CNC Microprocessing

• 1
  What CNC microprocessing actually does
• 2
  Where the practical limits sit
• 3
  CNC microprocessing against other micro methods
• 4
  How micro parts get verified
• 5
  Design rules that keep micro parts machinable
• 6
  Choosing a micro process by feature type

CNC microprocessing is subtractive machining where the cutting tool is small enough that the chip load, the tool tip radius, and the material grain size all sit in the same range. A Ø0.5 mm end mill does not behave like a Ø6 mm end mill. It deflects more, it heats up faster, and it wears on a different curve.

That is the whole difficulty. The machine moves the same way. The physics do not scale down with the drawing. When you shrink a feature to 0.2 mm, the tool that cuts it may be 0.15 mm in diameter, and suddenly the stiffness of that tool, not the stiffness of the machine, sets your limit.

So CNC microprocessing is less about buying a micro machine and more about controlling the small-tool problem. Feed per tooth, spindle speed, coolant delivery, and tool runout all matter more here than on a 50 mm face mill. Get them wrong and the tool snaps inside a cavity you cannot reach.

We run this work on 127 high-precision CNC machines, including 16 simultaneous 5-axis machining centers and 16 mill-turn centers. The machines help. The process control is what decides whether the part comes out at ±0.005 mm or scrap.

• 1
  Small tools bendA Ø0.5 mm end mill deflects 20–50× more than a Ø6 mm tool at the same load.
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  Grain size mattersIn fine-grained metals, the cutting edge can be smaller than the grain boundary spacing.
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  Heat has nowhere to goLow mass and low feed mean the chip carries off less heat than in macro cutting.

Micro milling holds ±0.005 mm (that is ±0.0002 in) on features where the tool can reach without excessive length-to-diameter ratio. Keep the tool below 5× diameter in overhang and the tolerance is repeatable. Push past 10× and you are gambling on runout and chatter.

Surface finish follows the same logic. A stable micro cut on 6061-T6 or 316L typically lands at Ra 0.8–1.6 μm. With a light finishing pass and a sharp tool, Ra 0.2–0.8 μm is achievable on a good day. As-machined faces without a finishing pass sit around Ra 1.6–3.2 μm.

Feature size is the harder limit. Slots narrower than 0.3 mm, walls thinner than 0.2 mm, and internal radii under 0.1 mm start to fight the tool geometry itself. At that point you are choosing between a very fragile cutter and a different process entirely.

Material choice shifts the window. Aluminum and brass micro machine cleanly. Titanium (Ti-6Al-4V) and Inconel cut hot, wear tools fast, and need lower surface speed and more coolant pressure. Plastics like PEEK or POM machine easily but can burr and melt if the feed is too light.

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  Tool overhangKeep below 5× diameter for predictable tolerance; 10× is the practical ceiling.
• 2
  Wall thicknessBelow 0.2 mm, deflection and vibration start to dominate the result.
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  Internal radiusUnder 0.1 mm, the cutter geometry, not the CNC, sets the limit.
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  Material effectAluminum and brass are forgiving; titanium and Inconel demand slower feeds and more cooling.

Micro milling and micro turning are not the only ways to make a small metal part. EDM, laser cutting, photochemical etching, and micro injection molding all compete for the same jobs. The question is which one fits the geometry, the material, and the quantity.

EDM wins when the feature is a sharp internal corner or a hardened material that a cutter cannot touch. It is slower per part and needs a electrode, but it holds tight detail. For a 0.05 mm slot in hardened tool steel, EDM is the honest answer.

Micro milling wins on 3D geometry, mixed features, and one-off or low-volume parts. It cuts multiple features in one setup, leaves a machined surface, and does not need a custom electrode. For a 20 mm aluminum housing with small bores and a pocket, milling is faster and cheaper.

Laser cutting and etching win on flat, thin parts in high quantity. They cannot hold a 3D profile or a tight bore diameter. Micro molding wins when you need thousands of identical plastic parts with fine detail and can absorb the tooling cost. Below that volume, machining is usually the better economic call.

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  Sharp internal cornerEDM, because a rotating cutter always leaves a radius.
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  3D contour, low volumeMicro milling, because one setup cuts all the features.
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  Flat thin part, high volumeLaser or etching, because setup cost per part is tiny.

A ±0.005 mm part does not get verified with calipers. Micro features need optical measurement, video measurement, or a CMM with a small stylus. The probe tip itself has a radius, and on a 0.3 mm slot that radius is a real part of the measurement uncertainty.

We inspect 100% of parts before shipment. That means raw material check, in-process monitoring, and final inspection. Reports are available on request. For micro work, in-process monitoring matters more than final inspection, because by the time the part is finished, a drifting tool has already cut twenty bad features.

Temperature control is part of the measurement, not a separate concern. A 0.5 mm aluminum feature grows and shrinks with the room. Measuring in a warm shop and comparing to a 20 °C drawing will show errors that are not really there.

If your drawing calls out a tolerance tighter than ±0.005 mm on a tiny feature, talk to us before you release it. Sometimes the number is real and needs a different process. Sometimes it is a habit carried over from a larger part, and relaxing it saves cost without affecting function.

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  Optical and video measurementBest for small slots, edges, and features a probe cannot reach.
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  CMM with small stylusReliable for bores and position, but stylus radius affects tiny features.
• 3
  Temperature stabilityMeasure near 20 °C or accept the thermal error in your numbers.

Most micro parts that fail in production were designed without a tool in mind. A 0.1 mm internal radius in a 5 mm deep pocket is not a tolerance problem, it is a geometry problem. The cutter that fits the radius cannot reach the depth. We flag this in DFM before cutting.

Add a small relief at the bottom of blind pockets and internal corners when the function allows it. A 0.2 mm corner relief lets a standard micro end mill clear the feature without a special tool. It costs nothing at the design stage and removes a whole class of production problems.

Avoid thin unsupported walls where possible. A 0.15 mm wall on a 10 mm tall feature will vibrate during cutting and may distort after. If the wall is structural, consider a small rib or a change in material rather than a tighter tolerance.

Keep datum features large enough to hold. On a 5 mm part, a 0.5 mm datum face is not a reliable reference. A slightly larger datum pad, even 1 mm, gives the setup something to clamp and measure against, and it improves the whole part.

• 1
  Add corner reliefA 0.2 mm relief lets a standard micro tool clear an internal corner.
• 2
  Open up pocket bottomsA small radius at the floor reduces tool load and improves finish.
• 3
  Support thin wallsAdd a rib or increase thickness instead of tightening tolerance.
• 4
  Keep datums usableA 1 mm datum face is far more reliable than a 0.5 mm one.