How AQL tables work and how to set an inspection level that catches real problems.
This is written for buyers and design engineers rather than machinists. It covers what to put on the drawing, what it costs, and the mistakes that turn a straightforward part into an expensive one.
The rules that matter
- AQL 1.0 with general level II is a common default
- Accept and reject numbers come from the lot size, not the sample
- Critical defects should be AQL 0
- AQL is a sampling plan, not a guarantee of quality
Common mistakes
- Applying AQL to a 20-piece order
- Using AQL 2.5 for a safety-critical feature
Both of these are cheap to fix at the drawing stage and expensive to fix after the parts are cut. If you are unsure which side of the line your design is on, send it over before you release it.
How this shows up in a quote
A quote is built from material, machine time, setup, finishing and inspection. Anything that adds a setup, a secondary operation or a tighter inspection method moves the number. When we quote, we show the process route, so you can see which requirement is driving the price and decide whether it is worth keeping.
Frequently asked questions
Does this apply to both milling and turning?
Yes. The principles are the same. Turning is usually cheaper for concentric geometry and milling for prismatic geometry, but the tolerance and finish rules carry across both.
What is the cost of getting this wrong?
Usually one extra setup, one extra operation or a scrapped batch. In practice, fixing it at the drawing stage costs nothing; fixing it after the first article costs a week and a re-quote.
Can you review my drawing before I release it?
Yes, and we would rather do that than quote a design that is going to be expensive. Send the STEP file and drawing and we will come back with DFM comments alongside the price.
Do you work from a PDF drawing or do you need CAD?
We need a STEP file for the geometry and a dimensioned PDF for the tolerances. A PDF alone is not enough for anything with curved surfaces.
Related pages
- Guides — the full index for this section.
- Rework, Warranty and Non-Conformance Handling
- Building a Second-Source Machining Strategy
- RoHS and REACH Compliance for Machined Parts
- GD&T Basics for CNC Machining Buyers
- Instant CNC quote
- Tolerance quick reference
- Frequently asked questions
Get a price for your part
Send a STEP file and a drawing with tolerances, material and quantity. We quote within one working day and machine in our own facility in Shenzhen — milling, turning, EDM, grinding and finishing under one roof, no trading middleman.
Start an instant quote or send your drawings directly. English-speaking engineering support, DFM feedback before you commit to a batch.