CNC Machining Services San Francisco: How to Choose

• 1
  Seven checks before you send a PO
• 2
  Which CNC machining route fits your part
• 3
  What CNC machining services San Francisco shops must show on tolerance
• 4
  Lead time, quote speed and what they reveal
• 5
  MOQ, materials and the prototype-to-production gap
• 6
  Certifications, inspection and data handling
• 7
  Machine capacity and part size limits
• 8
  Pitfalls that show up after the PO
• 9
  How to vet a supplier in seven steps

Every supplier claims precision. The useful question is where the number comes from. A general shop holds ±0.05 mm on a good day. Tight work needs a machine that can reach the feature in one setup, because each re-fixture adds stack-up error.

GreatLight holds ±0.005 mm (±0.0002 in) on qualified features. That number depends on simultaneous 5-axis capacity, 16 machining centers in the fleet, and a Ø400 mm rotary table for parts that need angular indexing. It is not a blanket claim across every surface of every part.

Ask which features carry the tight tolerance and which are general. A drawing that calls ±0.005 mm on a cosmetic face is wasting your money. A drawing that calls it on a bearing bore is a real requirement, and the shop should tell you how it will measure that bore.

Surface finish runs on the same logic. Ra 0.2–0.8 μm is a fine finish that usually needs a separate finishing pass or a ground operation. Ra 0.8–1.6 μm is the normal machined-and-fine range. Ra 1.6–3.2 μm is as-machined and costs the least.

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  Name the tight featuresMark them on the drawing so the shop can plan setup and inspection.
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  Match finish to functionSealing faces and sliding surfaces need fine Ra; covers and brackets do not.
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  Ask for the measurement methodCMM, micrometer or gauge pin. The method should fit the tolerance.

A quote that takes a week usually means your file sat in a queue. GreatLight returns a quotation and a free DFM analysis within 12 hours, and production can start within 24 hours of approval. Standard parts ship in 3–5 days.

Those windows only hold when the drawing is complete. Missing tolerances, unclear material callouts and undefined finishes all restart the clock. The fastest shops are the ones that flag these gaps on the first pass instead of machining to a guess.

Late delivery is the cost nobody budgets for. Historical late-delivery probability at GreatLight sits below 2%. Treat any supplier claim above that as a reason to ask for their on-time record, not a promise.

For San Francisco buyers, the practical variable is freight and customs, not machine time. Build the transit leg into your schedule and keep the machining window for the work itself.

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  Send a complete drawingTolerances, material, finish and quantity. Gaps cost days.
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  Ask for the DFM noteIt shows whether the shop read the model or just priced the file size.
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  Separate machine time from transitA 3–5 day build plus freight is not a 3–5 day door-to-door promise.

Minimum order quantity is where a lot of first articles die. GreatLight runs no minimum order quantity, from one prototype to 10,000+ part runs. That matters when you are still proving a design and cannot commit to a batch.

Material range decides whether a shop can even quote you. Aluminum covers 6061, 6061-T6, 2024, 5052, 5083, 6063, 6082, 7075 and ADC12. Stainless covers 303, 304, 316, 316L, 420, 430, 431, 440C and 17-4PH. Steel, copper, brass, titanium and engineering plastics round out the list.

Titanium and Inconel are the materials that expose weak shops. Both hold heat at the cutting edge, so they need lower surface speed and rigid tooling. A supplier that quotes them at aluminum parameters will scrap the part or burn the tool.

Prototype work often mixes processes. A machined housing with a 3D printed cover and a sheet metal bracket is normal. Check whether the shop can carry all three or whether you will manage three vendors and three tolerance stacks.

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  Confirm the exact alloy6061 and 7075 machine differently and price differently.
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  Ask about heat-treat conditionT6 and annealed stock behave differently on thin walls.
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  Keep one vendor where possibleFewer handoffs means fewer tolerance stack-ups to chase.

Certifications are a filter, not a sales badge. ISO 9001:2015 covers general quality systems. IATF 16949:2016 applies to automotive and EV work. ISO 13485:2016 is the medical device standard. ISO 27001:2022 covers information security.

GreatLight holds all four. If your program touches automotive, medical or defense-adjacent work, a supplier without the matching certificate is a compliance risk regardless of price.

Inspection is the other half. GreatLight inspects 100% of parts before shipment, with raw material checks, in-process monitoring and final inspection. Reports are available on request. Ask for them at quote stage so the expectation is set early.

Data handling matters when your models are the product. Uploads are secure and confidential, and an NDA is available on request. Get the NDA signed before you send STEP files, not after.

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  Match certificate to industryISO 9001 is the floor; the others are the gate.
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  Request inspection reports up frontBetter to agree on the report format than argue later.
• 3
  Sign the NDA firstBefore CAD transfer, not after.

Size limits decide feasibility before price matters. GreatLight handles parts up to 4,000 mm, with a large travel of 4,000 × 400 × 150 mm. Medium machines run 750 × 1,150 × 550 mm and 600 × 600 × 600 mm. Compact machines cover 500 × 500 × 450 mm and 500 × 310 × 200 mm.

A 127-machine fleet matters for scheduling, not for bragging. It spreads risk. If one spindle is down, your job does not wait for a repair. The mix includes 16 simultaneous 5-axis centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers.

Mill-turn is the underrated capability. A shaft with milled flats, cross-holes and a threaded end can finish in one chucking instead of three. That removes concentricity error and a day of handling.

Ask for the machine that will run your part, not the best machine in the building. The quote should name the process route.

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  Check the travel envelopeYour part plus fixture must fit, not just the part.
• 2
  Ask which machine is quotedA 5-axis quote on 3-axis work is a pricing red flag.
• 3
  Consider mill-turn for shaftsOne setup, better concentricity, less handling.

The most common failure is a quote built on assumptions. The shop prices 6061 because that is the default, then discovers the drawing says 7075. The price moves and the schedule slips. A good quote lists the alloy, temper, finish and quantity explicitly.

The second is finish mismatch. Anodizing a part that needs a conductive surface, or bead blasting a sealing face, both create rework. Specify the finish per surface, not per part.

The third is inspection scope. A supplier that only measures the features they can reach with calipers will pass a part that fails on a CMM. Agree the measurement plan before the first chip.

Laser marking is a small one with a hard limit: minimum character height is 1.5 mm. If your part number needs to fit in a 1 mm space, plan a different marking method.

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  Get the alloy in writingGrade and temper on the quote line.
• 2
  Specify finish per surfaceMasking and conductive areas need their own callout.
• 3
  Agree the measurement planWhich features, which instrument, which report.