Buyer guide

Aluminum processor selection CNC machining: 7 checks before you commit

This guide is for engineers and sourcing teams who buy machined aluminum parts and need a repeatable way to compare suppliers. It covers alloy, tolerance, inspection, lead time and MOQ so you can rank quotes instead of guessing.

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±0.005 mm toleranceNo MOQISO 9001 / IATF 16949Quote in 12 hours

Aluminum processor selection CNC machining on a 5-axis cell

On this page

1
What matters most
2
Seven checks mapped to the part you are buying
3
Start with the alloy, not the hourly rate
4
Tolerance, thin walls and the geometry that decides the process
5
Surface finish and how the supplier proves it
6
Lead time, MOQ and the commercial terms that matter
7
Certifications, confidentiality and the questions to ask early
8
Seven steps to a comparable quote

Key takeaways

What matters most

Alloy first, price second6061-T6, 6082 and 7075 behave differently; confirm the temper on the drawing.

Ask for the tolerance stackA ±0.005 mm callout on one bore is not the same as a ±0.005 mm process window.

Thin walls decide the supplierAnything under 1.0 mm wall thickness needs fixture planning, not a lower feed rate.

Quote speed tells you about capacityA DFM reply in 12 hours usually means the shop has spare spindle time.

Certificates must match your industryIATF 16949 for automotive, ISO 13485 for medical, ISO 27001 for data handling.

Selection matrix

Seven checks mapped to the part you are buying

Use the left column as your RFQ checklist.

Check	Ask for	Pass condition
Alloy and temper	Mill certificate	6061-T6 or 6082-T6 matches the print
Tolerance	Process capability note	±0.005 mm on critical features
Wall thickness	Fixture and tool plan	Stable under 1.0 mm walls
Surface finish	Sample or Ra reading	Ra 0.8–1.6 μm as machined
Inspection	First article report	Dimensional report before shipment
Lead time	Firm start date	Production starts within 24 hours
MOQ	Order ladder	One prototype to 10,000+ parts

Pick the processor that answers the drawing, not just the price

If the alloy, tolerance, finish and inspection plan all come back in writing within a day, you have a supplier worth a trial order. If any of the four is missing, the quote is not comparable yet.

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Alloy and stock

Start with the alloy, not the hourly rate

Most aluminum RFQs fail at the material line. A print that says "aluminum 6061" leaves the temper open, and 6061-O machines very differently from 6061-T6. Hardness changes chip formation, tool wear and the final surface. If the drawing does not state temper, write it into the RFQ before you compare prices, because two shops quoting different stock are not quoting the same part.

GreatLight runs 6061, 6061-T6, 2024, 5052, 5083, 6063, 6082, 7075 and ADC12. That range covers most brackets, housings, heat sinks and structural plates. For a part that sees load, 7075 gives higher strength but machines slower and costs more per kilogram. For an enclosure, 5052 or 6063 is usually enough and anodizes cleanly.

Ask how the supplier stores and identifies stock. Mixed bar stock is a real risk on multi-part orders. A shop that keeps alloy and heat lot traceable can answer a material question months later. One that cannot will ask you to accept a substitution you did not approve.

1
State the temper6061-T6 is not interchangeable with 6061-O on a stressed part.
2
Check the mill certificateIt confirms alloy and heat lot, not just the grade name.
3
Flag recycled stockSecondary alloy can change machinability between lots.

Tolerance and geometry

Tolerance, thin walls and the geometry that decides the process

A ±0.005 mm tolerance is a process window, not a magic number. It holds on a 5-axis machining center when the setup is rigid, the tool is short and the material is stable. It gets harder on a tall thin rib, a deep pocket or a part that needs three re-clampings. Ask which features carry the tight callout and whether the supplier plans to hold it in one setup or across several.

Simultaneous 5-axis work reduces setups, which reduces stack-up error. GreatLight runs 16 simultaneous 5-axis machining centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers. Maximum processing size is 4,000 mm, and the largest travel is 4,000 × 400 × 150 mm. Parts that fit a single setup are cheaper and more repeatable than parts that need five.

Thin walls are the usual failure point. Below 1.0 mm, cutting force pushes the wall away from the tool, so the finished thickness varies along the length. The fix is fixture support and light finishing passes, not a slower spindle. If your design has a 0.8 mm wall next to a thick boss, expect a conversation about draft, support or a change in the wall.

1
One setup beats fiveEvery re-clamp adds positional error to the stack.
2
Deep pockets need reachLong tools deflect; plan a shorter cutter or EDM.
3
Round the inside cornerA corner radius larger than the cutter diameter saves time.

Finish and inspection

Surface finish and how the supplier proves it

Finish callouts get ignored more often than tolerance callouts. Ra 1.6–3.2 μm is normal as-machined output. Ra 0.8–1.6 μm needs a controlled finishing pass and a sharp cutter. Ra 0.2–0.8 μm usually means a secondary operation such as lapping or polishing, and it belongs on the drawing as a separate line item.

Anodizing changes dimensions. Clear anodizing adds a thin oxide layer and can shift a tight bore by a few micrometres. Hardcoat adds more. If a bore is anodized after machining, tell the supplier whether the callout applies before or after coating, and let them compensate. Color anodizing also varies by lot, so a cosmetic part should be approved from a physical sample.

Inspection is where quotes separate. GreatLight inspects 100% of parts before shipment and runs raw material checks, in-process monitoring and final inspection, with reports on request. A supplier that offers only a packing slip is asking you to carry the risk. Ask for the first article report and the sampling plan in writing before the order starts.

