How to Outsource CNC Machining to China, Step by Step

To outsource CNC machining to China is not to mail a STEP file into the void and hope. Done properly, it is a structured transfer of a manufacturing work package: you define the part, the tolerances, and the acceptance criteria; the factory machines, inspects, and ships against that definition. The buyers who succeed treat it as an engineering process. The ones who get burned treat it as an online purchase.

The market splits into three kinds of suppliers: platforms that broker your job to the cheapest available shop, trading companies that add margin and a layer of telephone, and real factories that machine in-house. This guide is written for working with the third kind — the CNC machining services in China that quote from their own machines, their own programmers, and their own inspection room.

Ninety percent of outsourcing problems are born in the RFQ. A factory can only hold what you define. A complete package contains a 3D STEP file for programming and quoting, a 2D PDF drawing with tolerances, threads, and critical dimensions called out, the material and grade (not just aluminum — 6061-T6 or 7075-T651), the finish with a spec reference such as MIL-A-8625 Type II, and the quantity break you want priced — for example 1, 10, 100, and 1,000 pieces.

Before you send anything, run your design past DFM rules: relax tolerances that do not carry function, avoid deep narrow pockets, and standardize corner radii. Our DFM design guide covers the specific rules that cut machining cost. Ten minutes of DFM review routinely saves more than a week of supplier negotiation.

The unit price is the least comparable number in the quotes you receive. Build a landed-cost line for each candidate: part price at your real quantities, tooling or setup if any, surface finishing, inspection documentation, packing, freight at the quoted Incoterm, and import duty for your HTS code. Only then compare. The cheapest unit price frequently carries the most expensive extras.

Understand what is driving each number before you negotiate. Machine time dominates, and it is driven by part complexity, material, and tolerance grade — which is why DFM changes beat haggling every time. For a component-by-component breakdown with worked examples, see our guide to CNC machining cost.

For prototypes and urgent batches, air freight at 3–7 days door to door is the default and the cost is modest at prototype weights. For production volumes, sea freight at 3–5 weeks cuts freight cost per part to cents. Quote DAP or DDP so the supplier handles export documentation and you receive parts at your dock; under DDP the supplier also covers import duty, which makes landed cost fully predictable.

Build the shipping leg into your schedule from the start rather than discovering it at the end. Realistic totals and the quantity thresholds where each mode makes sense are laid out in our guide to lead time and MOQ.