industrial, machinery and appliance spare parts / Buying guide
CNC machining from China
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Chinese machine shops are numerous, fast and cheap, and they will make exactly what the drawing says. That last part is the whole discipline: a drawing that leaves something unstated will have it decided for you, in the direction that costs least.
The parts of a quote worth arguing about are tolerance, material grade and finish. The per-piece price is usually the least interesting number on the page.
In this guide
What to send
- STEP files for geometry — universally accepted and unambiguous.
- A dimensioned PDF drawing alongside it, carrying tolerances, material, finish and any critical callouts. Geometry alone does not carry intent.
- Quantity, including whether this is a one-off or the first of a repeating order — it changes how the shop approaches fixturing.
- A reference sample if one exists, which settles more questions than any drawing.
Tolerance conventions to state explicitly
Name the general tolerance standard you expect and the specific tolerances that matter. Left unstated, a shop will apply its own house general tolerance, and it will not be the tightest one available.
Mark which dimensions are critical. Three to six per part is normal. Marking everything critical is the fastest way to double a quote and lengthen a lead time for no benefit.
Material substitution is the common surprise
Chinese material designations differ from Western ones and equivalents are approximate. 304 and 201 stainless are frequently interchanged; aluminium grades likewise. State the grade you require and ask for a material certificate on anything structural.
If you accept an equivalent, get the actual grade in writing rather than the word "equivalent". The difference shows up as corrosion or fatigue months later, long after the invoice.
Finish, which is priced separately and often assumed
- As-machined is the default and carries visible tool marks.
- Bead blasting, anodising, plating, passivation and powder coating are each separate operations with their own cost and lead time.
- Anodising colour varies between batches; if colour matters, specify it and expect a sample round.
- Deburring is not automatic. Say so if edges matter.
Questions & answers
Common questions
- How long does a machined part take?
- Simple parts, 5–10 days plus freight. Complex or finished parts, two to three weeks. Sampling adds a week.
- What quantity makes it worth it?
- Even one, if the alternative is an OEM price. The setup dominates below about twenty pieces, so ordering a few spares at the same time is nearly free.
- Do I get a material certificate?
- On request, and you should ask for anything structural or heat-treated. It is normal and it is cheap.
Your next step
Have a link you want checked?
Send a 1688 or Taobao product link and you get back the specification in English, the supplier check, and the landed cost to your country before you commit to anything.
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