Quality and inspection

How we control quality on CNC parts

Parts are made in partner machine shops in China. Our team manages each order and inspects the parts before they ship. Quality control is not one check at the end; it is four checkpoints, each placed where a mistake is cheapest to fix.

1. Drawing review before the quote.
2. First-article approval before the batch.
3. Dimensional inspection of finished parts, recorded in a report.
4. Cosmetic check and packaging before the box is sealed.

1. Drawing review

Most quality problems start as ambiguity in the drawing: a tolerance that is missing, a thread with no class, a finish without a color, a datum that cannot be fixtured. An engineer reads your drawing when quoting and raises these questions in the DFM notes, before any metal is cut.

We also check that the tolerances are achievable with the chosen process and material. Our standard tolerance is ±0.03 mm. Tighter tolerances on critical features are possible when called out on the drawing, and we confirm them in the quote. If a callout is unusually tight for its function, for example ±0.01 mm on a clearance hole, we will suggest relaxing it, because tighter tolerances cost machine time and inspection time. The CNC machining tolerances guide explains what is practical by feature.

2. First article inspection

Before the full batch runs, the first part off the machine is measured. You receive photos and the measured values of the critical dimensions. Production continues only after you approve.

This matters most for low-volume production. A setup error caught on part one costs a single part; the same error found on delivery costs the whole batch and two weeks. For a single prototype, the first article is the order itself, and it is covered by the inspection report.

If the first article shows a problem, the setup is corrected and a new first article is shown to you. If the first article reveals a problem in the design rather than the machining, you can revise the drawing at this point and we will re-quote if the change affects cost.

3. What a CNC inspection report contains

Every order ships with an inspection report. It is a record of what was measured, not a certificate of conformity issued without data. A typical report includes:

Measuring methods depend on the feature. Typical instruments are:

• Calipers for general linear dimensions in the ±0.03 mm range and looser.
• Micrometers for outside diameters and thicknesses with tighter tolerances.
• Height gauges on a surface plate for step heights and hole positions from a datum.
• Pin gauges for hole diameters, go/no-go on fits like H7.
• Thread gauges (plug and ring) for internal and external threads.
• CMM on request when the drawing calls for it, for example for GD&T position, profile or flatness callouts that hand tools cannot verify reliably.

Mark your critical dimensions on the drawing (a balloon or a note such as "CTF" works). Those are the features we measure and report. If you need every dimension measured, or a specific sampling plan for a batch, say so in the request and we will include it in the quote.

4. Material certificates

Material (mill) certificates are available on request. A mill certificate traces the stock to the producer and lists chemical composition and mechanical properties for the heat or lot, so you can confirm that 6061-T6 really is 6061-T6. Ask for certificates when you request the quote, because they must be collected when the material is purchased. See materials for the grades we stock and source.

5. Cosmetic standards and packaging

Dimensions are only part of quality. Parts are checked for burrs, sharp edges, tool marks outside the specified finish, handling scratches and dents, and finish defects such as uneven anodizing color or bare spots. As-machined parts typically have Ra 3.2 µm; if you need a lower roughness or a uniform cosmetic appearance, specify it on the drawing. Our surface finishes page explains what each finish can and cannot hide.

Parts are cleaned and packed so they do not touch each other in transit: individual bags, foam or separators for cosmetic and anodized parts, and protection for threads and precision bores where needed.

Remake policy

If parts are out of tolerance against the approved drawing, we remake them free. The process is simple:

1. Contact us at quote@7dayparts.com soon after delivery with your order number.
2. Send photos of the parts and the measurements that are out of tolerance, with the method you used.
3. We compare your data with our inspection report and the approved drawing.
4. If the parts do not meet the drawing, we remake them at no charge and ship the replacements.

The policy covers parts that do not meet the approved drawing. It does not cover features that were not specified, or design changes made after approval. That is why the drawing review and first article come first: they make sure the drawing we inspect to is the one you meant.

We do not claim ISO or other certifications. What we offer is measured data on every order and a clear remake policy.