CNC capacity is everywhere in China. The difference that matters isn't the headline price per hour — it's whether the shop can hold your tolerance, prove it with inspection, and coordinate the secondary operations your part actually needs.
If you source machined parts from China, you've seen the pattern: a shop quotes dramatically lower than a domestic supplier, the first articles look fine, then a batch drifts out of tolerance or a surface finish comes back wrong. This guide covers how to pick the right tier of supplier, what tolerances are genuinely realistic, and where the real cost hides.
Most buyers treat "a CNC shop" as one thing. It isn't:
The failure mode is using a volume shop for a 10-piece prototype (you wait weeks and pay setup for nothing) or a prototype shop for 5,000 pieces (you pay prototype prices and fight consistency).
A shop that writes "±0.01 mm" on a quote isn't the same as one that holds it across a run. Reality:
Use GD&T to control what actually matters — the position of a bore — instead of stacking linear tolerances that fight each other. A drawing that over-tolerances everything gets inspected slowly, scrapped arbitrarily, and quoted defensively.
"Aluminum" is not a material. For a part that has to land in the EU or US, specify the grade explicitly — 6061-T6, 7075-T651, 304L, 316L — and request the mill certificate. Without it you can't prove RoHS compliance for the EU, and you can't defend a failure claim later.
For aluminum and steel stock, remember the US applies Section 232 tariffs on top of the part cost. The duty is on the metal, so the material choice and country of the feedstock both affect the landed number — another reason to pin the grade early.
The machined blank is rarely the finished part. Anodizing, powder coating, heat treatment, threading, laser engraving and assembly each add a handoff. The shop that cuts the metal fastest can still blow the delivery date if it outsources finishing to a vendor it doesn't control.
Coordinating these in one chain — machining, then finishing, then inspection — is the difference between "parts in 10 days" and "parts in 10 days, then lost for two weeks at the anodizer." This is exactly why multi-process coordination matters more than any single machine.
A cheap EXW quote means nothing once freight, insurance, tariffs and your own clearing costs stack on top. A $5 part can become $9 by the dock. Model the true cost before you commit — including the EU duty picture if aluminum is involved — and confirm Incoterms so the number you approve is the number you pay.
I run a DFM and supplier-tier pass before the drawing reaches a shop: picking the right tier, pinning the material grade, and planning the secondary ops so the quote reflects reality. First-article inspection and in-process checks keep the run on spec. Send the drawing; I'll tell you the right process, the tolerance you can actually hold, and the landed cost.
See the four capability domains →
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DFM checklist before you send a drawing →
Send the drawing and target market — I'll return the process, the realistic tolerance and the landed cost.