Metal Machining: Processes, Materials & Tolerances
The subtractive processes that turn metal stock into precision parts — milling, turning, drilling, grinding, EDM — with the tolerances, finishes, and materials that define each.
IsoCNC Engineering Team
CNC Machining & DFM Engineers · Updated · 6 min read
On this page
Quick Answer
Metal machining removes material from a metal workpiece to create a finished part. The main processes are milling, turning, drilling, grinding, and EDM — each with its own tolerance and finish: milling ±0.05–0.1 mm, turning ±0.025–0.05 mm, grinding ±0.002–0.005 mm. The metals are aluminum, steel, stainless, titanium, and brass, and the industries span aerospace, automotive, medical, and industrial equipment.
The Umbrella Term for Cutting Metal
Metal machining is subtractive manufacturing — you start with a block, bar, or billet of metal and remove material until only the final shape remains. It is the umbrella term covering milling, turning, drilling, grinding, and EDM, and it is how the vast majority of precision mechanical parts get made, from a bracket to a shaft to an engine component. Understanding the processes — and which one your part needs — is the first step to a good quote. Our what is CNC machining guide covers the fundamentals.
The Five Processes at a Glance
Each process has a tolerance and finish envelope:
| Process | Typical tolerance | Surface finish (Ra) | Use |
|---|---|---|---|
| Milling | ±0.05–0.1 mm | 1.6–3.2 µm | Flats, slots, pockets, 3D shapes |
| Turning | ±0.025–0.05 mm | 0.8–1.6 µm | Shafts, bushings, threaded parts |
| Drilling | Looser (unless post-processed) | — | Round holes |
| Grinding | ±0.002–0.005 mm | 0.2–0.8 µm | Precision, hardened parts |
| EDM | ±0.005–0.01 mm | Fine | Intricate geometry, hard materials |
The pattern: milling and turning are the workhorses for general parts, drilling makes holes, and grinding and EDM are reserved for the highest precision or special geometry. Our CNC grinding guide and reaming guide cover the precision end in depth.
Our Machining Capabilities
Every metal machining process, on its own page:
CNC milling — flats, slots, pockets, and complex 3D shapes.
CNC turning — shafts, bushings, and threaded cylindrical parts.
5-axis machining — complex geometry in one setup.
Swiss machining — small, precise turned parts.
Production machining — volume runs.
For the metals themselves, see our materials hub and metal materials guide.
Where Metal Machining Is Used
Aerospace — structural parts, brackets, housings, precision components.
Automotive — engine, drivetrain, and transmission components.
Medical — surgical tools, device parts, implants, instrument components.
Industrial equipment — machine parts, tooling, wear components.
Electronics and energy — enclosures, heat sinks, fittings, valves, pumps.
FAQ
What is metal machining?
Metal machining is a subtractive manufacturing process that removes material from a metal workpiece to create a final shape, size, and surface finish. It is the umbrella term for operations like milling, turning, drilling, grinding, and EDM. Metal machining is how most precision mechanical parts — from brackets to shafts to engine components — get made.
What are the main metal machining processes?
Five core processes. Milling uses a rotating cutter for flats, slots, pockets, and complex 3D shapes. Turning rotates the workpiece against a tool for cylindrical parts like shafts and bushings. Drilling creates round holes (often followed by reaming or boring for tighter quality). Grinding uses an abrasive wheel for precision and hardened parts. EDM removes material with spark erosion for intricate geometry and hard materials. Our CNC grinding and reaming guides cover the finishing end in detail.
What metals can be machined?
The workhorses are aluminum (lightweight parts and housings), steel (structural and wear-resistant parts), stainless steel (corrosion resistance and strength), titanium (high strength-to-weight), and brass (fittings, connectors, and precision components). Each machines differently — aluminum cuts fast, titanium and stainless are slower and harder on tools. Our materials hub and metal materials guide map the full selection.
What tolerances does metal machining achieve?
It depends on the process. Milling typically holds ±0.05–0.1 mm, turning ±0.025–0.05 mm, grinding ±0.002–0.005 mm, and EDM ±0.005–0.01 mm. In short, standard CNC machining delivers tight, production-ready tolerances, while grinding and EDM are reserved for the highest precision or special geometry. Our tolerances guide covers the full picture.
What surface finish does metal machining produce?
Milling lands around Ra 1.6–3.2 µm, turning around Ra 0.8–1.6 µm, and grinding can reach Ra 0.2–0.8 µm or finer. The finish you get is set by the process and the roughing-finishing strategy. Our surface finish guide has the full Ra chart.
What industries use metal machining?
Practically every mechanical industry: aerospace (structural parts, brackets, housings), automotive (engine, drivetrain, transmission components), medical (surgical tools, implants, instrument parts), industrial equipment (machine parts, tooling), electronics (enclosures, heat sinks), and energy (fittings, valves, pumps). Our industries hub links to the sector pages.
Related Resources
Custom Machining: Parts Made to Your Drawing
Custom machining explained: custom vs off-the-shelf parts, the CAD-to-inspection process, materials and processes,…
Metal Materials for Machining: How to Choose
Metal materials guide for machined parts: the main families (aluminum, steel, stainless, titanium, copper alloys),…
How to Outsource CNC Machining to China, Step by Step
How to outsource CNC machining to China, step by step: vet suppliers, compare landed cost, control quality remotely,…
Metal Parts, Machined to Spec
IsoCNC machines aluminum, steel, stainless, titanium, and brass daily — milling, turning, 5-axis, and grinding — with CMM inspection and material certs. Send the drawing; an engineer reviews every RFQ, typically within 1–2 business days.