Processing Factory Checks: 7 Steps Before You Order
This guide is for engineers and sourcing staff comparing processing factory quotes. It walks through the checks that decide whether a shop can hold ±0.005 mm, hit a 3–5 day ship window, and keep your drawings confidential. Read it before you send a PO.
In this article
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Key takeaways
What to compare across processing factory quotes
Use the same questions on every shop so the answers line up.
| Check | What good looks like | Red flag |
|---|---|---|
| Tolerance | ±0.005 mm confirmed per feature after DFM | Blanket claim with no feature list |
| Lead time | Quote 12 h, start 24 h, ship 3–5 days | One vague date for everything |
| MOQ | One prototype to 10,000+ parts | Minimum 500 pieces on a first order |
| Certifications | ISO 9001, IATF 16949, ISO 13485, ISO 27001 | Certificate expired or out of scope |
| Quoting basis | Drawing, material, tolerance, finish, qty | Price given without reading the drawing |
| Inspection | 100% before shipment, reports on request | Sample check only, no report |
| Data handling | Secure upload, NDA on request | Email-only drawings, no NDA |
| Size range | Up to 4,000 mm where needed | No stated machine travel |
The short version
Pick the shop that answers five questions in writing: setups, material grade, tolerance per feature, inspection level, and the three lead-time dates. Price comes after that, not before.
Does the processing factory have the right machines for your part?
Machine count alone tells you little. What matters is whether the shop owns the axis count your geometry needs. A bracket with holes on three faces can run on a 3-axis mill with two setups. A hydraulic manifold with ports at compound angles needs a 4-axis or 5-axis machine, or it needs custom fixtures that add cost and error.
Ask for the machine list by travel size. GreatLight runs 127 high-precision CNC machines, including 16 simultaneous 5-axis machining centers, 12 four-axis mills, 27 three-axis machines, and 16 mill-turn centers. Travel ranges cover 500 × 500 × 450 mm up to 4,000 × 400 × 150 mm, with a Ø400 mm rotary table for round work.
If your part is longer than 1,000 mm, the shop needs a machine that can hold it without repositioning. Every reposition adds a datum shift. For long shafts and rails, mill-turn centers remove that risk because turning and milling happen in one setup.
A short note on the axis question: more axes do not automatically mean a better part. They mean fewer setups, tighter position between features, and less fixture cost. That is the trade you are buying.
- 1Single setup winsFewer setups means less stack-up error between features.
- 2Check travel, not tonnageA large machine that cannot reach your part is no help.
- 3Round partsA Ø400 mm rotary table suits flanges and rings.
Tolerance and surface finish: what to put on the drawing
Tolerance is not a shop-wide number. It is a per-feature number. A processing factory that quotes ±0.005 mm for the whole part is either guessing or planning to inspect only the easy features. Put the tight tolerance on the two or three features that actually seal, mate, or locate. Leave the rest at general tolerance.
Finish follows the same logic. As-machined surfaces sit around Ra 1.6–3.2 μm, which is fine for brackets and housings. Sealing faces and bearing bores usually need Ra 0.8–1.6 μm. Optical and sliding contact surfaces may need Ra 0.2–0.8 μm, which often means a finishing pass or a secondary operation.
Material choice changes what is realistic. Aluminium 6061 and 7075 cut cleanly and hold tight tolerance well. Stainless 316L and 17-4PH work harden, so light passes and sharp tools matter. Titanium TC4 and Inconel move more under heat, so the shop needs to manage coolant and cutting speed, not just the program.
Before you commit, ask for a DFM review. A good shop will flag a 0.2 mm wall, a deep narrow slot, or a tolerance that needs a grinder rather than a mill. GreatLight returns a quotation and free DFM analysis within 12 hours.
- 1Tight where it countsReserve ±0.005 mm for sealing and locating features.
- 2Finish by functionRa 1.6–3.2 μm as-machined, Ra 0.8–1.6 μm for sealing faces.
- 3Hard materials moveTitanium and Inconel need slower speeds and heat control.
Lead time, MOQ, and how the quote is built
Lead time claims are easy to make and hard to check. Split the number into three parts before you compare shops: how fast they quote, how fast they start, and how fast parts ship. GreatLight quotes within 12 hours, can start production within 24 hours, and ships parts in 3–5 days. Those are three separate commitments, and each one can slip for different reasons.
MOQ is the second filter. If you are in the design phase, a shop with a 500-piece minimum will not help you iterate. A workable range is one prototype up to 10,000+ parts, so the same supplier follows the part from first article to production. Switching shops between prototype and production forces a new DFM cycle and a new first-article inspection.
