The scale of the claim
A micron is a thousandth of a millimetre. When a machine shop says it holds ±5 microns, it is claiming that a dimension on a finished part will sit within 0.005 mm of the number on the drawing — every time, across a production run. To grasp how small that is, consider that metal itself will not sit still at this scale: aluminium expands by roughly 23 microns per metre for every degree Celsius of temperature rise. A one-metre part machined perfectly at 25°C is out of a ±5 µm tolerance by lunchtime if the workshop warms by half a degree. That is why micron-level machining is less about the cutting tool than about everything around it — temperature-controlled rooms, machine calibration, and measurement good enough to prove the claim. For a buyer, understanding tolerances is understanding what you are actually paying for.
The grades: from “general” to grinding
Most engineering drawings do not tolerance every dimension individually; they invoke a general standard. ISO 2768 covers untoleranced dimensions in classes — for a 50 mm feature, the “fine” class allows ±0.15 mm — and ordinary fabrication and general machining live here, at a tenth of a millimetre or looser. ISO 286 takes over where fits matter, grading tolerance bands from IT01 (finest) to IT18 (coarsest): conventional CNC machining typically delivers the mid grades, tight-toleranced machining reaches around IT6–IT7, and the finest grades belong to grinding, honing and lapping rather than milling. The practical ladder for a buyer is simpler than the standards suggest: about ±0.1–0.2 mm is routine work any competent shop can quote; ±0.025 mm (25 microns) marks a genuine precision shop; below ±0.01 mm is a different discipline, with different machines, metrology and prices.
When microns matter — and when they do not
Tolerance is a functional requirement, not a virtue. Microns matter where parts must fit and move — bearing seats, press fits, sliding spools in hydraulic valves; where interfaces seal or align — semiconductor-equipment components, where a stage a few microns out of position ruins a wafer; where regulation demands it — machined implants and surgical instruments; and where assemblies stack — ten parts each ±0.05 mm can accumulate half a millimetre of error. Conversely, brackets, covers, enclosures and frames function identically at ±0.2 mm and ±0.02 mm; the only difference is the invoice. The classic specification error is copying a tight tolerance across a whole drawing “to be safe”. Every micron of unneeded precision is paid for on every part, forever.
Why cost climbs a curve, not a line
Tightening a tolerance does not add cost linearly — it steps it upward. Each step down the ladder forces slower feeds and extra finishing passes (machine time), better and more frequently calibrated machines (capital), climate control (facilities), more inspection — at micron level, coordinate measuring machine (CMM) time can rival cutting time — and higher scrap, because more good-faith parts now fall outside the band. Industry guidance is blunt on the point: specify the loosest tolerance that still meets the part’s function, because unnecessarily tight tolerances significantly raise cost and stretch lead times. A useful buyer’s habit is to ask the shop where the price steps are. A good machinist can often tell you that ±0.05 mm costs little more than ±0.1 mm on your part, but ±0.01 mm doubles the inspection burden — information that should flow back into the design.
How to read a machinist’s capability claims
Capability claims reward careful reading, because three different numbers hide behind “we do microns”. Positional accuracy is how close the machine puts a feature to its nominal location; repeatability is how tightly it returns to the same position again and again; a best-achieved tolerance is what happened once, on one material, on a good day. The honest caveat is that machine-tool brochure figures are not shop capability: a machining centre specified at 5 microns will not deliver 5-micron parts in an uncontrolled workshop, on tall thin-walled parts, or in materials that move as they are cut. What separates a claim from a capability is proof — CMM reports against the drawing, process capability on production runs, and certifications (ISO 9001 as the floor; AS9100 or ISO 13485 where aerospace or medical work is involved) that audit the system behind the number.
Singapore’s record shows what properly stated claims look like. Beyonics, a contract precision manufacturer in Marsiling, states its machining capability as 8 µm positional accuracy and 4 µm repeatability in aluminium, magnesium and specialty alloys — accuracy and repeatability quoted separately, materials named, with ISO 9001, IATF 16949 and ISO 13485 behind it. Shine Precision Engineering states ±0.025 mm across 3-, 4- and 5-axis milling and turning in more than 50 materials including titanium, Inconel and PEEK, across 50-plus CNC machines. Both claims tell a buyer exactly what to expect and on what evidence.
What to put on the enquiry
The efficient enquiry names the material, the critical dimensions and their tolerances (and leaves the rest at general tolerance), the quantity, and the proof required — a CMM report, a first-article inspection. Shops price uncertainty; precision in the enquiry buys precision in the quote. Singapore’s machining base — the wider context is in the precision engineering article — is deep enough that the question is rarely whether a tolerance can be held here, but which shop holds it as routine capability rather than heroic effort. The shops, with their stated capabilities, are on the CNC machining and precision machining pages.