Turning-friendly geometry.
Round about axis
Turned parts are inherently axially symmetric. Features must be on or about rotation axis. Off-axis features need secondary milling operation.
Keep L/D < 4
Long thin shafts deflect during cutting. L/D > 4: requires steady rest support. L/D > 8: Swiss machine territory.
Tool clearance
Undercuts (grooves narrower at top) require specialty tooling. Add chamfer or relief instead when possible.
Standard preferred
Standard metric (M3-M50) and inch (UNC, UNF) threads cheapest. Custom thread pitches require specialty tools.
Stepped shaft design.
Step transition radius
Generous fillet at diameter changes. Reduces stress concentration.
Tool relief width
Allow 5× tool width for tool to enter relief without gouging.
Different Ra OK
Different surface finish on different zones is fine — bearing journals smooth, OD areas standard.
±0.01 mm typical
Concentricity between turned features achievable to ±0.01 mm without specialty processes.
Specify pattern
Diamond, straight, or angle knurl available. Common widths 5-25 mm.
For grinding
Center drill at ends if subsequent grinding planned.
Threading on lathe.
Single-point threading: precision and any custom pitch. Slower than die threading. Ideal for precision threads on shafts > 25mm diameter.
Die threading (chasers): faster, repeatable. Limited to standard pitches. Most production threads cut this way.
Thread relief: always specify thread relief at thread end. Allows tool runout, ensures full thread depth.
Class 2A/2B: default for most production. Class 3A/3B for precision applications (aerospace, instruments).
Combined turning + milling.
Live tooling enables
Pure turning when
FAQ
L/D up to 4 standard turning. L/D 4-8 with steady rest. L/D > 8 requires Swiss-type lathe with sliding headstock and guide bushing.
Threading on lathe (single point or die): for external threads or large internal threads. Tapping: for internal threads up to about M16 in production. Choose based on size and thread quality.
Standard Ra 0.8-1.6 µm. Fine turning Ra 0.4 µm. Polished finish Ra 0.1 µm with subsequent operation. Specify per function.
Roundness ±0.005 mm achievable on quality lathes with proper tooling. Sub-µm requires grinding or precision lapping.
Live tooling adds 10-25% to standard turning operation cost. Saves significantly vs separate milling setup. Net win for parts needing both turning and milling features.
Yes — bar feed enables unattended production runs. Standard for production volumes 200+. Adds setup time but dramatically reduces per-part cost.
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