling, the tool rotates and the workpiece is stationary. Turning is suited for round parts (shafts, bolts), milling for prismatic parts (housings, plates).
What is a bar feeder?
A bar feeder is an automatic feeding device for CNC lathes. Bar stock is automatically advanced, allowing serial parts to be manufactured without manual intervention.
What tolerances does CNC turning achieve?
Standard: ±0.02 mm. For fits (H7, g6, f7): ±0.005 mm is possible. The achievable tolerance depends on material, diameter, and length.
What is the maximum diameter for CNC turning?
At Strobel Industry, we turn up to Ø250 mm (chuck parts on the NLX 2000) and up to Ø32 mm on the Traub TNL 32 in short/long turning mode. The bar feeder accommodates up to Ø65 mm.
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