Most of what you can read about machining in Vietnam is about the supply side: which shops have five-axis centres, which claim a hundredth of a millimetre. Very little of it is about the moment where machined-parts orders actually go wrong — the parts arrive, both sides measure them, and one says “in tolerance” while the other says “out”.
That argument is almost never about the skill of the machinist. It is about what the drawing left unsaid, and what nobody agreed about how the parts would be measured. This article lists what to settle before you ask a Vietnamese shop for a price, so that the quotation, the parts and the inspection all refer to the same thing.
💬 Want a second pair of eyes on a drawing before it goes out to quotation? Send it to us and we will point out what a Vietnamese shop is likely to ask about.
Why does a drawing that works at home fail abroad?
A drawing used with a long-standing supplier relies on unwritten house standards; a new supplier fills every gap with its own standard, and the gap becomes a dispute at inspection.
Chamfer sizes, burr limits, which face is the reference, how a bore is measured — these settle into habit between a buyer and its regular shop. Send the same drawing to a new supplier in another country and those habits disappear. The supplier does not refuse the drawing; it fills the gaps with what it normally does, and quotes on that basis. The remedy is to remove the gaps before quotation, not to argue about them after delivery.
The eight points to settle before you ask for a price
If these eight points are on the drawing or in an attached note, every shop quotes the same part; whatever is missing is decided by the shop.
| Point | How to state it | What happens if it is missing |
|---|---|---|
| General tolerance class | Standard and class in the title block | Untoleranced dimensions are left to the shop |
| Geometric tolerances and datums | Feature control frames with datum references | The reference face changes with each measurement |
| Fits | Fit symbol plus the numerical limits | Two readings of the same symbol |
| Surface finish | Parameter, value and measurement conditions | Finish judged by eye and not reproducible |
| Edges and burrs | A note covering all unspecified edges | Deburring left out of the quotation |
| Material and substitution | Standard and grade, composition or properties, substitution rule | Same name, different material |
| Heat treatment and coating | Process, hardness, thickness, which surfaces | Nobody owns the dimensional change |
| Inspected dimensions and quantity | Balloon numbers, instrument and sample size | Full inspection or sampling changes price and lead time |
The last line moves price and lead time more than any other. Measuring every part on a coordinate measuring machine and spot-checking key dimensions with hand gauges are very different amounts of work, and two shops assuming different plans will quote very different prices.
General tolerances: name the class or the shop chooses it
Dimensions without an individual tolerance take the general tolerance named in the title block; if no class is named, the shop decides how loose they can be.
ISO 2768-1 sets general tolerances for linear and angular dimensions in four classes — fine (f), medium (m), coarse (c) and very coarse (v). Writing “ISO 2768-m” in the title block fixes the limits for every untoleranced length.
The geometric half of that standard has changed. ISO 2768-2, which gave general geometric tolerances in classes H, K and L, was withdrawn in 2021, and ISO 22081:2021 now covers general geometrical specifications. Many drawings still cite “ISO 2768-mK”. A shop may read that the way you intend, but it rests on a withdrawn standard. Where flatness, perpendicularity or straightness matters, write the value in a feature control frame rather than relying on a general class.
Datums, fits and surface finish
A geometric tolerance without a datum cannot be measured the same way twice, a fit symbol without its numbers invites a second reading, and a roughness value without its conditions is a guess.
The most common omission is the datum. Parallelism or perpendicularity “to what” has to be on the drawing; otherwise the inspector places the part on whichever face sits most easily, and the result depends on who measures. Define datums the way the part is located in assembly.
Fit symbols under ISO 286 travel well internationally, but writing the upper and lower limits beside the symbol removes a round of questions and a chance of misreading.
Surface texture standards have also moved: the ISO 21920 series, published in 2021, replaced ISO 4287 for profile parameters. Whichever edition your drawing follows, state the parameter (Ra, Rz), the value and the measurement conditions such as cut-off, so the shop can measure what you will measure.
💬 We can check a drawing package against what Vietnamese machine shops will need, then run the quotation round on your behalf — see sourcing from Vietnam, or send us the drawing.
Material: a grade name is not enough on its own
“Equivalent” grades across standards are close, not identical, so write the standard and grade, the composition or properties that matter, and whether a substitute is allowed.
A practical local point: Vietnamese machine shops and material stockists work extensively with Japanese drawings, and their price lists and stock are commonly described in JIS designations — S45C carbon steel, SUS304 stainless, A5052 or A6061 aluminium, SKD11 tool steel. If your drawing calls for an EN or ASTM grade, a shop will often propose “the JIS equivalent” from stock. That may be perfectly acceptable, but it should be your decision.
