Micro Machining: A Buyer's Guide to Very Small Precision Parts
Micro machining is the production of very small parts, or very small features on larger parts, with cutting processes adapted to that scale. For a buyer the practical definition is simple: if your part is under about 10 mm overall, or has holes, slots or walls under 1 mm, it needs a shop that runs different machines, tools and gauges than a standard CNC job shop. This guide explains what those are, what tolerances to expect and how to brief a shop so the quotes you get back are comparable.
What counts as a micro machined part
There is no ISO definition of micro machining. Engineers and buyers use the term for two kinds of work:
- Small parts. The whole part fits inside a 10 mm cube, sometimes much smaller. Connector pins, watch pinions, bone screws, fiber ferrule holders, sensor housings.
- Micro features on normal parts. A 40 mm manifold with 0.3 mm orifices, a lens barrel with a 0.2 mm wall, a mold insert with 0.1 mm ribs.
Both share the same problem. The cutting tool gets small and flexible, the tolerance becomes a large fraction of the feature size and the part is hard to hold, clean and measure. That is why size alone does not tell you whether a shop can do the job. The ratio of tolerance to feature size does.
| Part example | Typical size | Smallest feature | Typical tightest tolerance |
|---|---|---|---|
| Connector contact pin | ⌀0.8 x 6 mm | ⌀0.4 mm tip | ±0.005 mm on diameter |
| Orthopedic micro-screw | ⌀1.5 x 8 mm | 0.25 mm thread pitch | ±0.01 mm |
| Fiber alignment housing | 6 x 6 x 10 mm | ⌀0.13 mm bore | ±0.002 mm on bore (specialist) |
| Watch component | ⌀4 x 1.2 mm | 0.3 mm slot | ±0.005 mm |
| Endoscope tip component | ⌀3 x 5 mm | 0.15 mm wall | ±0.01 mm |
Values are typical examples for orientation, not specifications.
The four processes behind most micro parts
Most micro parts are made with one or more of four processes. The geometry of your part decides which, much more than the material. The micro machining process overview covers each one in more depth.
Swiss-type turning. A sliding-headstock lathe feeds bar stock through a guide bushing, so the tool always cuts right next to the support. That makes long, slender turned parts possible: pins, shafts and cannulas with length to diameter ratios of 10:1 or more. Modern Swiss-type machines carry live tools, so cross holes, flats and slots are done in the same cycle. Typical bar capacity for micro work is ⌀0.5 to 12 mm.
5-axis micro milling. High-speed spindles, often 30,000 to 60,000 rpm or more, drive end mills as small as 0.1 mm. Five axes let the shop reach several faces in one setup, which matters because every re-clamp adds a few microns of error. Housings, implants, fluidic chips and optical mounts go here.
Micro drilling. Drills start around ⌀0.05 mm for specialist work, with ⌀0.2 mm a common practical lower limit in production. Holes are drilled in short pecks to clear chips. Depth is usually limited to about 10 times the diameter before cost climbs.
Wire and sinker EDM. Electrical discharge machining removes material with sparks, so there is no cutting force. It makes sharp internal corners, thin slots and features in hardened steel that no end mill can reach. Wire diameters of 0.03 to 0.1 mm are typical.
Typical tolerances and feature sizes
The numbers below are what micro machining shops typically hold in production. They are a starting point for your drawing, not a promise. The tolerance and materials reference has the full table including ISO 286 grades.
| Characteristic | Typical capability |
|---|---|
| Smallest feature (slot, rib, boss) | 0.3 mm |
| Drilled hole | from ⌀0.2 mm |
| Wall thickness | from 0.15 mm, material dependent |
| Linear tolerance, general | ±0.01 mm |
| Linear tolerance, best on selected features | ±0.005 mm |
| Bore and shaft fits | H6 and h5 (IT5 on shafts) |
| Flatness | 0.005 to 0.05 mm |
| Runout on turned diameters | 0.01 mm |
| Surface roughness | Ra 1.6 μm typical, Ra 0.8 μm best |
Two points matter more than any single number.
First, tight tolerances cost measurement time. A ±0.005 mm feature on a 2 mm part cannot be checked with a caliper or even a standard micrometer with confidence. It needs a CMM with a small stylus, a vision system or dedicated gauges, and the part has to be at or near the ISO 1 reference temperature of 20 °C. Every tight feature you add is a feature someone must measure on every sampled part.
Second, the tolerance has to fit the feature. ±0.01 mm on a 0.3 mm slot is about 3 percent of the feature size. The same tolerance on a 30 mm length is 0.03 percent. Shops think in these ratios, and so should the drawing.
