CNC Machining Dandenong: How the Process Works and Where It Fits

• 1
  What CNC Machining Dandenong Shops Actually Do to Metal
• 2
  Tolerance, Finish and the Cost Curve Behind Them
• 3
  Material Choice Changes the Cutting Data, Not Just the Price
• 4
  Where the Process Reaches Its Limit
• 5
  Inspection Is What Turns a Cut Part Into a Shippable Part
• 6
  Which Machining Route Fits the Part

CNC machining removes metal with a rotating cutting tool that follows a programmed path. The machine does not know what the part is. It only knows coordinates, feed rate and spindle speed. That is why the same process cuts an aluminium bracket or a titanium bone plate without changing the machine, only the tool, the coolant and the cutting data.

A three-axis mill moves the table in X, Y and Z. The tool always approaches from one direction, so any feature on the side or underside needs a second setup. Each extra setup adds a fixture, a re-clamp and a small position error. For parts with features on four or five faces, that stacking error is often the real limit, not the machine resolution.

Five-axis machining tilts the tool or the table so the cutter reaches angled faces in one setup. The benefit is not speed. It is that the datum stays the same from the first cut to the last, so hole-to-hole position holds tighter. On a part with 30 holes across three faces, that difference shows up in the inspection report.

Turning is different. The work rotates and a single-point tool feeds along the axis. Shafts, bushings and threaded fittings are turned, not milled. Mill-turn centers do both on one platform, which matters when a part has a turned body and milled flats that must stay concentric.

• 1
  3-axisFlat plates, pockets, one-face features. Lowest cost per part.
• 2
  4-axisAdds rotation around one axis. Good for cylindrical parts with slots.
• 3
  5-axisAngled faces and undercuts in one setup. Tighter position between faces.
• 4
  Mill-turnTurned body plus milled features without a second fixture.

Tolerance is the allowed band around a nominal dimension. A general tolerance of ±0.1 mm costs nothing extra on most parts. Push to ±0.005 mm and the shop has to control thermal growth, tool wear and fixture stiffness. The price does not rise in a straight line. It steps up.

Ask for tight tolerance only where the function needs it. A mounting hole that locates a bearing needs a tight bore. A clearance hole for an M6 bolt does not. If every dimension on the drawing carries the same tight band, the quote reflects the hardest one, not the average.

Surface finish is measured as Ra, the average roughness of the profile. As-machined finish sits around Ra 1.6–3.2 μm and is fine for brackets and housings. Sealing faces, sliding surfaces and bearing bores usually want Ra 0.8–1.6 μm. Optical and vacuum parts can need Ra 0.2–0.8 μm, which means slower feeds and sometimes a finishing pass with a smaller tool.

The two limits interact. A tight bore with a rough finish will not seal. A smooth surface on a loose dimension is wasted money. Write both on the drawing where they matter, and leave the rest at the general block tolerance.

• 1
  General±0.1 mm, no special control. Default for non-critical features.
• 2
  Close±0.02 mm. Needs sharp tools and stable fixturing.
• 3
  Fine±0.005 mm. Temperature and tool wear become variables.

Aluminium 6061-T6 is the default for machined prototypes and small runs. It cuts fast, holds a good finish and anodizes cleanly. 7075 is stronger but gummier and costs more. 2024 machines well but has poor corrosion resistance unless it is coated.

Stainless 304 and 316 work-harden. If the tool rubs instead of cutting, the surface gets harder and the next pass cuts worse. That is why stainless needs a positive feed, sharp inserts and no dwell. 17-4PH in the H900 condition is used for shafts and valve parts where strength and corrosion resistance both matter.

Titanium Ti-6Al-4V (TC4) has low thermal conductivity, so heat stays at the cutting edge. Tool life drops fast if coolant is poor. Inconel is harder still. Both are machinable, but expect slower cycle times and higher tool cost per part.

Plastics behave differently again. POM and PEEK hold dimensions well; ABS and PP flex under clamping and need soft jaws. Carbon fibre is abrasive and wears cutters quickly, so the tool path and the dust extraction matter as much as the spindle.

• 1
  Easy6061, 6082, brass C36000, POM. Fast cycles, good finish.
• 2
  Moderate304, 316L, 4140, 7075. Watch work hardening and heat.
• 3
  HardTi-6Al-4V, Inconel, 440C. Slow speeds, short tool life.

CNC machining is subtractive. The tool has to reach the feature, and it has to get out again. A deep pocket narrower than the cutter length-to-diameter ratio allows will chatter or break the tool. A rule of thumb: keep pocket depth under four times the cutter diameter where you can.

Internal corners are cut by a round tool, so they always carry a radius. If the drawing calls for a sharp internal corner, someone has to broach it or EDM it. Design the radius in, usually at least one third of the pocket depth, and the part gets cheaper.

Thin walls move. A 0.5 mm wall on a 100 mm aluminium part will deflect under clamping and spring back after the cut. For walls under 1 mm, expect to add a finishing pass at low depth of cut and possibly a support fixture.

Threads, small holes and fine text have their own floors. Holes under Ø1 mm need a spot drill and a peck cycle. Laser marking holds a minimum character height of about 1.5 mm. Below that, the mark gets unreadable and the process is the wrong one.

When a feature cannot be machined, the answer is often to split the part or change the process. Die casting, sheet metal or 3D printing each cover ground that a mill cannot.

• 1
  Deep pocketsKeep depth under 4× cutter diameter or add a rougher.
• 2
  Internal cornersAlways radiused by the tool. No sharp square corner.
• 3
  Thin wallsUnder 1 mm needs light finishing passes and support.

A machine repeats a path. It does not know whether the part is right. Inspection closes that gap. The first article is measured against the drawing, then in-process checks catch drift as tools wear.

CMM and optical comparators are the usual tools for critical dimensions and profile. For a first article, a full dimensional report shows every callout on the drawing. For production, a shorter report on the key characteristics is usually enough.

Material traceability matters in regulated work. Aerospace, automotive and medical programs want to know the heat number of the bar stock, not just the alloy name. Keep the mill certificate with the job.

Final inspection before shipment is the last gate. A 100% check on critical features plus a sample check on the rest is normal practice. Reports go out on request, and the shop should be able to show the raw material record, the in-process log and the final data.

• 1
  First articleFull dimensional report against the drawing.
• 2
  In-processCheck critical features as tools wear.
• 3
  Final100% on critical, sample on the rest, before packing.