The grades are not interchangeable by name. JIS SS400, for example, is specified mainly by tensile and yield strength, while the grades usually quoted as its equivalents, ASTM A36 and EN S235JR, set limits on chemical composition that SS400 does not. So the specification should carry three things:
- Standard and grade, with the standard number, not only the grade name.
- The properties that matter for the part — composition limits, tensile strength, hardness — so the requirement is understood even where the grade name is not.
- The substitution rule — whether an equivalent is accepted, and whether it needs prior written approval.
Also ask whether the material is held in stock locally. A grade that has to be imported adds its own procurement time before the first chip is cut; see planning production lead time in Vietnam.
Heat treatment and coating
Any process that changes the part after machining — hardening, anodising, plating, painting — needs its own line on the drawing, because it changes dimensions and is often done by another workshop.
State the process, the target (hardness and scale, coating thickness), which surfaces are treated or masked, and whether dimensions on the drawing apply before or after treatment. Heat treatment and surface finishing are frequently subcontracted in Vietnam. That is normal, but it should be disclosed, and the returned parts should be inspected by someone before assembly or shipment. What to check on a first visit to a Vietnamese factory covers how to ask which steps leave the building.
Agree how the parts will be measured
The same feature measured with different instruments gives different answers, so agree what is measured, with which instrument and on how many parts, at the quotation stage.
| Instrument | Suited to | Datum reproducibility | What to agree in the quotation |
|---|---|---|---|
| Calliper | Outline and depth dimensions | Depends on how it is held | Which dimensions it may be used for |
| Micrometer, bore gauge | Diameters and thicknesses | Limited to the measured faces | Which dimensions require it |
| Coordinate measuring machine | Position, flatness, profile and other geometric tolerances | Datums can be defined in the program | Which dimensions, how many points, how many parts |
Balloon every dimension on the drawing and attach an inspection plan: which balloon is measured with which instrument, and how many parts per lot. Ask for a calibration record for the instruments that measure your critical dimensions.
For the first lot, there is no need to invoke an aerospace first-article standard such as AS9102 for a general machined part. A contract line saying “the first lot is measured on every characteristic and the report is attached” achieves what you need. Sampling for later lots is covered in pre-shipment inspection and AQL.
Write the acceptance rules down before the first lot
Most acceptance disputes are not about whether a document exists but about what counts as a pass, so write the acceptance rules into the order before production.
Agree in writing:
- The acceptance basis. The drawing tolerances, or a separate acceptance specification.
- The material certificate type. Under EN 10204, a type 3.1 inspection certificate reports results from the actual material lot, while a type 2.2 test report reports non-specific results. Say which you need; the difference is explained in quality documents to request from a Vietnamese parts supplier.
- Non-conforming parts. The order of remedies — rework, replacement, credit — and who pays for each, including freight.
- Transit damage and corrosion. Packing and rust-prevention requirements, and where responsibility passes.
- Corrective action reporting. The deadline and the format.
Written in advance, these rules turn a rejection into a discussion of how to fix it rather than who is at fault. What to do when a lot is rejected anyway is covered in defects and delays from a Vietnamese supplier.
The achievable tolerance, the price and the lead time all depend on the part’s geometry and on the machines and metrology each shop actually has. The surest way to know is to run your own drawing through a trial lot.
💬 If you would like the trial lot measured and the report checked in Vietnam before parts ship, tell us about the part.
Frequently asked questions
1. Can I send my existing drawings unchanged?
The geometry and symbols will be understood. What will not travel is anything that relied on your house standards — unspecified edge breaks, burr limits, the reference face, the inspection habit. Add those to the drawing or an attached note first.
2. Does the drawing need to be translated into Vietnamese?
Dimensions and symbols do not. Notes should be in clear English at least, and the notes on material, heat treatment, coating and inspection are the ones where a mistranslation becomes a non-conformance. Keep them short and specific.
3. How tight should my tolerances be?
Only as tight as the function requires. Tight tolerances on non-functional features raise cost, lengthen lead time and reduce yield without improving the part. What each shop can hold depends on its machines and its measuring room.
4. Should I ask for CMM reports on every lot?
For the first lot, measuring every characteristic is reasonable. After that, a sampled report on the critical dimensions is usually enough, with full measurement repeated after any change of tool, material lot or process.
5. The shop proposed a JIS material instead of my EN grade. Should I accept?
It may be fine. Compare composition and mechanical properties with your requirement, check whether your customer’s specification allows it, and then approve it in writing for that part number, so the next lot cannot change it without approval.
Sources: ISO 2768-1; ISO 2768-2 withdrawn and replaced by ISO 22081:2021; ISO 286; ISO 21920 series replacing ISO 4287; EN 10204; AS9102. Checked on 17 October 2026.