Read the quote line by line. A price built from a drawing, a material grade, a tolerance callout, a finish spec, and a quantity is a real price. A price given before anyone opened the drawing is a placeholder. Ask what is included: material certification, inspection report, surface finish, and packaging.
Volume pricing should be a curve, not a cliff. If the price drops 40% between 10 and 100 pieces, ask why. Sometimes it is setup amortization. Sometimes the shop plans to move your part to a different machine. Both are fine, as long as you know which one.
- 1Three clocksQuote, production start, and ship date are separate numbers.
- 2Prototype to volumeOne supplier from 1 piece to 10,000+ keeps the process stable.
- 3Ask what is includedReports, certification, and finish should be named in the quote.
Certifications, inspection, and confidentiality
Certification scope matters more than the certificate count. ISO 9001:2015 covers general quality management. IATF 16949:2016 is what automotive and EV programs look for. ISO 13485:2016 applies to medical devices. ISO 27001:2022 covers information security, which is the one that answers questions about your drawings. Check the scope statement, not just the logo.
Inspection is where tolerance claims become real. Ask what happens between raw material and shipping. A sound process checks incoming material, monitors dimensions during the run, and inspects the final part. GreatLight inspects 100% before shipment and provides reports on request. If a shop only checks a sample, ask how they catch a drift that starts at piece 40.
Confidentiality is a normal requirement, not a special favor. Your drawings carry your design intent. Secure upload and an NDA on request should be standard. If a shop pushes back on a mutual NDA for a production program, treat that as a signal about how they handle files in general.
One practical tip: send a marked-up drawing with the critical features highlighted. It takes ten minutes and it removes most of the back-and-forth about what matters and what does not.
- 1Read the scopeA certificate outside its scope does not cover your process.
- 2100% inspectionFinal inspection of every part, reports available on request.
- 3NDA on requestSecure upload and a mutual NDA are routine, not extra.
Materials, finishes, and the post-machining step
A processing factory that only machines metal leaves you to find an anodizer, a plater, and a laser marker on your own. Each handoff adds a week and a new place for parts to be damaged. Ask upfront which finishes are done in-house or with a controlled partner.
Common material groups cover most programs: aluminium 6061, 6061-T6, 2024, 5052, 5083, 6063, 6082, 7075, and ADC12; stainless 303, 304, 316, 316L, 420, 430, 431, 440C, and 17-4PH; steel 1018, 1045, 4130, 4140, 4340, A36, and tool steel; copper and brass C101, C103, C110, C27400, C28000, and C36000; titanium TA1, TA2, TC4, plus Inconel and magnesium AZ31B or AZ91D. Plastics run from ABS and PC to POM, PEEK, and carbon fibre.
Finishes change dimensions, and this catches people out. Anodizing adds a few micrometres per surface. Hardcoat anodizing adds more and can shift a tight bore. Electroless nickel, zinc, silver, and gold plating each build thickness. If a plated bore has a ±0.01 mm tolerance, the shop must machine it undersized on purpose.
Laser marking has a floor too. Minimum character height is about 1.5 mm for a clean, readable mark. If your part number needs to fit in a 2 mm space, plan a different marking method early, not after the parts are finished.
- 1Fewer handoffsIn-house or controlled finishing keeps the schedule and the finish consistent.
- 2Plating moves dimensionsMachine undersized when a coated bore is tolerance-critical.
- 3Marking limitMinimum character height around 1.5 mm for laser marking.
Where a low-cost quote usually goes wrong
The cheapest quote is often correct for simple parts. It goes wrong in predictable places. The first is setup count: a shop quotes three setups when the part needs six, then asks for a change order. The second is material: a lower grade is substituted because the quote never named the grade. The third is finishing, quoted as a separate line that arrives later.
The fourth is inspection. If the quote assumes sampling and your drawing needs 100% inspection, the gap shows up as a schedule slip or a rejected lot. The fifth is packaging. Bare parts in a bag arrive with nicks on a polished face, and now you own a rework cycle that nobody priced.
None of these are dishonest by default. They are the result of a quote built from an RFQ email instead of a reviewed drawing. The fix is simple: ask for the assumptions in writing. Setup count, material grade, finish spec, inspection level, and packaging. Five lines on a quote prevents most disputes.
A shop that answers those five questions quickly is usually a shop that will also answer your emails during the run. That is worth more than a few percent on the piece price.
- 1Setup countAsk how many setups the quoted price assumes.