Materials that machine well small
Almost any machinable material can be micro machined, but some make life much easier.
| Material | Micro machinability | Typical use |
|---|---|---|
| Brass C36000 | Excellent, short chips | Connectors, watch parts, instrument pins |
| Stainless 303 | Good, free machining | General small parts, fittings |
| Stainless 316L | Fair, gummy, burrs | Medical and food contact parts |
| Titanium Grade 5 | Fair, heat and tool wear | Implants, aerospace fasteners |
| Aluminum 6061 / 7075 | Good, watch for burrs | Semiconductor and optics housings |
| PEEK | Good, holds size better than most plastics | Medical, insulators |
| PTFE | Poor for tight tolerance, creeps | Seals, low friction parts |
Ratings are typical shop experience, not a standard.
If the function allows it, a free-machining grade saves money on every part. If the drawing specifies 316L or Ti-6Al-4V because of biocompatibility, keep it and expect the shop to price burr removal and tool wear in.
What drives the price of a micro part
Material is almost never the main cost. A 3 mm titanium part contains cents of metal. The quote is driven by:
- Setup and programming. Swiss-type setups can take a day. On a prototype run of 10 pieces, setup dominates the unit price.
- Cycle time. Micro tools cut with very light chip loads, so material removal is slow even on high-speed spindles.
- Tool wear and breakage. A broken 0.2 mm drill often means a scrapped part. Shops price that risk in.
- Inspection. For tight-tolerance micro parts, measuring can take as long as machining. Sampling plans and first article reports add more.
- Deburring, cleaning and packaging. Burrs on micro parts are removed by hand under a microscope, by abrasive flow or by electrochemical methods. Parts are often packed individually in trays.
Hypothetical example: a buyer asks for 20 prototype pins in 316L, ⌀1.2 x 9 mm, with a ⌀0.3 mm cross hole and ±0.005 mm on two diameters. One shop quotes on a Swiss-type lathe with a long setup. Another quotes on a CNC lathe with a mill. The second quote may be cheaper at 20 pieces and far more expensive at 20,000. That is why real quantities belong in the RFQ.
How to write an RFQ that gets usable quotes
Most bad micro machining quotes come from incomplete RFQs. Shops either add margin for what they cannot see or quote something different from what you meant. A complete RFQ contains:
- A STEP model and a PDF drawing. Shops program from the model and check tolerances on the drawing.
- Material with grade and standard. “Stainless” is not enough. “316L to ASTM F138” is.
- The smallest feature and the tightest tolerance, stated in the text. This is the first thing a shop checks for feasibility.
- Edge condition. For example “burr-free when viewed at 10x” or “edge break 0.02 mm max”. Without it, burrs become an argument after delivery.
- Surface finish and any coating or passivation.
- Quantities. Prototype, pilot run and expected yearly volume, even if rough.
- Inspection and documents. First article report, material certificates, certificate of conformance and how critical features are measured.
- Delivery terms and target date. EXW from the shop or DDP to your site.
If you are unsure about any of this, send what you have. A good micro machining shop will come back with DFM questions, and those questions are a useful signal of how well it understands the work.
Getting matched with the right shop
Finding a shop is harder than it looks. Many shops list “precision” and “micro” on their websites while running standard machining centers. The machine list, the measuring room and sample parts tell you more than the homepage.
When you are ready to pick a shop, follow our guide to micro machining services.
Micropartz is a matching service, not a machine shop. You send one RFQ with your drawing, material, quantity, tightest tolerance and preferred supplier region. We match it with up to 3 shops that run the processes and measurement your part needs and reply within 24 business hours. You deal with the shops directly and pay no fee. If you have a drawing ready, send an RFQ and compare quotes from shops that actually do this work.
Frequently asked questions
What size parts count as micro machining?
There is no formal cutoff. In purchasing practice it means parts with an overall size under about 10 mm, or larger parts with features under 1 mm, such as holes below 0.5 mm, slots of 0.3 mm or walls of 0.15 mm.
Is micro machining more expensive than normal CNC machining?
Per part, usually yes, even though the material cost is tiny. Cycle time, tool wear, setup, handling and above all inspection take more effort per part. On volume, Swiss-type turning can bring the unit price down sharply.
Can I send a micro part RFQ without a 3D model?
You can, but quotes will be slower and less accurate. Most micro machining shops program from a STEP file and check tolerances on the PDF drawing. Send both if you have them.
What is the most common reason micro parts are rejected?
Burrs and edge condition, followed by features measured with a method the buyer and shop never agreed on. Both are solved on the drawing and in the RFQ, before any metal is cut.
Reviewed against
- ISO 286-1:2010, Geometrical product specifications, ISO code system for tolerances on linear sizes
- ISO 1:2022, Standard reference temperature for geometrical product specification (20 °C)
- Wikipedia: Machining
Numbers in this guide are typical values for orientation. The drawing, the material certificate and the matched shop set the real ones.
Get matched with a micro machining shop
Send your drawing once. We match it with up to 3 shops that fit the part, and reply within 24 business hours. Free for buyers.
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