CNC Processing Services Mud Guide: 7 Checks Before You Order
This guide is for engineers and buyers comparing CNC processing services for a real part. It covers the checks that decide whether a supplier can hold your tolerance, hit your date, and quote in a way you can actually compare.
In this article
- 1
- 2
- 3
- 4
- 5
- 6
- 7
Key takeaways
Which machine class fits your part
Travel figures are for our own machine list. Use them as a screen, then confirm the exact machine before you commit.
| Part feature | Machine class | Why it fits |
|---|---|---|
| Open pocket, one face, ±0.05 mm | 3-axis mill | Single setup, lowest hour rate |
| Four sides, holes on two faces | 4-axis mill | Rotary table Ø400 mm, fewer fixtures |
| Angled faces, one position callout | 5-axis center | One setup, datums stay fixed |
| Shaft with milled flats and threads | Mill-turn center | Turning and milling in one chucking |
| Plate 4,000 mm long | Large gantry travel | 4,000 × 400 × 150 mm envelope |
| Implant-grade 316L, Ra 0.2–0.8 μm | 5-axis + fine finish | Coolant control and light finishing cuts |
| Inconel bracket, thin walls | 5-axis, low feed | Rigid setup limits chatter and heat |
The short version
Pick the supplier that names the machine, the setup count, the inspection level and the certificate address in writing. Price comes after those four are clear.
Tolerance and machine travel: read the drawing before the price
Most quote arguments start with a tolerance callout nobody defined. A drawing that says ±0.005 mm across every dimension is not a realistic job at that price. Ask which features actually need it. A bearing bore, a dowel hole or a sealing face usually does. An outside profile that sits inside a plastic housing usually does not.
The second question is size. A 200 mm bracket on a 5-axis center with a 600 × 600 × 600 mm envelope is routine work. The same tolerance on a 900 mm aluminium plate needs a different machine, a different fixture, and a temperature-stable shop. The number on the drawing is the same. The process is not.
We hold ±0.005 mm (±0.0002 in) where the drawing calls for it, and our fine finishing range reaches Ra 0.2–0.8 μm. That is achievable, but it is not automatic on every feature of every part. Tell us which dimensions are critical and which are reference. The quote gets shorter and more honest when that is clear.
One more screen: check the tolerance against the material. A ±0.02 mm bore in POM behaves differently after a week than the same bore in 6061-T6. If the part is plastic and the tolerance is tight, say so early. We will tell you what the material will do.
Lead time and MOQ: what the numbers really mean
A supplier that advertises fast delivery is telling you about its scheduling, not your part. Ask what happens between the PO and the first chip. Our own sequence is a quotation and free DFM analysis within 12 hours, production start within 24 hours, and parts shipping in 3–5 days. Those figures assume a released drawing and material in stock.
The trap is a rush job with an unfinished drawing. If the model has an undefined thread, a missing corner radius or a tolerance stack that cannot close, the clock stops and nobody tells you. A good supplier flags that in the DFM note instead of cutting a part that will be scrapped.
MOQ is the other half of this. We run from one prototype to 10,000+ part runs with no minimum order quantity. That is useful for a first article, but it does not mean the unit price stays flat. Setup, fixturing and first-article inspection are spread across the batch. Ten parts cost more per piece than a thousand.
When you compare two quotes, ask both to price the same quantity and the same revision. A quote at 10 pieces against a quote at 500 pieces is not a comparison. It is two different jobs.
Certifications and inspection: ask for the scope
ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022 cover different things. ISO 9001 is the baseline quality system. IATF 16949 is the automotive one, and it matters if your part goes into a vehicle program. ISO 13485 is the medical device standard, and it changes how records are kept. ISO 27001 is about information security, which matters when you send CAD files to an outside shop.
A certificate at group level does not always cover the site that machines your part. Ask for the certificate number and the address on it, then match that address to the shipping address on the quote. This takes two minutes and removes most of the risk.
Inspection is the same story. "Inspected" is not a specification. Ask what is measured, on which features, with what instrument, and when. We inspect 100% of parts before shipment, with raw material checks, in-process monitoring and final inspection, and we send reports on request. If you need full dimensional reports on every part, say so at RFQ stage. It changes the price.