- 2Named materialGrade and temper should appear on the quote.
- 3PackagingFinished surfaces need protection priced into the job.
Industries and the extra requirements they add
The same machine can serve several industries, but the paperwork changes. Aerospace work leans on material traceability and first-article inspection. Automotive and EV programs expect IATF 16949 discipline and often PPAP-style documentation. Medical devices bring ISO 13485 and a stricter change-control trail.
Robotics and automation parts sit between prototype and production. You may need five units this month and two hundred next quarter, with no design freeze in between. A processing factory that handles that range without re-quoting from scratch each time saves real engineering hours.
Electronics and new energy work often involves heat management. Aluminium heatsinks, copper busbars, and thin housings need flatness control, because a warped base defeats a thermal interface. That is a fixturing and stress-relief problem more than a tolerance problem.
Industrial machinery parts are usually large and low volume. Here the constraint is machine travel and crane capacity, not cycle time. Check that the shop can move and hold a 1,500 mm casting before you send the drawing.
- 1AerospaceTraceability and first-article inspection drive the cost.
- 2Automotive and EVIATF 16949 documentation is expected, not optional.
- 3MedicalISO 13485 and a documented change-control trail.
7 steps to qualify a processing factory
Run these in order. Each step can remove a shop before you spend engineering time on it.
- 11. Send a controlled drawingUse a PDF with revision, material grade, tolerance callouts, finish spec, and quantity. Note which features are critical. Skip this and every quote you receive is an estimate, not a price.
- 22. Request a DFM review with the quoteAsk for comments on thin walls, deep slots, and tolerance stack-up. A usable shop returns both within 12 hours and names the features it cannot hold.
- 33. Confirm the machine and setup countAsk which machine will run the part and how many setups the price assumes. Compare that against your geometry. A 5-axis part quoted at two setups is a warning.
- 44. Fix the tolerance and finish per featureKeep ±0.005 mm on sealing and locating features only. Set Ra 0.8–1.6 μm for sealing faces and Ra 1.6–3.2 μm elsewhere. This single step often cuts cost more than shopping around.
- 55. Nail down the three datesGet the quote date, production start date, and ship date in writing. For reference, GreatLight quotes in 12 hours, starts within 24 hours, and ships in 3–5 days.
- 66. Agree on inspection and paperworkState the inspection level, whether reports are needed, and which certifications apply. If the part is medical or automotive, confirm the scope before the first chip is cut.
- 77. Place a small first orderRun 1 to 10 pieces and measure them yourself. No MOQ means you can do this. A shop that holds tolerance on the first article is a shop worth scaling with.
Common questions
What tolerance can a processing factory actually hold?
±0.005 mm is realistic on rigid features in aluminium and stainless when the shop confirms it after a DFM review. It is not realistic on a thin unsupported wall or a deep narrow slot, because tool deflection and heat move the cut.
Put the tight callout only where the function needs it, and let the rest sit at general tolerance. That keeps the price sane and the inspection focus clear.
Is a low MOQ a sign of a small shop?
Not necessarily. No minimum order quantity usually means the shop is set up for prototype work, with quick changeover and flexible fixturing. That capability is separate from production capacity.
GreatLight runs one prototype up to 10,000+ part runs. The same process and inspection applies at both ends, which is what keeps a design stable from first article to volume.
How do I compare quotes that use different formats?
Normalize them yourself. Build a table with five rows: setup count, material grade, tolerance per critical feature, finish spec, and inspection level. Ask each shop to fill it in.
Once the five rows match, the remaining difference is real price, not a packaging difference in how the quote was written.
Do I need an NDA before sending drawings?
If the part is proprietary, yes. A mutual NDA is routine and should not slow anything down. Secure upload matters just as much, because it covers the file in transit and at rest.
Ask how long drawings are retained after the job and who can open them. A shop with ISO 27001:2022 in scope will have a written answer.
What causes a first article to fail?
Three common causes: an unclear datum on the drawing, a finish that was applied after final inspection, and a tolerance that the process cannot hold without a secondary operation.
All three are visible before cutting metal if the shop reviews the drawing properly. That is why the DFM step matters more than the quoted price.
Can one factory cover prototype and production?
Yes, if the machine range and inspection process are the same for both. That is the practical argument for a supplier with no MOQ and a wide machine list.
Watch for shops that prototype on one machine and produce on another without telling you. Ask which machine will run the production order.
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Upload your files and we return a quotation with free DFM analysis within 12 hours. No minimum order quantity, 100% inspection before shipment, NDA on request.
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