Service for CNC Micro Machining Parts: How to Choose One

• 1
  What decides a micro machining quote
• 2
  How to compare three types of micro machining supplier
• 3
  What a service for CNC micro machining parts actually has to control
• 4
  Reading a quote for micro machining: what to look for
• 5
  When micro CNC is the wrong choice
• 6
  Materials and finishes at micro scale
• 7
  Lead time, MOQ and confidentiality in practice
• 8
  Five mistakes buyers make with micro machining
• 9
  Step by step: vetting a micro machining supplier

A micro part is not just a small part. Below roughly 2 mm in feature size, the forces on the tool stop behaving the way they do on a 50 mm bracket. A 0.5 mm end mill has very little stiffness, so it bends before it cuts. Cutting forces scale down faster than the tool does, which means the same feed per tooth that works on a large part will chatter or snap the tool on a micro feature.

Thermal behavior matters more, not less. A 20 mm aluminum part grows about 0.5 μm per degree Celsius. If the shop holds ±0.005 mm, a 2 °C swing in the room eats 20% of the tolerance before the tool touches the part. That is why micro work is often run in temperature-controlled rooms with coolant at a stable set point.

Chip evacuation becomes the hard problem. A 0.3 mm slot fills with chips in a few passes. If the chips are not cleared, the tool rubs instead of cutting, heat builds up and the edge dulls within minutes. High-pressure coolant or air blast is not a luxury at this scale.

The practical result: a service for CNC micro machining parts is judged by how it manages stiffness, heat and chips together. Machine spindle speed alone tells you very little.

• 1
  Feature size below 2 mmWhere tool deflection and chip clearance start to dominate the process.
• 2
  Wall thickness 0.3–0.5 mmMachinable with light passes and good support. Below 0.3 mm, expect distortion.
• 3
  Aspect ratio above 5:1Deep micro slots and holes need peck cycles and long-reach tooling.

A real quote for micro work lists the process route, not just a price. If the quote says "CNC machining" with no mention of the machine class, the fixture or the inspection method, you cannot tell whether the shop has quoted a 3-axis mill or a micro-capable 5-axis center. Both can produce the part. Only one will hold the tolerance on a repeat basis.

The second thing to read is the datum scheme. On a part 5 mm across, a 0.1 mm datum shift is 2% of the part width. If the drawing calls a datum off a thin rib, ask how the shop is going to hold that rib while it machines the rest. A good shop will often suggest a small tab or a sacrificial boss, then cut it off in a second op.

Third, check the material callout against stock availability. A 3 mm 316L bar is a standard item. A 3 mm Inconel 718 bar may have a longer lead time than the machining itself. Micro parts often use less material than the minimum order size of the stock, so the material lead time can dominate the schedule.

Finally, look at how the quote handles one-off versus repeat. A shop that runs one prototype on a 5-axis center and then moves the part to a dedicated fixture for 10,000 pieces is planning for you. A shop that plans to run every batch the same way is not.

• 1
  Machine class is named3-axis, 4-axis, 5-axis, mill-turn. Not just "CNC".
• 2
  Fixture approach is describedSoft jaws, vacuum, sacrificial tabs, or a custom micro vise.
• 3
  Inspection method is statedVision system, CMM, or optical comparator, not calipers.
• 4
  Material lead time is separatedStock time is on the quote, not hidden in the machining line.

Micro CNC is not always the right process. If the part has no tight tolerance, no fine feature and no need for a specific metal, other processes will be cheaper and faster. A small plastic bracket at ±0.1 mm is often better in 3D printing or vacuum casting, especially in low volumes. The tooling cost and setup time for micro machining do not pay back on a part that does not need the accuracy.

Geometry also rules some parts out. Very thin, flat plates under 0.2 mm thick are hard to clamp without bending. Long thin shafts with a diameter under 1 mm and a length over 20 mm will deflect during turning unless the shop uses a guide bushing or runs the part between centers with light passes. If the design has no room for a support, the process may not be feasible at the tolerance you want.

Deep micro holes are another limit. A 0.3 mm hole at 10:1 depth-to-diameter is at the edge of what drilling can hold. EDM or laser drilling may be the better route. A shop that tells you this up front is more useful than one that quotes it as routine.

The honest answer: micro CNC wins when the part needs metal, tight tolerance and a real 3D shape. When it needs only one of those, check the alternatives first.

