Buyer guide

Micro CNC machining service explained

This guide explains what a micro CNC machining service actually does, and how to judge whether a shop can hold ±0.005 mm on features under 1 mm. It is written for design engineers and sourcing engineers who need to pick a supplier, not a brochure. Read it before you send drawings out for quote.

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±0.005 mm toleranceØ0.2 mm toolingNo MOQ100% inspection

On this page

1
Key takeaways
2
What to compare before you award a micro machining job
3
What micro CNC machining service actually covers
4
Tolerance, finish and the physics behind the numbers
5
When micro CNC is the wrong process
6
Inspection, documentation and certification scope
7
Step by step: how to scope and release a micro machining job

Quick answer

Key takeaways

Micro means small tools, not small machinesBelow Ø1 mm cutter diameter, spindle speed, runout and chip evacuation decide the result, not the machine footprint.

Ask for runout numbers, not just toleranceA shop holding ±0.005 mm will quote spindle runout and tool holder data when you ask for it.

Tool diameter sets the smallest internal featureA Ø0.2 mm end mill cuts a corner radius no tighter than 0.1 mm, no matter what the drawing says.

Inspection cost scales with feature countMicro parts often need 100% inspection, so agree on the report format before production.

Prototype and volume should share one processSame machine class, same fixture logic, so the first article predicts the 10,000-part run.

Selection criteria

What to compare before you award a micro machining job

Use this table as a quote checklist. Each row is a question you can send to every shop on your shortlist.

Criterion	What good looks like	Red flag	How to verify
Tolerance on micro features	±0.005 mm stated for the specific feature	One blanket tolerance for the whole drawing	Ask for a capability sheet per feature type
Spindle speed and runout	High-speed spindle with low runout at the tool tip	No runout figure offered	Request a TIR measurement on the actual holder
Smallest tool on hand	Ø0.2 mm end mills stocked and reordered	Tooling ordered per job only	Ask which micro cutters are in the crib today
Inspection method	Optical or CMM with a written report	Visual check only on micro parts	Ask for a sample first-article report
Minimum order quantity	No MOQ, one piece to 10,000+	Setup fee that never amortizes	Confirm pricing at 1, 100 and 10,000 pieces
Certifications	ISO 9001, IATF 16949, ISO 13485, ISO 27001	Certificates shown but no scope	Check the scope covers your part class
Lead time	Quote and DFM within 12 hours	Vague 'depends on the shop load'	Ask for the production start window
Confidentiality	NDA available on request, secure uploads	Drawings sent over plain email	Confirm the NDA path before sharing files

Section 1

What micro CNC machining service actually covers

Micro CNC machining is milling, turning and drilling applied to parts where the functional features sit between roughly 0.05 mm and 2 mm. The workpiece itself may be 100 mm long. The point is not the part size, it is the feature size. A microfluidic channel 0.3 mm wide, a 0.5 mm diameter hole through 3 mm of 316L, a 0.1 mm corner radius on a neural probe tip: these are micro features on otherwise normal parts.

That distinction matters when you write the RFQ. If you describe the part by its envelope, a shop may quote it as routine work and then struggle at the first slot. If you list the micro features with their tolerances, the right shop will quote the tooling, the spindle and the inspection time separately.

A micro CNC machining service explained properly also includes the front end: DFM feedback on wall thickness, tool reach and deburring access. On a 0.4 mm wall, a chamfer that looks harmless on screen can collapse the wall in the cut. Good shops flag that before the quote, not after the first article.

1
Feature-driven, not size-drivenQuote the tolerance of the smallest feature, not the outer envelope.
2
Tooling is part of the quoteMicro cutters break often; replacement cost belongs in the unit price.
3
Deburring is a design decisionA 0.05 mm burr on a micro slot can block a fluid path.

Section 2

Tolerance, finish and the physics behind the numbers

±0.005 mm sounds like a shop-floor promise. In practice it is a stack-up: spindle thermal growth, tool deflection, fixture compliance, material springback and measurement uncertainty. On a Ø0.5 mm end mill sticking 5 mm out of the holder, deflection is the dominant term. Reduce the stick-out and the same machine holds tighter.

Surface finish follows the same logic. Ra 0.8–1.6 μm is a normal machined finish on aluminum and brass at moderate feed per tooth. Getting to Ra 0.2–0.8 μm on a micro feature usually means slower feed, a sharper cutter and sometimes a finishing pass with a new tool. Ask what feed per tooth the shop plans, and whether the finish is measured or assumed.

Material choice shifts the window. 6061-T6 and C360 brass cut cleanly at small diameters. 316L work-hardens, so a dwell or a too-light feed will rub instead of cut and the edge will fail. Ti-6Al-4V and Inconel need lower surface speed and more rigid setups. None of this is exotic, but it changes cycle time, and cycle time is what you are really buying.

1
Deflection dominates below Ø1 mmKeep tool stick-out under 5× diameter where the geometry allows.
2
Finish is a process choiceRa 0.2–0.8 μm needs a dedicated finishing pass, not a slower roughing pass.
3
Stainless needs a real chip loadToo light a feed on 316L rubs the edge and work-hardens the surface.

Section 3

When micro CNC is the wrong process

Micro CNC is a subtractive process. It removes material with a spinning cutter, so it cannot make a sealed internal channel with no opening, and it cannot make a feature smaller than the tool that reaches it. If your design has a 0.05 mm internal radius at the bottom of a 10 mm deep pocket, no end mill will produce it in one setup.

