CNC Machining: Start Your Journey

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  How CNC machining removes material
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  When 3-axis is enough and when you need 5-axis
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  What each material does to your process plan
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  How tolerance and finish are actually held
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  From drawing to shipped parts
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  Which setup fits your part

To cnc machining start your journey, the first thing to understand is that this is a subtractive process. A CAD model becomes toolpaths, the toolpaths become G-code, and a controller drives the spindle and axes along those coordinates. The cutter enters solid stock and removes material until the remaining shape matches the model. Nothing is molded or layered, so the mechanical properties of the billet carry through to the finished part.

The cutting edge does the real work. Each tooth takes a small chip, and the chip thickness depends on feed per tooth, spindle speed and radial engagement. Too light a chip and the edge rubs, work-hardens stainless and wears fast. Too heavy and you get chatter, poor finish and possible tool breakage. Feeds and speeds are matched to material, cutter geometry and rigidity.

Heat is the constraint that decides everything else. Most heat leaves with the chip, so coolant or air blast matters as much as the numbers. Aluminium 6061 and 7075 cut fast with high spindle speeds. Stainless 316 and 17-4PH run slower with constant cooling. Titanium TC4 and Inconel need lower surface speed and rigid setups because they hold heat at the edge.

The machine does not correct a bad setup. If the vise or fixture lets the part move 0.05 mm under load, the cutter follows the part, not the program. Rigidity, workholding and tool stick-out set the achievable tolerance long before the controller does.

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  Chip loadFeed per tooth decides edge life and finish quality.
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  Heat pathMost heat should leave with the chip, not the part.
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  RigidityWorkholding and tool stick-out set real tolerance.

A 3-axis mill moves X, Y and Z with the tool always pointing down. It is the fastest and cheapest way to make a part with open features: plates, brackets, housings with reachable pockets, and anything machined from a few faces. If every feature can be reached from six directions without re-fixturing tricks, 3-axis is the right call.

The limit appears when features sit on angled faces or wrap around a part. On a 3-axis machine you flip the workpiece, re-indicate it and cut again. Each setup adds alignment error and time. A part needing four setups can drift 0.02 mm between operations even with good fixtures, because the datum moves with each flip.

Five-axis machining tilts the tool or the table so the cutter reaches the feature in one setup. GreatLight runs 16 simultaneous 5-axis machining centers with a Ø400 mm rotary table, which suits impellers, turbine blades, orthopedic implants and complex automotive housings. One setup means one datum, and that is where the accuracy gain comes from.

Five-axis is not automatically better. It costs more per hour, and programming takes longer. For a simple bracket the extra cost buys nothing. Choose 5-axis when setup count, angle access or surface continuity drive the part, not because the machine sounds more capable.

Aluminium is the easiest place to begin. Grades 6061, 6061-T6, 7075 and 6082 cut cleanly at high speed and hold ±0.005 mm without drama. They suit prototypes, housings, heat sinks and brackets. Soft grades like 5052 gum up on tapping, so use form taps or larger minor diameters. Anodizing adds a hard surface but changes dimensions by a few micrometres per side.

Stainless 303 and 304 machine reasonably well with sharp tooling and steady feed. Grades 316 and 316L work-harden if the cutter dwells, so keep the chip load up and avoid spring passes. 17-4PH in the H900 condition is tough but predictable. For medical parts, 316L and titanium TC4 are common, and both reward rigid setups over fast feeds.

Titanium and Inconel sit at the hard end. TC4 conducts heat poorly, so the edge runs hot and tool life drops fast. Low surface speed, high pressure coolant and short tool overhang are the standard answers. Inconel is worse still, and we usually plan extra roughing passes and inspect between them. Magnesium AZ31B and AZ91D cut fast but need chip control for fire safety.

Plastics behave differently again. POM and PA hold tolerance well, ABS and PMMA are softer and prone to burrs, and PEEK needs sharp edges and low heat. Carbon fibre eats carbide, so diamond-coated tooling pays for itself on any real volume.

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  Start with aluminium6061-T6 gives the cleanest path to a first good part.
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  Watch work-hardening316L and 17-4PH punish light, dwelling cuts.
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  Plan for heatTC4 and Inconel need low speed and heavy cooling.

Tolerance is a budget, not a single number. A ±0.005 mm callout on one bore is achievable on a rigid machine with the right boring head. The same callout on every dimension of a thin-walled part is not, because the wall deflects under clamping and cutting force. Spend the tight tolerance where it functions and relax the rest.

Surface finish follows the same logic. As-machined surfaces land around Ra 1.6–3.2 μm. A careful finishing pass reaches Ra 0.8–1.6 μm. Fine finishes down to Ra 0.2–0.8 μm need dedicated finishing tooling, light radial engagement and often a separate operation. This is measurable, so say which surfaces need it rather than applying one note to the whole drawing.

Inspection backs the claim. GreatLight checks raw material on receipt, monitors dimensions in process and runs a final inspection on 100% of parts before shipment, with reports available on request. If a feature is hard to measure, a CMM report tells you what the machine actually produced instead of what the program intended.

Certification matters for regulated work. ISO 9001:2015 covers general quality systems, IATF 16949:2016 covers automotive, ISO 13485:2016 covers medical devices and ISO 27001:2022 covers information security. Ask which one applies to your part before you assume a supplier holds all four.

The journey starts with a 3D model and a 2D drawing carrying tolerances, material, finish and any critical features. A STEP file alone is not enough for a first order, because it says nothing about which dimensions matter. Send both, plus a note on how the part is used, and DFM feedback gets sharper.

Quotation and free DFM analysis come back within 12 hours. Production can start within 24 hours of approval, and parts typically ship in 3–5 days. There is no minimum order quantity, so a single prototype and a 10,000-part run both fit the same process. Uploads are handled under NDA on request.

During production the part moves through roughing, semi-finishing and finishing, then secondary operations such as anodizing, electroless nickel, powder coating, bead blasting or laser marking with a minimum character height of 1.5 mm. Each step can change size slightly, so finishing allowances belong in the model from day one.

The most common first-order mistake is a drawing that hides the real requirement. If a bore must mate with a bearing, say so. If a surface is only cosmetic, say that too. Clear intent removes guesswork and usually removes cost at the same time.