What tolerance can a CNC machine hold?

A general machined feature holds around plus or minus 0.05 mm as standard. Precision features reach plus or minus 0.02 mm, and features that are specifically reviewed for it can reach plus or minus 0.005 mm or tighter. The achievable value depends on material, geometry, feature size and how the feature is measured, so it is agreed per part rather than quoted as a single number.

How long does CNC machining take from China?

Around three weeks from drawing approval for regular CNC projects is a realistic planning figure. Simple prototypes can take about a week when material is in stock, and complex parts with tight tolerances and special finishes take four to six weeks. Freight time to Europe or the US is additional.

Why is my CNC quote higher than expected?

The usual causes are the amount of material removed, the number of setups, tolerances tighter than the function requires, hand finishing, and full dimensional inspection. Quantity also matters because programming and setup are spread across the batch. Reducing setups and tightening only functional features usually cuts cost more than negotiating the unit rate.

What documentation should I ask for with machined parts?

At minimum a dimensional inspection report and a material certificate with heat number. For regulated products, add a first article inspection report, a PPAP package if your process requires it, and a certificate of conformance. Agree the exact documents and format at quotation stage, because certificates take time to obtain.

Can I order a single prototype part?

Yes. One part is accepted, and prototype quantities are normal work. A first article is also the cheapest way to verify that a supplier holds the tolerances your drawing actually needs.

What happens if parts arrive out of specification?

Non-conforming parts are reworked or remanufactured at the supplier's cost, and the root cause is traced so the next batch does not repeat it. That commitment should be written into the purchase order rather than assumed.

Do I need a 2D drawing or is a 3D model enough?

A STEP model defines geometry but not tolerance, finish or material condition, so a model alone results in general tolerances being applied. Send the model with a drawing, or at minimum a list of critical dimensions and how they will be measured.

How do I verify a Chinese CNC supplier is reliable?

Check the certificate numbers rather than the scanned documents, ask which machines will run your part, ask for the inspection plan, and speak to a reference customer in your industry. Then place a small first order and measure every feature before committing to production volume.

CNC Machining FAQ: Answers for Buyers and Engineers

Most questions we get from engineering and purchasing teams are the same ten, and the honest answers are more useful than the marketing ones. Below is what we tell a buyer on a first call, including the parts that are inconvenient.

What tolerance can you actually hold?

Tolerance is a cost decision before it is a manufacturing decision. On a typical machined feature, these are the bands we work in:

Band	Typical use	What it does to cost
±0.1 mm	Brackets, covers, non-mating surfaces	Baseline. Fast to make, easy to inspect.
±0.05 mm	General machined parts, most mating features	Small increase. Standard for us.
±0.02 mm	Bearing seats, locating features, alignment	Needs a stable setup and a capable machine.
±0.005 mm and tighter	Spindles, sealing faces, optical mounts	Temperature control, slower passes, more inspection, more scrap.

The number on its own means little. What matters is whether the feature can be measured, whether the setup is rigid, and whether the material moves after machining. We have produced components to ±0.002 mm, but that is a capability on specific features after review, not a blanket specification for every part.

If you put ±0.01 mm on every dimension, you are paying for precision on faces that do not need it, and you make the drawing harder to inspect. Tighten only the features that carry function.

Why a tight tolerance sometimes fails anyway

Three causes account for most out-of-tolerance parts: the datum scheme does not match how the part is set up, thin walls deflect under clamping, or the material is stress-relieved after the first operation and moves before the second. All three are problems with the drawing or the process plan, not with the machine. They are cheaper to fix before the first chip than after the last one.

How long does a CNC order take?

For regular CNC projects, three weeks from drawing approval is a realistic planning figure. That is a reference, not a commitment: material availability, geometry, quantity, finishing and inspection all move it.

Prototype, simple part: about one week if the material is in stock.
Regular production batch: about three weeks.
Complex geometry, tight tolerance, special finish: four to six weeks.