Deep, narrow features are the other limit. A hole with an aspect ratio beyond roughly 10:1 in a micro diameter needs peck drilling, a stub drill and sometimes EDM. If the shop quotes it as a simple drill cycle, the quote is optimistic.

There are also cases where the part is better molded, cast or printed. A micro part with no tight tolerance on the internal geometry and a production volume in the tens of thousands may be cheaper as a die-cast or molded part with a light machining pass on the critical faces. Micro CNC wins when the tolerance is tight, the volume is low to medium, or the geometry needs to be revised quickly.

1
No blind internal channelsSubtractive tools need a path in and out.
2
Corner radius is tool-limitedThe smallest internal radius equals the cutter radius.
3
Aspect ratio above 10:1Expect peck drilling, EDM or a design change.
4
High volume, loose toleranceCasting or molding plus a finish pass may cost less.

Section 4

Inspection, documentation and certification scope

On a micro part, inspection is a large share of the cost. A 30-feature part with ±0.01 mm tolerances cannot be checked with calipers. It needs an optical comparator, a vision system or a CMM with a small stylus, and the operator time is real. This is why 100% inspection before shipment is common on micro work, and why the report format should be agreed up front.

Certification matters differently depending on your industry. ISO 9001:2015 covers the quality system. IATF 16949:2016 applies to automotive production parts. ISO 13485:2016 applies to medical devices. ISO 27001:2022 covers information security, which matters when you are sharing proprietary geometry. A certificate only helps if its scope covers the process and part class you are buying.

Ask for the first-article report on the actual part, not a generic sample. On micro work, the report should list the measured value, the nominal, the tolerance band and the instrument used. If a dimension is out, you want to know before the run, not after 500 pieces.

1
Agree the report format earlyDimension list, nominal, actual, tolerance, instrument.
2
Match the certificate to the industryISO 13485 for medical, IATF 16949 for automotive.
3
First article on the real partA generic sample report tells you nothing about your geometry.

Workflow

Step by step: how to scope and release a micro machining job

Follow these steps in order. Skipping step 2 is the most common reason a micro job goes wrong.

1
1. Separate micro features from the rest of the drawingList every feature under 2 mm with its own tolerance, surface finish and inspection requirement. Everything else is normal work and should be quoted separately.
2
2. Check tool reach before you releaseFor each internal corner, confirm the radius is at least half the smallest available cutter. A Ø0.2 mm end mill gives a 0.1 mm minimum radius. If the drawing asks for less, change the design or expect EDM.
3
3. Set the datum scheme for micro featuresMicro features stack up fast. Use one datum for the critical group and keep the tolerance chain short. Datum features that are themselves micro-sized are hard to fixture, so pick something at least 3 mm across.
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4. Ask for DFM feedback with the quoteSend the 3D model, the 2D drawing and the intended function. A useful shop returns wall thickness warnings, deburring notes and a suggested tolerance for non-critical faces within 12 hours.
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5. Agree on the first-article and inspection planDecide which dimensions are measured, on what instrument, and what happens if one is out. For medical and aerospace work, plan for 100% inspection before shipment.
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6. Keep one process from prototype to productionRun the prototype on the same machine class and fixture logic as the production parts. If the prototype is made on a different setup, the first article does not predict the run.
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7. Lock the confidentiality pathUse secure upload and an NDA before sharing geometry. Confirm who inside the shop can see the files and how long they are retained.

FAQs

Questions engineers ask before awarding a micro job

How small a feature can micro CNC actually cut?

With Ø0.2 mm end mills, a shop can cut slots and pockets down to that width and internal radii down to 0.1 mm. Holes below Ø0.3 mm usually move to micro drilling or EDM.

The practical limit is not the cutter alone. Tool stick-out, spindle runout and chip evacuation set the real floor. A 0.1 mm slot in a deep pocket is much harder than the same slot on an open face.

Is ±0.005 mm realistic on a micro part?

Yes, on specific features with a short tolerance chain, a rigid setup and a controlled temperature. It is not realistic as a blanket tolerance across a whole drawing with dozens of micro features.

Ask the shop to state which features it can hold at ±0.005 mm and which ones it recommends opening to ±0.02 mm. That conversation saves money and avoids a rejected first article.

What is a reasonable minimum order quantity for micro machining?

For machined micro parts, one piece is a normal starting point. Setup cost dominates at low volume, so the unit price at one piece is not a useful indicator of the production price.

Get pricing at three volumes, for example 1, 100 and 10,000 pieces. If the curve does not flatten, the shop is probably re-tooling per batch, which adds risk to the run.

Which materials are difficult at micro scale?

316L, Ti-6Al-4V and Inconel are the common hard cases. They work-harden or hold heat at the cutting edge, and a micro cutter has very little material to conduct heat away.

Aluminum 6061, brass C360 and 17-4PH in the annealed state cut more predictably at small diameters. If the part must be 316L, expect slower feeds and more frequent tool changes.

How should I compare quotes from two micro machine shops?

Line up the quotes by feature, not by total price. Check whether tooling, inspection and finishing are included, and whether the quoted tolerance matches the drawing.

A lower quote often means fewer inspection points or a looser finishing pass. Ask what is excluded, and ask for the inspection plan in writing.

What information speeds up a micro machining quote?

Send the 3D model in STEP, the 2D drawing with micro feature tolerances called out, the material and temper, the surface finish, the quantity and the function of the critical features.

Note which dimensions are functional and which are reference. That single distinction lets the shop focus its process plan where it matters and quote the rest economically.