1
Split the finish calloutMachined Ra and polished Ra are different operations.
2
Compensate for coatingAnodizing adds material to every external surface.
3
Agree on the reportName the features you want measured and the format.

Lead time and MOQ

Lead time, MOQ and the commercial terms that matter

Lead time is a capacity signal. A shop that can start production within 24 hours has open spindle time; one that quotes six weeks is booked or slow. GreatLight returns a quotation and free DFM analysis within 12 hours and ships parts in 3–5 days on standard aluminum work. Historical late-delivery probability is below 2%, which is a useful number to compare against a verbal promise.

MOQ is the other gate. Some processors will not quote below 100 pieces, which pushes prototyping into a different channel and breaks the link between the prototype and the production part. GreatLight has no minimum order quantity and runs from one prototype to 10,000+ part runs on the same equipment, so the process you validate is the process you scale.

Put the commercial terms in the RFQ, not in a follow-up email. Ask for the alloy source, the inspection plan, the finish sequence, the packaging method and the shipping terms. A quote that answers all five is comparable. One that answers price only will cost you time later, and usually more money.

1
Quote in 12 hoursFree DFM analysis comes back with the price.
2
No minimum order quantityOne piece and 10,000 pieces use the same machines.
3
Ask for the planInspection, finish and packaging belong in the quote.

Certification and risk

Certifications, confidentiality and the questions to ask early

Certification is a filter, not a score. ISO 9001:2015 covers the quality system. IATF 16949:2016 is what automotive and EV buyers look for. ISO 13485:2016 applies to medical device work. ISO 27001:2022 covers information security, which matters when you send CAD files across borders. Match the certificate to your industry and ask for the scope, not just the logo.

Confidentiality should be settled before drawings move. Uploads are secure and confidential, and a non-disclosure agreement is available on request. For a new supplier, sign the NDA first, then release the drawing. It costs one email and removes the argument about what was shared if the program changes hands.

Ask about sub-tier suppliers. Anodizing, plating and heat treatment are often outsourced, and each step adds a handoff where a part can be mixed up or delayed. A supplier that controls post-processing or names its sub-tier partners gives you a shorter, more predictable chain. That is the difference between a shop and a supply chain.

1
Match the certificateIATF for automotive, ISO 13485 for medical.
2
Sign the NDA firstThen release drawings and models.
3
Map the sub-tiersEvery outsourced step is another handoff.

RFQ checklist

Seven steps to a comparable quote

Run these in order. Each step removes one source of mismatch between suppliers.

1
Lock the alloy and temperWrite the grade and temper on the drawing, for example 6061-T6 or 6082-T6. Add the mill certificate requirement to the RFQ so every shop quotes the same stock.
2
Mark the critical featuresFlag the two or three features that carry the tight callout instead of putting ±0.005 mm on the title block. State whether the tolerance applies before or after anodizing.
3
Send the finish sequenceList machining, deburring, anodizing, laser marking and packaging in order. Name the Ra value for each surface and the minimum character height for marking, typically 1.5 mm.
4
Ask for the inspection planRequest a first article report, the sampling plan for the run and a dimensional report before shipment. 100% inspection is the baseline; the report format is the detail.
5
Test the DFM responseSend the model and see what comes back. A useful reply names specific features: a deep pocket, a thin wall, a corner radius smaller than the cutter. A generic reply is a warning.
6
Confirm capacity and lead timeAsk for the machine type, the number of setups and the production start date. Compare the answer against the ship date, not against the price.
7
Settle commercial termsConfirm MOQ, packaging, shipping terms and the NDA. Then place a small first order and inspect it against the report before releasing the full volume.

FAQs

Questions buyers ask before the first order

What tolerance can an aluminum CNC processor actually hold?

On rigid, single-setup features, ±0.005 mm is realistic on a modern machining center. The limit is usually the part, not the machine: long thin walls, deep pockets and multi-setup work all widen the practical window.

Send the drawing with the critical features marked and ask which ones the supplier will hold in one setup. That answer tells you more than a general tolerance claim.

Is a lower price worth a longer lead time?

Only if the schedule has slack. A cheap quote with a six-week window often means the work is queued behind higher-priority jobs, and a slip moves the whole build.

Compare the production start date, not just the ship date. A shop that starts within 24 hours can absorb a revision; one that starts in three weeks usually cannot.

How do I compare quotes from different processors fairly?

Give every supplier the same package: alloy and temper, critical features, finish sequence, inspection plan and packaging. Then compare line by line.

A quote that answers all five items is comparable. If one supplier omits the inspection plan or the finish sequence, ask for it before you rank the price.

Do I need an NDA before sending CAD files?

For a new supplier, yes. It is a short document and it settles ownership of the design before the program starts. GreatLight offers a non-disclosure agreement on request and treats all uploads as confidential.

Sign it, then release the model. Keeping the NDA and the drawing in the same email thread makes the timeline clear if anything is disputed later.

Can one supplier handle both prototyping and production?

Yes, and it is usually better. Running the prototype and the production batch on the same equipment and the same inspection process removes the transfer step where tolerances drift.

GreatLight has no minimum order quantity and machines runs from one prototype to 10,000+ parts. The trade-off is that a very small shop may be cheaper on a single piece but cannot scale when volume arrives.

Which certifications should an aluminum processor hold?

ISO 9001:2015 is the baseline for a documented quality system. Add IATF 16949:2016 for automotive and EV work, ISO 13485:2016 for medical devices, and ISO 27001:2022 when data security is part of the contract.

Ask for the certificate scope, not just the certificate. A valid document that excludes your process tells you nothing about the parts you are buying.