CNC Turning Milling Drilling Grinding

You open the shop door: the steady hum of a lathe, the clack of a milling cutter, the metallic smell of coolant, and a freshly ground part catching the overhead light. A procurement manager hands you a drawing with tight fits, a stack of prototypes, and a deadline - which process should you pick to meet tolerance, cost, and lead time? This guide helps you make that decision and turn the result into a high-performing Google page that ranks.

Quick summary: when to use each process

Turning: best for cylindrical parts, shafts, bushings; fast single-op cycles. Typical tolerances: ±0.02–0.005 mm (depending on finish/fixture).

Milling: best for complex flats, slots, pockets, 3D contours; flexible for prototypes and low–medium volumes. Typical tolerances: ±0.05–0.01 mm.

Drilling: holes and basic bores; use reaming or boring for precision holes. Typical hole tolerance: H7 / ±0.01–0.02 mm after reaming.

Grinding: final-size accuracy and fine surface finish (mirror finishes, ∼Ra 0.1–0.4 μm); used for hardened materials and shrink-fit shafts.

(Use the process or combination - e.g., turn→mill→grind - depending on geometry and required finish.)

H2 - Process selection checklist

Geometry: cylindrical → turning; prismatic/complex surfaces → milling.

Material hardness >40 HRC → consider grinding or hard milling.

Hole accuracy >0.01 mm → drill → ream/boring → hone/finish.

Volume: prototyping → flexible milling/turn-mill; high volume → dedicated turning or multi-op machining.

Surface finish: Ra < 0.4 μm → grinding or superfinishing.

H2 - Cost drivers & quoting points 

Break down the quote into:

Setup time (CAM, fixturing) - dominates low-volume quotes.

Cycle time - toolpath strategy, feeds/speeds, and automation.

Material cost - exotic alloys raise machining time and tool wear.

Secondary ops - heat treatment, grinding, coating, inspection.

Tolerance & inspection - CMM time, SPC adds cost.

Practical tip: show a sample quote table on your page (itemized) to satisfy "Buy" intent: tooling, raw material, process time, secondary ops, lead time, MOQ.

H2 - Example (illustrative) case study - prototype → production

Illustrative results (example only):

Problem: 100 mm shaft, Ø tolerance ±0.01 mm, Ra 0.8 μm, 500 pcs/month.

Solution: rough turning + finish grinding.

Outcome: cycle time per piece 90s turning + 45s grinding; scrap rate reduced from 4% to 0.6% after process optimization; unit cost dropped 18% when switching to CNC turn-grind cell for production.

Label this block as an illustrative example so readers understand the numbers are representative industry outcomes, not a claim of personal testing.

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