Why Subcontract CNC Processing? 5 Shop Problems It Fixes

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  Five Symptoms That Point to Subcontract CNC Processing
• 2
  Machine Hours Are the Bottleneck, Not Skill
• 3
  Tolerance Creep on Older or Worn Machines
• 4
  Setup Count Is Eating Your Margin
• 5
  Low Volume Does Not Pay for Tooling or Fixtures
• 6
  Finishing and Certification Steps You Cannot Do In-House
• 7
  When Subcontract CNC Processing Is the Wrong Move
• 8
  How to Hand Off a Job Without Losing a Week

Most shops that ask about subcontract CNC processing are not short on talent. They are short on spindle hours. A job shop with 20 machines and 35 open work orders will always lose the arithmetic battle somewhere, and the losing job is usually the one with the longest cycle time, not the highest margin.

The first check is simple. Pull the last four weeks of machine logs and add up scheduled hours against quoted hours. If the ratio sits above 0.9, you are already running late on paper. No amount of overtime fixes that for more than a month, because setup time does not shrink when the shift gets longer.

Outsourcing the overflow works because it moves whole operations, not individual parts. Send the roughing of a batch to a subcontractor and keep the finishing in-house, or send one part family out completely. Both reduce hours. The second option is cleaner because it removes setup, programming and inspection from your queue at the same time.

One caution. Overflow work still needs its own fixture, its own first-article report and its own shipping step. If the lot is under 20 pieces and the geometry is simple, the paperwork may cost more time than the machining saves.

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  Rule of thumbAbove 90% scheduled load, price the overflow outside.
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  Keep in-houseParts with proprietary fixturing or tight process know-how.
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  Send outLong-cycle roughing, simple turned parts, one-off brackets.

Tolerance creep is slow and easy to miss. A machine that held ±0.01 mm last year now needs a warm-up cycle before it repeats. Operators compensate with offsets and the parts still pass, until a batch of 200 does not.

The usual causes are not dramatic. Ball screw wear, spindle growth after two hours of cutting, coolant temperature swings, or a fixture that has been re-clamped too many times. On aluminium, thermal growth alone can move a bore 0.008 mm between the first and last part of a run.

Subcontract CNC processing helps here because a shop that runs 5-axis work daily holds tighter process control than a general shop does by accident. GreatLight machines to ±0.005 mm (±0.0002 in) and inspects 100% of parts before shipment, with raw material checks, in-process monitoring and final inspection reports on request.

Do not send a creeping process out without data. Write down which dimension drifts, by how much and after how many parts. A subcontractor who receives that note will quote the right process. One who does not will guess, and you will pay for the guess twice.

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  Measure firstLog drift across a full run, not a single part.
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  Report the rangeState the tolerance band you actually need, not the drawing limit.
• 3
  Ask for capabilityRequest Cp/Cpk data on the critical feature if volume justifies it.

Every extra setup adds two costs: the time to fixture the part, and the error that comes from re-datuming. A bracket that needs four faces machined on a 3-axis mill may take five setups. Each one adds 20 to 45 minutes and a fresh chance to be 0.02 mm off.

This is the clearest case for subcontract CNC processing. A shop with simultaneous 5-axis capacity machines those faces in one or two setups, because the rotary table presents the part to the cutter instead of the operator re-clamping it. GreatLight runs 16 simultaneous 5-axis machining centers alongside 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers.

The decision line is around three setups. Under three, keep it in-house if your machines are free. Over three, get a quote. The savings are not only hours; they are scrap risk, and scrap on a near-finished part is the most expensive kind.

Watch the workpiece size. Five-axis work has travel limits. GreatLight covers up to 4,000 mm maximum processing size, with common envelopes of 750 × 1,150 × 550 mm, 600 × 600 × 600 mm and compact 500 × 500 × 450 mm. If your part is bigger than the envelope, the setup count may not be the real constraint.

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  Count setupsIf it exceeds three, price it out.
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  Check travelConfirm the part fits the subcontractor's envelope before quoting.
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  Send the modelSTEP with GD&T gives a faster and more accurate DFM response.

A 40-piece run rarely justifies a dedicated fixture. Engineers still design one, because the alternative is a vise and a dial indicator. Then the job ships and the fixture sits on a shelf for two years.

The arithmetic favors subcontract CNC processing when the fixture cost divided by the lot size is larger than the part margin. That happens often below 100 pieces, and almost always below 20. A subcontractor who already owns a modular fixturing system spreads that cost across many customers.

There is a second effect. Small lots from many customers often share tooling families: similar pocket depths, similar thread sizes, similar materials. Grouping work lets a subcontractor run the parts back to back and cut the non-cutting time. Your one-off job rides along with that efficiency.

Volume thresholds are not fixed. GreatLight runs from one prototype to 10,000+ part runs with no minimum order quantity, so the crossover point is decided per part, not by a floor price. Ask for both scenarios: 50 pieces and 500 pieces. The gap tells you how much tooling is hidden in the unit price.

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  Do the mathFixture cost ÷ lot size vs. part margin.
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  Ask for two quotesLow volume and high volume, side by side.
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  ReuseIf a subcontractor already holds similar tooling, say so in the RFQ.

A part that meets tolerance can still fail because of finish or documentation. Anodizing, hardcoat, electroless nickel, bead blasting and laser marking all add steps, and each one has its own process window that can move dimensions. Hardcoat anodizing, for example, builds a layer that changes a bore by several micrometres.

The same applies to paperwork. Aerospace, automotive and medical buyers ask for material certificates, inspection reports and traceability. A shop without those routines has to build them per job, and that is slow and error-prone.

This is where a subcontractor with existing certifications removes real work. GreatLight holds ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022, and covers anodizing, plating, powder coating, black oxide, blasting, tumbling, brushing, polishing and laser marking with a minimum character height of 1.5 mm.

Confidentiality matters as much as capability at this stage. Drawings for an unreleased product should not travel by email attachment. Uploads are handled as secure and confidential, and an NDA is available on request before any file changes hands.

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  Finish changes sizeCall out coated surfaces on the drawing before quoting.
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  Match certificationsMedical and automotive work needs ISO 13485 or IATF 16949.
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  Protect the designRequest an NDA before sending production files.

Outsourcing is not always cheaper, and pretending otherwise wastes everyone's time. Three situations usually argue for keeping work in-house. The first is a process your team is still learning. If you cannot write a clear RFQ for it, you cannot judge the quotes that come back.

The second is a part with a proprietary geometry or coating that defines your product. Sending it out means teaching a supplier your process. Sometimes that is fine, sometimes it is not, and that call belongs to the product owner, not the purchasing team.

The third is a tight feedback loop. Prototype iterations that run on a two-hour cycle in your own shop will slow to days when they cross a supply chain. If you are still changing the design daily, keep the loop short until the geometry stabilizes.

After it stabilizes, the calculation changes. GreatLight starts production within 24 hours of a confirmed order at a quoted lead time of 3–5 days, with historical late-delivery probability below 2%. That is fast for a subcontractor, and still slower than a machine ten metres from your desk.

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  Keep in-houseUnstable designs, proprietary coatings, learning curves.
• 2
  Send outStable geometry, known process, capacity pressure.
• 3
  Split the batchRun the first article in-house, the rest outside.