Amazing CNC Machine Project Guide

A three-axis machine moves the tool in X, Y, and Z. Every face you cannot reach from the top needs a second setup, a second fixture, and a second chance to lose datum alignment. A five-axis center adds two rotary axes, so the tool can approach a part from an angle. In practice this means a housing with ports on five sides can be cut in one setup instead of four.

One setup means one datum. That is the real gain. On a multi-setup job, each refixturing can shift the part by 0.01 mm or more depending on fixture stiffness and how hard the operator clamps it. On a five-axis job with a Ø400 mm rotary table, the part is located once and the table does the moving. Tolerance stacks get shorter.

Five axes are not always faster. For a simple plate with holes on one face, a three-axis mill with a good fixture will beat a five-axis job on cycle time and cost. Reach for simultaneous five-axis when the geometry has compound angles, deep pockets with undercut walls, or features on non-orthogonal faces. Otherwise the extra setup is cheaper than the extra machine time.

Our shop runs 16 simultaneous five-axis machining centers, 12 four-axis mills, 27 three-axis machines, and 16 mill-turn centers. That mix matters at quoting: we pick the machine that fits the geometry instead of forcing everything onto one platform. Maximum processing size is 4,000 mm, with travels from 4,000 × 400 × 150 mm down to 500 × 310 × 200 mm for compact parts.

• 1
  Use five axes whenCompound angles, undercuts, five-sided features, tight position between faces.
• 2
  Use three axes whenFlat plates, single-face drilling, simple profiles, high volume on one face.
• 3
  Watch fixture stiffnessThin walls deflect under clamping load even with a perfect program.

±0.005 mm is achievable on our equipment, but it should be applied to the features that need it, not printed across the whole drawing. A general block tolerance of ±0.1 mm with two or three tight callouts is cheaper and easier to inspect. When every dimension is tight, the machinist slows down, inspection time grows, and the quote reflects both.

Surface finish follows the same logic. Ra 0.8–1.6 μm is a normal machined finish for most functional surfaces. Ra 0.2–0.8 μm usually means a finishing pass with a smaller stepover or a separate operation, and it raises cost. As-machined surfaces at Ra 1.6–3.2 μm are fine for brackets, covers, and internal faces that never touch another part.

Two design details bite harder than tolerance. First, deep pockets with small corner radii: a Ø3 mm cutter needs to reach the corner, and a 40 mm deep pocket at that diameter will chatter without a reduced stepdown. Second, sharp internal corners on a milled part cannot exist, because every cutter has a radius. Call out the largest acceptable corner radius and the shop can use a stiffer tool.

Add a datum scheme to the drawing. If the inspector and the machinist pick different datums, a conforming part can read as out of tolerance. On machined parts we mark datums on the first article and note the setup orientation. We inspect 100% of parts before shipment, with raw material checks, in-process monitoring, and a final report available on request.

Aluminium 6061-T6 is the default for prototypes and functional parts because it machines fast and holds tolerance well. 7075 gives higher strength for aerospace brackets but cuts slower and costs more. If a part will be anodized, note that 6061 and 7075 take clear and colored anodizing differently, and hardcoat changes the surface by roughly half the coating thickness per side.

Stainless 303 turns and mills more freely than 304 or 316, which is why it shows up on shafts and fittings. For medical or food-contact parts, 316L is the usual pick, but it work-hardens and needs a rigid setup. 17-4PH (SUS630) can be heat treated after machining for higher strength, so leave stock if a post-machining heat treat is planned.

Titanium TC4 (Ti-6Al-4V) and Inconel are where projects get expensive. Both hold heat at the cutting edge, so tool life drops and cycle time rises. Design them with generous radii and avoid thin unsupported walls. For housings that do not need high strength, magnesium AZ31B and AZ91D cut fast and are lighter, but they need chip handling controls.

Plastics are their own case. POM and ABS machine cleanly; PEEK and carbon fibre are abrasive and will wear tooling. Plastics also move after machining as internal stress releases, so specify a stress-relief step or accept a looser tolerance on large flat parts.

• 1
  Aluminium 6061-T6Prototypes, fixtures, enclosures. Fast, stable, anodizes well.
• 2
  Stainless 316LMedical and marine. Expect slower speeds and rigid workholding.
• 3
  Ti-6Al-4VAerospace brackets. Plan for short tool life and higher cost.
• 4
  PEEK, carbon fibreAbrasive. Tool wear and edge quality need attention.

The first article and the production part should be made the same way. If the prototype comes off a five-axis center but production moves to a three-axis fixture, the tolerance stack changes and the first production parts may not match. Decide early whether the design is a one-off or a program part.

For low volume, no minimum order quantity applies. We run from a single prototype to 10,000+ part runs. At the prototype stage, a DFM review within 12 hours will flag features that will not machine as drawn, such as a corner radius smaller than the tool that has to reach it. Production can start within 24 hours after approval, and parts ship in 3–5 days.

Inspection planning belongs in the same conversation. A cosmetic part needs a finish check and a visual standard; a hydraulic manifold needs dimensional reports and possibly pressure testing. Tell us which dimensions are functional. That short list drives the inspection plan far more than a general note to inspect all features.

If the part needs finishing after machining, plan the sequence. Anodizing, electroless nickel, zinc plating, powder coating, and black oxide all add or change dimensions slightly. Bead blasting, tumbling, brushing, and polishing change surface texture. Laser marking needs a minimum character height of 1.5 mm to stay legible after coating.

Machining is subtractive. Every part starts as a block or bar and the rest becomes chips. That is fine for a bracket, but expensive for a part where 80% of the material is removed. If a design has a large hollow body with thin walls, die casting or vacuum casting may be the better route at volume.

Very thin walls are another limit. A 0.5 mm aluminum wall over a 100 mm span will deflect during clamping and again after the vise releases. Sometimes the fix is a redesign with a rib, not a slower program.

Finally, do not machine a part that needs internal channels no tool can reach. Conformal cooling channels inside a mold insert, for example, are a job for metal 3D printing. Our services include custom 3D printing and metal die casting, so the right answer may sit outside the CNC department.

If your project is a genuine fit for milling or turning, the shop details are simple: three wholly-owned plants, 7,600 m² of floor space, 150 technicians, and 127 high-precision CNC machines. The part still has to make sense on a machine.