Turning, mill-turn, and when to choose which

CNC turning rotates the workpiece while a cutting tool moves in X (radial) and Z (axial) directions — producing cylindrical features like shafts, bushings, and flanges. Our lathes add Y-axis and live-tool spindles, meaning a rotating cutter can mill flats, cross-holes, slots, and threads on the side of a turned part without re-fixturing.

This matters for two reasons. First, every setup introduces alignment error; mill-turn eliminates setup-to-setup errors entirely. Second, every setup takes labor — a mill-turned part might have 6 operations completed in 2 minutes of cycle time, where a two-machine process (turn then mill) would take 8 minutes plus fixture work.

Shaft length limits

Long slender shafts (length-to-diameter ratio above 10:1) require tailstock support or steady rest to prevent deflection. For ratios above 20:1, consider Swiss-type turning — the guide bushing supports the bar right at the cutting point, enabling ratios up to 40:1.

§ 01 / Equipment

Machines currently in operation.

Machine Capacity Spindle / Capability Qty Typical use
Nakamura-Tome WT-150IIØ300 × 600 mm · Y-axis · dual spindle6,000 rpm · live tool 6,000 rpm3Mill-turn production, small-medium complex parts
Doosan Puma 2600SYØ420 × 1000 mm · Y-axis · sub-spindle4,500 rpm · live tool 6,000 rpm2Larger mill-turn work, aerospace shafts
Doosan Puma 400LBØ420 × 1500 mm3,500 rpm2Long shafts, large flanges, non-complex turning
Haas ST-20YØ305 × 533 mm · Y-axis4,000 rpm · live tool2Small to medium prototype mill-turn work
Haas ST-10Ø203 × 356 mm6,000 rpm2Small-diameter production turning
§ 02 / Applications

Parts we make most often with this process.

CATEGORY · FLUID POWER

Shafts & pistons

Hydraulic cylinder rods, pump shafts, valve spools. Usually 4140 steel or 17-4 PH stainless, ground to Ra 0.4 μm on critical diameters.

CATEGORY · CONNECTORS

Threaded fittings

NPT, BSPP, JIC hydraulic fittings, RF connector bodies. Brass C360 for fluid fittings, tin-plated brass or nickel-plated aluminum for RF.

CATEGORY · AEROSPACE

Bushings & spacers

Tight-tolerance bushings for aircraft assembly, precision spacers for optical systems. Usually steel or titanium, with ground ID for bearing fits.

CATEGORY · MEDICAL

Surgical shafts

Instrument shafts, trocars, drill guides. Titanium Gr 5 or Gr 23 ELI, passivated to ASTM F86, often PVD-coated.

CATEGORY · ROBOTICS

Ball screw components

Custom ball screw ends, threaded shafts, gear shaft blanks. Pre-hardened 4140 or through-hardened for final grinding.

CATEGORY · CONSUMER

Custom hardware

Knobs, thumbscrews, cam-lock mechanisms, product hardware. Often aluminum with anodized finish, or brass/stainless for premium feel.

§ 03 / Design considerations

What to know before releasing a drawing.

01
Avoid deep narrow grooves
Grooving tools are fragile and expensive. A groove deeper than 1.5× its width significantly increases cost. If you need a sealing groove (O-ring), use standard dimensions from your o-ring supplier's groove tables — they're chosen to work with stock grooving inserts.
02
Corner radii at shoulder transitions
Specify a corner radius (minimum 0.5 mm) at every diameter transition. A sharp 90° shoulder requires a separate operation with a profile tool and creates a stress concentration. If your mating part demands a sharp corner, add a relief groove instead.
03
Thread relief grooves
Threads that run right up to a shoulder are impossible — the tap or threading tool needs runoff space. Provide a relief groove (typically 1× thread pitch wide) at the thread end, or specify 'thread to full depth per drawing' and let us add the relief.
04
Length-to-diameter ratios
Shafts above 10:1 L:D ratio require tailstock support. Above 20:1, switch to Swiss turning. Above 30:1, consider multi-piece assembly with a bonded joint — not every shaft has to be one piece of material.
05
Knurling and decorative features
Knurled grips add ~$2–$5 per piece (extra operation) but dramatically improve hand-feel on adjustment knobs. Diamond knurls are standard; straight knurls cost slightly less. Specify depth with the knurl type (e.g., 'medium diamond knurl, 0.5 mm depth').

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