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  No tight tolerance needed3D printing or vacuum casting is usually cheaper below 100 pieces.
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  Thin flat platesUnder 0.2 mm thick, clamping forces will bend the part.
• 3
  Very deep small holesBeyond 10:1 depth-to-diameter, consider EDM or laser.

Material choice at micro scale is about machinability and stability more than strength. Aluminum 6061-T6 and 7075 cut cleanly and hold fine detail. They are the default for micro housings, manifolds and optical mounts. Stainless 303 and 316L machine well but work-harden, so light passes and sharp tools matter more than on a larger part.

Titanium Ti-6Al-4V and Inconel are used for medical implants and aerospace micro parts. Both generate heat at the cutting edge and have low thermal conductivity. A 0.5 mm tool in Ti-6Al-4V needs lower surface speed and more coolant than the same tool in aluminum. If a shop quotes the same cutting parameters for both, ask why.

Copper and brass are common in micro electronics and RF parts. C101 and C110 copper are gummy and tend to form built-up edge, so they need higher rake angles and polished flutes. Beryllium copper machines well but the dust is a health hazard, so the shop must control chips and coolant.

On finishes, anodizing adds 5–15 μm per surface. On a part with a 0.5 mm slot, that growth closes the gap. Say the finish before the final dimensions are set, or the anodize will move the part out of tolerance. Laser marking on micro parts is limited by a minimum character height of about 1.5 mm, so plan marking areas with that in mind.

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  Aluminum 6061-T6 / 7075Default for micro housings and optical parts. Cuts clean, holds detail.
• 2
  Stainless 303 / 316LWork-hardens. Light passes, sharp tools, no dwell.
• 3
  Ti-6Al-4V / InconelLow thermal conductivity. Lower speed, more coolant.
• 4
  Copper C101 / C110Gummy. Higher rake, polished flutes, watch built-up edge.

Lead time for micro parts is usually set by the first article, not the run. Once the fixture and program are proven, small parts run fast. The slow part is the setup, the first-article inspection and any tolerance adjustment. A shop that can quote and return a DFM in 12 hours and start production within 24 hours is compressing that front end, which is where most of the waiting happens.

MOQ is a real screen. Many shops set a minimum of 50 or 100 pieces because the setup cost is the same for one part or one hundred. A shop with no MOQ can take a single prototype and then scale to 10,000+ without changing the process. That continuity matters, because re-qualifying a part at a new shop resets the learning curve.

Confidentiality is often the last thing buyers ask about and the first thing they regret not checking. Micro parts frequently sit inside a new product, and a drawing can carry more design intent than a full assembly. Ask for an NDA before you upload. Secure upload and a signed NDA are standard at GreatLight on request.

Delivery performance is worth asking about in numbers, not promises. A shop that tracks its own late-delivery rate and can quote it is measuring the process. GreatLight keeps that figure below 2% historically. Treat that as a process signal, not a guarantee for your specific order.

• 1
  Quote and DFM in 12 hoursFront-end speed is where micro projects usually lose days.
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  Production start within 24 hoursOnce the drawing and DFM are agreed.
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  Parts ship in 3–5 daysFor proven micro parts with a standard finish.
• 4
  NDA on requestAsk before uploading, not after the quote.

The first mistake is treating micro work as a size category. Buyers often search for a shop that "does small parts" and then compare prices. Size is the least useful filter. Tolerance, feature geometry and inspection capability are the filters that predict whether the part will pass incoming inspection.

The second is quoting from a STEP file with no tolerance notes. A neutral model carries no information about what matters. The shop will guess, usually by applying a general tolerance block. On a micro part, a general block of ±0.1 mm can be 5% of the part width and will not match your intent.

The third is accepting a first-article report on one piece for a run of thousands. Micro processes drift: tool wear shows up in the first 20 parts, and thermal drift shows up over a shift. Ask for in-process checks at a defined interval, not only a final inspection.

The fourth is ignoring the finish step until the end. Deburring a 0.3 mm cross-hole by hand can round the edge by 0.05 mm. That is a functional change. Decide the deburr method at the quote stage.

The fifth is picking a supplier on price alone. A cheaper quote that misses the tolerance costs a full rework cycle. At micro scale, rework often means remaking the part, because there is no material left to take another pass.

• 1
  Filtering by size, not toleranceSize tells you little. Tolerance and geometry tell you everything.
• 2
  No tolerance notes on the modelThe shop will apply a general block that may not fit a micro part.
• 3
  One-piece first article onlyAsk for in-process checks at a defined interval.