CNC machining Raleigh: how the process actually works

• 1
  What CNC machining actually does to metal
• 2
  Why five-axis centers change the design rules
• 3
  Tolerances, surface finish and what drives cost
• 4
  Material choice and how it behaves on the machine
• 5
  From upload to shipped part: the actual sequence
• 6
  Post-processing and why it is not an afterthought
• 7
  Which machining approach fits your part

CNC machining is subtractive. A rotating cutter removes material from a solid block until the remaining shape matches the CAD model. Nothing is molded or layered, so the part inherits the grain, hardness and fatigue behavior of the stock you started with. That is the main reason machined parts behave differently from cast or printed ones under load.

The cutting edge does two things at once: it shears the material and it pushes heat into the chip. Get the balance wrong and the heat stays in the part, which moves the dimensions after the cut. Feed and speed control that balance. Aluminum 6061 runs fast with high rake angles; 17-4PH stainless runs slow with heavy coolant. Same machine, different charts.

For engineers in Raleigh, this matters because a machined bracket, manifold or housing is usually a structural or sealing part. You cannot fix a bad cut with paint. Either the geometry is right when it leaves the vise, or the assembly leaks.

The whole discipline is about controlling where the cutter is in three, four or five axes while managing deflection, heat and chip evacuation. Everything else is bookkeeping.

A three-axis mill moves X, Y and Z. The part stays fixed, so any face you need to machine must point up. Undercuts and angled holes need a second setup, a second fixture and a second chance to introduce error. Every re-clamp adds stack-up.

A five-axis center adds two rotary axes. The tool approaches the part from an angle, so undercut features and contoured surfaces get cut in one setup. On a complex housing, that can replace four operations with one. Fewer setups means fewer datum shifts and tighter true position across features.

We run 16 simultaneous five-axis machining centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers. Maximum processing size is 4,000 mm, and the Ø400 mm rotary table handles round parts that would otherwise need a lathe and a mill.

Five-axis is not always the answer. A flat plate with drilled holes is faster and cheaper on a three-axis machine. The rotary axes only pay off when the geometry has compound angles, deep pockets reached from the side, or tight position tolerances across several faces.

We hold ±0.005 mm (±0.0002 in) when the drawing calls for it. That number is a capability floor, not a default. Tightening a tolerance on a non-critical face adds inspection time, slower feeds and sometimes a second operation. It rarely improves the part.

Surface finish works the same way. As-machined Ra 1.6–3.2 μm suits most brackets and housings. Ra 0.8–1.6 μm is typical for sealing faces and sliding fits. Ra 0.2–0.8 μm needs finer tooling and lighter passes, and it only makes sense where a seal, bearing or optical surface demands it.

Cost comes from three places: setups, material removal volume and inspection. A part with one datum and generous tolerances on non-functional faces will always beat a part with six datums and ±0.01 mm everywhere.

The practical rule: put the tight tolerance where the function lives. Leave the rest loose. Drawings that do this come back cheaper and faster.

Aluminum 6061-T6 is the default for prototypes and light structural parts. It cuts fast, holds tolerance well and anodizes cleanly. 7075 gives higher strength for aerospace brackets but machines slower and is less weldable. 2024 sits between them with better fatigue resistance.

Stainless 303 machines freely and suits shafts and fittings. 304 and 316 resist corrosion but work-harden, so light passes and constant feed matter. 17-4PH (SUS630) holds high strength after heat treatment and is common in medical and aerospace parts. It is not a fast cut.

Titanium TC4 (Ti-6Al-4V) and Inconel are in a different class. Low thermal conductivity sends heat into the tool, so speeds drop and tool life becomes the constraint. These alloys are chosen for temperature and strength, not for ease of machining.

Plastics behave opposite to metals. POM and PEEK cut cleanly, but ABS and PC can melt or chip if the feed is wrong. Carbon fiber eats tooling. We machine all of these regularly, and the choice usually follows the service environment, not the shop floor.

It starts with a CAD file and a drawing. We return a quotation and a free DFM analysis within 12 hours. The DFM flags thin walls, deep pockets, unreachable features and tolerances that will cost more than they are worth. Fixing those before cutting saves weeks later.

Once the design is agreed, production can start within 24 hours. Raw material is checked on arrival, then the first article is inspected against the drawing. In-process monitoring runs through the batch, and every part gets a final inspection before shipment. Reports are available on request.

Parts ship in 3–5 days for most work. That timeline assumes the drawing is stable and the material is in stock. Exotic alloys and multi-operation parts take longer, and we say so at quote time rather than after.

We hold ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. The last one matters if your drawings are sensitive. Uploads are confidential and an NDA is available on request.

A machined surface is rarely the final surface. Anodizing adds corrosion resistance and color. Hardcoat anodizing adds wear resistance for sliding parts. Electroless nickel and zinc plating handle conductivity and corrosion on steel and copper alloys.

Bead blasting and tumbling remove tool marks and deburr edges. Polishing brings sealing faces to a mirror finish. Laser marking puts part numbers and traceability codes on the part, with a minimum character height of 1.5 mm so the mark stays readable after coating.

Doing these steps in-house keeps the part on one schedule and one inspection chain. When finishing is outsourced, the part leaves the quality system and comes back with a new set of variables.

The engineering point is simple: decide the finish before you finalize the drawing. A hardcoat anodize adds thickness. A tight bore that was correct before coating may not be correct after it.