CNC Processing and Production: How a Design Becomes a Shipped Part

• 1
  What CNC processing and production actually removes
• 2
  Setup count drives cost before tolerance does
• 3
  Where the tolerance and finish numbers come from
• 4
  How prototype work scales into production runs
• 5
  Material choice sets the process window
• 6
  Which route fits which part

CNC processing and production is subtractive. A rotating tool with defined edges enters the workpiece along programmed paths and shears away material in chips. Nothing is molded or layered, so the geometry you get is limited by tool reach and fixturing, not by draft angles or wall-thickness rules. That single fact explains most of the cost and tolerance behavior you see on a quote.

Every cut has three numbers attached: surface speed, feed per tooth, and axial depth of cut. Aluminum 6061 might run at 300–500 m/min with a 10 mm carbide end mill, while Ti-6Al-4V drops to 40–60 m/min because titanium conducts heat poorly and work-hardens at the cut edge. Run titanium too fast and the tool edge dulls in minutes.

Chip evacuation is the hidden constraint. A deep pocket that looks simple in CAD can force the tool to recut its own chips, which raises cutting temperature and leaves a poor floor finish. This is why a 4:1 depth-to-diameter pocket usually costs less than a 10:1 one, even when the removed volume is identical.

So the first engineering question is not which machine. It is how the tool reaches the feature, how the chips leave, and how the part is held while that happens. Everything downstream follows from those three answers.

Each new orientation of the part means a new fixture, a new zero point, and a new chance to stack error. Going from three setups to one can cut cycle time by 40% or more on a complex bracket, mostly in handling rather than in metal cutting. This is the real argument for multi-axis work, and it is a cost argument first.

On a 3-axis machine, the tool axis stays vertical. Undercuts, side holes and angled faces need the operator to stop, unclamp, rotate and re-probe. On a simultaneous 5-axis center, the A and B rotary axes tilt the tool so it approaches the feature from a direction that keeps a short, stiff tool. Short tools chatter less and hold tighter dimensions.

Positioning tolerance matters here. A Ø400 mm rotary table with a swing of a few microns at the center becomes tens of microns at the rim. If you are machining a hole pattern 300 mm from the table center, that amplification is already in your error budget before the tool touches metal.

The practical rule: group features by approach direction in your own design review. If a part has features on five faces, ask early whether they can be machined in one setup instead of five. That question is worth more than a tolerance negotiation.

GreatLight works to ±0.005 mm (±0.0002 in) on qualified features. That is not a default that applies to every dimension on a drawing. It applies where the process, the material and the inspection method can all support it, and it needs to be agreed feature by feature rather than stamped across the title block.

Surface finish follows a similar logic. As-machined surfaces land around Ra 1.6–3.2 μm, a good general machining target sits at Ra 0.8–1.6 μm, and fine work with sharp tooling and light finishing passes reaches Ra 0.2–0.8 μm. Below that range you are usually talking about lapping or polishing, which is a different operation and a different price.

Material behavior sets the ceiling. Aluminum 6061 and 7075 hold fine finishes readily. Stainless 316 and 17-4PH work-harden, so a finishing pass that rubs instead of cuts will tear the surface. Plastics like POM and PEEK move with temperature, so a dimension measured hot may not repeat when the part cools.

Inspection closes the loop. We check raw material on arrival, monitor dimensions in process, and inspect 100% before shipment, with reports available on request. If a feature cannot be measured reliably, its tolerance is a claim rather than a control.

A prototype run and a 10,000-part run are not the same job with a bigger quantity attached. The prototype usually machines from billet with generous stock and simple soft jaws. Production work justifies custom fixtures, optimized toolpaths and sometimes a casting or forging blank that removes 60% of the roughing time.

The bridge between them is the DFM review. We return a quotation and a free DFM analysis within 12 hours, flagging thin walls, deep pockets, unreachable radii and datums that cannot be fixtured. Production can start within 24 hours once the design is settled.

There is no minimum order quantity here. One prototype and a 10,000+ part run go through the same engineering review. That matters because the mistakes that hurt at volume are visible at quantity one, if anyone looks for them.

Parts typically ship in 3–5 days for standard work. Historical late-delivery probability sits below 2%, which is a record, not a promise. Build your schedule around the process, not around a date printed on a quote.

The material list is wide, but each family carries its own rules. Aluminum grades 6061, 2024, 5052, 6082 and 7075 cut freely and suit structural brackets, housings and heat sinks. ADC12 is a die-casting alloy, so it belongs to a different production route than billet machining.

Stainless 303 machines cleanly, 304 and 316 resist corrosion but gum up tools, and 17-4PH reaches high strength after heat treatment, which means final dimensions may need to be cut after that treatment. Steel grades 1018, 1045, 4130, 4140 and 4340 cover the range from mild fixtures to highly loaded shafts.

Titanium TA1, TA2 and TC4 (Ti-6Al-4V), plus Inconel and magnesium AZ31B or AZ91D, sit at the difficult end. They need rigid setups, sharp tooling and conservative parameters. Magnesium adds a chip-handling safety requirement that not every shop is equipped for.

Plastics behave differently again. ABS, PC, PMMA, POM, PA, PEEK, PP, HDPE and carbon fibre all machine, but they deflect, melt and absorb moisture at different rates. A 0.1 mm wall in PEEK is a very different risk than the same wall in 6061.