Aftons accurate CNC machining for accurate results

On a drawing, accuracy splits into a few separate things: dimensional tolerance, geometric tolerance, and surface finish. A part can hit ±0.005 mm on a caliper measurement and still fail because a bore is out of round or a face is not flat. When we review a print, we read all three together, because they interact.

Dimensional tolerance is the easiest to talk about. It sets a size band, such as a 20 mm bore allowed to land between 19.995 and 20.005 mm. Geometric tolerance is harder. It controls form, orientation, and position, so a shaft can be the right diameter and still not fit a bearing. Surface finish affects both: a rough wall changes the effective fit even when the size is correct.

Aftons accurate CNC machining starts with reading which of the three the part actually needs. Marking every dimension ±0.005 mm raises cost and lead time for no benefit. Marking only the critical fits keeps the price down and the inspection focused.

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  Size toleranceSets the allowed size band for a feature.
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  Geometric toleranceControls roundness, flatness, perpendicularity, and position.
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  Surface finishChanges fit and wear even when size is correct.
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  Callout strategyTighten only the fits that carry load or seal.

The axis count is a setup decision, not a badge of quality. A plate with holes on one face runs fastest on a 3-axis mill. Adding a fourth axis helps when the part has features on several sides and you want them cut without re-fixturing. Five-axis work pays off when the geometry is contoured, when you need to reach an undercut, or when a single setup removes stack-up error.

Re-fixturing is where accuracy usually leaks away. Every time a part moves to a new vise or a new fixture, a small offset enters the stack. On a part with a ±0.02 mm true position between two faces, three setups can eat most of the budget before the cutter touches metal.

Aftons runs 16 simultaneous 5-axis machining centers, 12 four-axis mills, 27 three-axis machines, and 16 mill-turn centers. That mix lets us pick the machine that matches the feature, rather than forcing every job onto the most expensive one.

Not every part belongs on five axes. Simple prismatic parts and short-run brackets are cheaper and faster on 3-axis. We say so when the print allows it.

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  3-axisFlat plates, single-face features, simple brackets.
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  4-axisFeatures on several sides, reduced re-fixturing.
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  5-axisContoured surfaces, undercuts, tight true position.
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  Mill-turnRound parts with milled flats or cross holes.

The same program cuts differently in aluminium and in stainless. Aluminium 6061 and 7075 cut clean and hold ±0.005 mm well when the wall is thick enough. Stainless 304 and 316 work-harden, so light passes and sharp tools matter more than spindle speed. Titanium TC4 (Ti-6Al-4V) moves under heat and needs coolant and conservative feeds.

Thin walls are the common failure case. A 0.8 mm aluminium wall will deflect under cutting force, spring back, and measure differently after the vise opens. We add support, take lighter passes, or rough and let the part rest before finishing.

Plastics behave differently again. POM and PEEK hold size better than ABS or PP, which flex and creep. Carbon fibre cuts well but wears tools fast and needs dust control.

We machine aluminium 6061, 6061-T6, 2024, 5052, 5083, 6063, 6082, 7075, and ADC12; stainless 303, 304, 316, 316L, 420, 430, 431, 440C, and 17-4PH; steels 1018, 1045, 4130, 4140, 4340, A36, and tool steel; copper and brass grades including C36000; titanium TA1, TA2, TC4, Inconel, and magnesium AZ31B and AZ91D; and plastics from ABS to PEEK.

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  AluminiumStable and fast. Best starting point for tight tolerance.
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  StainlessWork-hardens. Sharp tools and light passes required.
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  TitaniumHeat-sensitive. Coolant and reduced feeds needed.
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  PlasticsPOM and PEEK hold size. ABS and PP flex.

Surface finish is not decoration. A sealing face at Ra 0.8–1.6 μm holds a gasket better than an as-machined Ra 1.6–3.2 μm surface. Bearing bores often need Ra 0.2–0.8 μm. Coating adds thickness, so a hardcoat anodize layer changes a bore by a few micrometres and must be planned for before cutting.

We offer anodizing in clear, colour, hardcoat, and conductive grades; electroless nickel, zinc, silver, and gold plating; powder coating and black oxide; bead blasting, tumbling, brushing, and polishing; and laser marking with a minimum character height of 1.5 mm.

Inspection is where claims get tested. We check raw material before cutting, monitor in process, and inspect 100% before shipment. Reports are available on request. For a ±0.005 mm feature, that means a CMM or a suitable gauge, not a caliper.

Quality systems cover ISO 9001:2015, IATF 16949:2016, ISO 13485:2016, and ISO 27001:2022. The last one covers how your files are handled, which matters when the drawing is confidential.

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  Sealing facesTarget Ra 0.8–1.6 μm for gasket contact.
• 2
  Bearing boresTarget Ra 0.2–0.8 μm for fit and wear.
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  Coating allowancePlan thickness before the final cut.
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  VerificationCMM or gauge for tight features, not a caliper.