CNC Micro Machining Parts Service: 7 Checks Before You Order

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  Key takeaways
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  Which micro machining route fits your part
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  What a CNC micro machining parts service actually covers
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  Tolerance and datum strategy: where ±0.005 mm holds
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  Material behavior on micro features
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  Supplier checks: certification, inspection and quoting
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  Quantity, setup cost and where the money goes
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  Step by step: qualifying a micro machining supplier

Micro machining is not simply machining small parts. A 10 mm bracket with a 0.5 mm cross hole is small work. A 60 mm manifold with a 0.4 mm orifice and a flatness callout of 0.005 mm is micro work. The difference sits in the feature, not the envelope. When engineers ask us for a CNC micro machining parts service, we look at the smallest dimension on the drawing first, then at the material, then at the quantity.

The practical floor for milling is a tool diameter around 0.2 mm. Below that, the tool snaps before the cut finishes, and runout eats most of your tolerance. Holes are a separate case. Micro drilling reaches Ø0.3 mm in aluminium, but stainless and titanium push the limit up toward Ø0.5 mm because the drill walks. For anything under those numbers, EDM or laser becomes the honest answer.

Surface finish follows the same logic. Ra 1.6–3.2 μm is normal as-machined output. Ra 0.8–1.6 μm is a controlled finishing pass. Ra 0.2–0.8 μm on a micro feature usually needs a light finishing pass with a fresh tool, plus careful handling afterward. A shop that promises Ra 0.2 μm on a 0.3 mm pocket without naming the process is guessing.

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  Feature firstSmallest hole, slot or wall drives the process choice.
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  Material secondStainless, titanium and ceramics shift the limits.
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  Quantity thirdOne prototype and 10,000 parts use different setups.

A ±0.005 mm tolerance is achievable on our machines, but not on every feature of every part. It holds well on a bored hole in aluminium when the hole is at least 3× the tool diameter and the wall is stiff. It gets difficult on a long thin rib, a deep narrow slot, or a feature far from the datum. Thermal growth matters too: a 100 mm aluminium part moves about 0.002 mm per 1 °C change.

Datum choice decides whether the tolerance is even measurable. If the drawing calls a 0.005 mm position on a hole but the datum is a rough cast surface, no shop can hold it. Put the datum on a machined face, and keep the tight features close to it. Where a tight callout is unavoidable far from the datum, ask for an in-process probe check rather than a final one.

Watch the difference between tolerance and process capability. A shop may hold ±0.005 mm on one part and miss it on the next fifty because tool wear was not compensated. Ask how the process is monitored: tool life counts, in-process probing, or a first-article plus periodic check. That answer tells you more than the tolerance line on a website.

Micro parts also suffer from clamping. A 0.2 mm wall can deform under a vise jaw and spring back after unclamping, so the measured part differs from the machined one. Good shops use custom soft jaws, vacuum fixturing or low-melt holding for thin walls. If your drawing has walls under 0.5 mm, mention it in the RFQ so the shop can plan the fixture.

Aluminium 6061 and 7075 are the easiest starting point for micro work. They cut fast, hold a sharp edge and tolerate small tools. 7075 gives better stiffness for thin walls, but it is more prone to chipping at the exit of a micro hole. 2024 sits in between. For housings and brackets with fine features, 6061-T6 is usually the lowest-risk choice.

Stainless 303 machines cleanly but is not ideal for medical or food contact. 304 and 316L are common in medical devices; 316L work-hardens quickly, so micro tools need constant feed and no dwelling. 17-4PH holds strength after heat treatment and is used for instrument parts. Expect slower cycle times and shorter tool life than aluminium.

Titanium Ti-6Al-4V and Inconel are the hard cases. Both generate heat at the cutting edge, and a 0.3 mm tool has almost no material to carry that heat away. Cutting speeds drop, coolant becomes mandatory, and thin walls distort. If your design allows aluminium for the prototype and titanium for production, do that. It shortens the learning loop.

Plastics and ceramics need their own notes. POM and PEEK machine well but burr at micro edges; a light chamfer prevents handling damage. PMMA cracks if the tool rubs instead of cuts. Technical ceramics such as alumina and zirconia are usually shaped by diamond grinding, with CNC used for fixtures and secondary features. Do not assume a standard carbide end mill will touch them.

Certification is a filter, not a score. ISO 9001:2015 covers general quality systems. IATF 16949:2016 matters for automotive and EV programs. ISO 13485:2016 matters for medical devices. ISO 27001:2022 covers information security, which is relevant if you upload CAD files for micro parts under NDA. Match the certificate to your industry, not to a longer list.

Inspection capability is where micro work is won or lost. A shop that only has calipers cannot verify a 0.3 mm hole. Ask which instrument measures your smallest feature: optical comparator, vision system, non-contact 3D scanning, or a coordinate measuring machine with a small stylus. Then ask whether the report ships with the parts or only on request. For micro features, we recommend a report by default.

Quoting behavior tells you a lot. A useful quote names the process, the number of setups, the estimated cycle time and the inspection method. A quote that lists only a price and a lead time is a warning sign. We return a quotation and a free DFM analysis within 12 hours, and production can start within 24 hours after approval.

Finally, check the confidentiality path. Uploads should be secure and confidential, and an NDA should be available on request. If your part is a medical or defense design, confirm who inside the shop can open the file and where the data lives. That is a process question, not a legal formality.

On micro parts, setup and inspection usually cost more than cutting time. A three-setup part with a 0.3 mm feature might run 4 minutes of spindle time and 30 minutes of fixturing and probing. That is why the price curve flattens slowly at low quantities. If your program is at 50 pieces, ask whether two setups can be combined rather than asking for a discount.

There is no minimum order quantity here, from one prototype to 10,000+ part runs. But the unit price at one piece is not a predictor of the unit price at 10,000. Micro tool life, in-process inspection and packaging dominate at volume. If you plan a ramp, send both quantities in the RFQ so the shop can propose a process that survives the ramp.

Tooling is the other lever. Standard micro end mills are cheap and fast to replace. Custom form tools cost more and add lead time, but they can remove a finishing operation. For a part with a repeated radius or groove, the custom tool often pays back at a few hundred pieces. Ask for both options in writing.

Packaging matters more than people expect. A tray of 0.3 mm pins can be destroyed by a bubble bag. Ask how finished micro parts ship, and whether individual compartments are used. If your assembly line needs parts in order, say so before the quote, not after.