For a first article, ask for the report before the batch ships. Fixing a datum error on one part is cheap. Fixing it on 500 parts is not.
Quote scope and confidentiality: the hidden cost lines
Two quotes for the same part can differ by 40% and both be correct. One includes material certificates, anodizing, laser marking and a dimensional report. The other is bare machining, ex-works. Put both on the same scope before you decide.
Watch for these lines. Material grade and certificate. Surface finish callout, since Ra 1.6–3.2 μm as-machined and Ra 0.2–0.8 μm fine finishing are different operations. Heat treatment or stress relief between operations. Finishing such as anodizing, electroless nickel, powder coating or bead blasting. Inspection level. Freight and any duty.
Confidentiality belongs in the same conversation. Uploads to our quote system are secure and confidential, and we sign an NDA on request. If your part is a pre-release product, get the NDA signed before you send the model, not after.
Last item: revision control. Confirm the drawing revision in writing on the quote. Most disputes we see are not about machining. They are about which version of the model was cut.
Step by step: screen a supplier in one day
Work through these in order. Most weak suppliers drop out by step 4.
- 1Send the same package to every supplierSTEP or IGES plus a PDF drawing with the critical dimensions marked. Note the material grade, finish and quantity. Same revision for everyone.
- 2Ask for a DFM note with the quoteA real note names specific features: thin walls, deep pockets, unmarked tolerances, tool reach. A generic cover letter tells you nothing.
- 3Confirm the machine class in writingAsk which machine type will run the part and whether it needs more than one setup. Multi-setup work adds position error.
- 4Check the certificate addressMatch the address on the ISO 9001:2015 or IATF 16949:2016 certificate to the plant that will cut the part.
- 5Compare quotes at one quantityPrice 10, 100 and 1,000 pieces from each supplier. Look at how setup cost falls as quantity rises.
- 6Define inspection before the POState which features get measured and whether you need a report. First-article report on the first batch, at minimum.
- 7Agree on finishing and freightDecide who handles anodizing, plating or coating, and who pays freight. Unpriced finishing is the usual surprise.
Questions buyers ask us
How tight a tolerance can CNC processing services hold on a normal part?
On a rigid setup with the right machine, we hold ±0.005 mm (±0.0002 in) on the features that need it. That is not the same as holding it on every dimension of a 700 mm part.
The practical rule: tight tolerance on a short, supported feature is normal work. Tight tolerance across a long unsupported span, or on a thin wall, needs discussion before quoting.
Is there a minimum order quantity?
No minimum order quantity. We run from one prototype to 10,000+ part runs.
Unit price still depends on quantity, because setup, fixturing and first-article inspection are fixed costs spread across the batch.
What lead time should I expect?
Quotation and free DFM analysis within 12 hours. Production can start within 24 hours, and parts ship in 3–5 days.
Those numbers assume a released drawing and available material. If the model needs changes, the DFM note comes first.
Do you sign an NDA?
Yes, on request. Uploads are secure and confidential.
If the product is not public yet, get the NDA signed before you send the CAD files.
Which materials do you machine most?
Aluminium 6061, 6061-T6, 7075 and 6082 for housings and brackets. Stainless 303, 304, 316L and 17-4PH for medical and food-contact parts.
Also 4130 and 4140 steel, C36000 brass, copper, Ti-6Al-4V, Inconel, magnesium, and plastics including POM, PEEK, PC and ABS.
Can you handle finishing as well as machining?
Yes. Anodizing, electroless nickel, zinc, silver and gold plating, powder coating, black oxide, bead blasting, tumbling, brushing and polishing.
Laser marking is available down to 1.5 mm character height.
Send a drawing and get a DFM note back
Upload your model and drawing. You get a quotation and free DFM analysis within 12 hours, with the machine class and inspection scope stated in the quote.
12-hour quote±0.005 mm100% inspectionNo MOQ
More machining notes
We publish setup notes, tooling trials and inspection data from the factory floor.