The delays we see most often are not machining time. They are drawings that contradict themselves, a finish specified as “as machined” when the part needs anodising before assembly, material that has to be imported, and a first article that sits unapproved for a week. Clear documents at the RFQ stage remove most of that.

What actually drives the price of a machined part?

Cost driver	Why it matters	How to reduce it
Material removed	Cycle time scales with volume cut away	Reduce pocket depth, allow a near-net blank, or choose a casting for large volumes
Number of setups	Every refixture risks error and adds handling	Design for access from fewer sides; a 5-axis part can avoid three setups
Tolerance	Adds passes, slows feeds, adds inspection	Tighten only functional features
Surface finish	Hand polishing and coating add days and labour	Specify Ra only where it is needed
Quantity	Programming and setup are amortised over the batch	A second batch of the same part is cheaper per unit than a first
Inspection scope	Full dimensional reports and FAI add engineering time	Agree the sample plan and characteristics in advance

Unit price alone is a poor comparison between suppliers. A quote that excludes finishing, inspection, packaging or freight is not a cheaper quote, it is an incomplete one. Ask each supplier to price the same scope, or the comparison tells you nothing.

Which materials do you machine?

Aluminium (6061, 7075, 5083), carbon and alloy steel (1045, 4140), stainless (303, 304, 316L, 17-4PH), brass and copper alloys, titanium (Grade 5), and engineering plastics including POM, PEEK, ABS, PC and PTFE. A full list with grades and typical finishes is on the materials page.

For anything going into a regulated product, tell us at RFQ stage which material certificate you need. A mill certificate with heat number, chemical composition and mechanical properties takes time to obtain and should be priced with the order, not requested after delivery.

How do you handle a part that comes out wrong?

Every workpiece is checked dimensionally and visually during and after production, and ongoing production is inspected at two-hour intervals. When something does not conform, the part is reworked or remade at our cost, and the cause is traced so the next batch does not repeat it. What we do not do is ship it and hope the customer does not measure it.

What documentation comes with an order?

Every order can include a dimensional inspection report and a material certificate. First article inspection reports, PPAP packages and certificates of conformance are available when agreed at quotation. The full list, and what each document actually contains, is on the documentation page.

The important part is agreeing the documentation before the PO, not after. If your quality team needs a specific report format, send the template with the RFQ.

Can you work from a 3D model without a drawing?

We can, but the result will only be as defined as the file. A STEP model carries geometry, not tolerance, surface finish, material condition or critical feature intent. Without a drawing we apply general tolerances, and a part that is geometrically correct can still fail your incoming inspection.

If a drawing is genuinely not available, send the model plus a short note listing the critical dimensions and how they will be measured. That note is enough to build an inspection plan from.

How do I check a supplier before placing an order?

Ask for the certificate numbers and verify them, not just the scanned PDF. Ask which specific machines will run your part and what the inspection plan is. Ask for one reference customer in your industry and call them. Then place a small first order and measure everything.

A supplier who cannot answer the machine question or the inspection question is selling capacity, not capability.

Frequently asked, briefly

Do you have a minimum order quantity?

One part is accepted. Prototype quantities are normal work for us, and they are also how most long-term customers start.

Can you ship to Europe and the US?

Yes. EXW, FOB or delivered duty paid, depending on what your forwarder prefers. We will quote the Incoterm explicitly so there is no surprise at customs.

Can you sign an NDA before I send drawings?

Yes, and we would rather sign one than receive a drawing you are uncomfortable sending. Ask for it in the first email.

What file formats do you accept?

STEP, IGES, X_T, SLDPRT, DWG, DXF and PDF, up to 20 MB per file. ZIP archives are fine for multi-part assemblies.

Do you do assembly and finishing?

Finishing is done in-house or with named partners, and it is quoted as a line item so you can see what it costs. Assembly is available on request.

Have a drawing you want a straight answer on?

Send it through the quote form and an engineer will reply with the process, the tolerance we can hold on your critical features, and what documentation we can supply. If the part is a bad fit for us, we will say so.