San Antonio Precision CNC Services: How to Choose a Supplier

• 1
  What matters most when you compare shops
• 2
  Match the part to the right process
• 3
  Tolerance: what ±0.005 mm actually covers
• 4
  Five-axis capacity and when it is the wrong call
• 5
  Lead time: separate quoting, setup, and shipping
• 6
  Order quantity, certifications, and quotingscope
• 7
  Materials and finishes that change the price
• 8
  Inspection and documentation you should require
• 9
  How to run the supplier comparison in six steps

A supplier that quotes ±0.005 mm is stating a process limit, not a promise on every dimension. That number applies to specific features on a specific machine, usually a 5-axis center with a temperature-stable setup. When you read a capacity sheet, look for the phrase 'positional tolerance' next to the number. If the shop writes ±0.005 mm without saying which features, ask for a sample inspection report.

Inch drawings are common in San Antonio. ±0.005 mm equals ±0.0002 in, so a callout of ±0.0005 in is looser and cheaper to hold. Do not tighten a tolerance unless the function needs it. Every extra decimal adds inspection time, and inspection is often the longest step in a short run.

Surface finish travels with tolerance. A bore held to ±0.005 mm usually needs Ra 0.8-1.6 μm or finer. As-machined surfaces sit at Ra 1.6-3.2 μm. If your drawing says Ra 0.4 μm and ±0.005 mm on the same bore, expect a separate finishing operation and a longer quote.

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  Ask which features hold the tight toleranceDatums, bores, and mating faces are typical. Cosmetic surfaces are not.
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  Convert inch callouts before comparing±0.0002 in = ±0.005 mm. Mixing units hides real differences between quotes.
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  Tie finish to functionSealing surfaces and bearing bores need fine finish; clearance holes do not.

Five-axis machining removes setups. On a part with pockets on three faces, a 3-axis shop machines each face in a separate operation, and each re-clamp adds positional error. A simultaneous 5-axis center cuts those faces in one cycle, so the relationship between features stays tight. That is the real benefit, not the machine count.

It is also the wrong choice for some parts. A flat bracket with six holes on one face runs faster and cheaper on a 3-axis mill. A shaft with a cross-hole runs well on a 4-axis mill or a mill-turn center. Requesting 5-axis for simple geometry raises the hourly rate without improving the part.

Size matters too. GreatLight runs 16 simultaneous 5-axis centers with travels from 500 × 310 × 200 mm up to 4,000 × 400 × 150 mm, plus a Ø400 mm rotary table. If your part exceeds the travel envelope on one axis, the shop must reposition it, and that reintroduces the setup error you were trying to avoid.

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  Count the faces with featuresThree or more faces with tight relationships is the practical 5-axis trigger.
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  Check the travel envelope against your partA part that fits on paper can still need repositioning if the fixture eats space.
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  Do not pay for 5-axis on a flat partA 3-axis quote will be lower and the part will be just as good.

Suppliers quote lead time as one number, but it has three parts. Quoting and DFM review come first. Then material purchase and setup. Then machining and inspection. A shop that says '3 to 5 days' is usually describing machining, not the whole chain.

Ask what happens before the spindle starts. At GreatLight, quotation and DFM analysis come back within 12 hours, and production can start within 24 hours once the drawing and material are confirmed. Parts ship in 3-5 days for standard work. The gap between those numbers is where delays live.

Material is the most common delay. Aluminum 6061 and 7075 are stocked in most shops. Inconel, titanium TC4, and 17-4PH may need ordering, which adds days before setup begins. If your schedule is tight, confirm material availability in the RFQ, not after the order.

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  Get the quote turnaround in writing12 hours is a realistic target for a complete drawing set.
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  Ask about material stock before you commitExotic alloys and large plate stock drive the schedule more than machine time.
• 3
  Plan inspection into the timeline100% inspection before shipment is standard; CMM reports take extra time.

Minimum order quantity is the first filter for prototypes. Some shops set an MOQ of 100 pieces because setup cost dominates. GreatLight runs from one prototype to 10,000+ part runs with no minimum order. That matters when you need three parts to test a fit before committing to a production run.

Certifications answer a different question: can this shop serve your industry. ISO 9001:2015 covers general quality management. IATF 16949:2016 is the automotive and EV standard. ISO 13485:2016 applies to medical devices. ISO 27001:2022 covers information security, which matters when you send proprietary CAD files. Match the certificate to your sector before you compare price.

Quoting format tells you how the shop thinks. A one-line price is hard to audit. A quote that lists material, machining time, finishing, inspection, and shipping lets you see where cost sits and where you can relax a tolerance to save money. Ask for that breakdown on the first RFQ.

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  Confirm MOQ before you design the test planNo minimum order lets you validate a prototype without a production commitment.
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  Match certificates to your industryAerospace, medical, and automotive each expect different documentation.
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  Ask for an itemized quoteMaterial, machining, finish, inspection, shipping. One line hides too much.

Material choice moves cost more than most engineers expect. Aluminum 6061 machines fast and holds tolerance well. 7075 is stronger but gummier, so feeds and speeds change and cycle time rises. Stainless 316L work-hardens, which means light passes and more tool wear. Titanium TC4 and Inconel need rigid setups and slow cutting, and both are priced by the pound before machining starts.

Finishing is a second cost center. Anodizing, plating, powder coating, and black oxide all add a vendor step and a queue. Laser marking has a practical floor: minimum character height 1.5 mm. If your part number is smaller than that, the mark will not read cleanly, and you will need a different identification method.

The trap is specifying a finish for appearance when the function does not need it. A clear anodize on a hidden bracket adds cost and lead time for no benefit. Save the cosmetic finish for customer-facing surfaces and leave internal parts as machined.

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  Ask for material-specific cycle timeThe same part in 6061 and 316L can differ by 40% in machining time.
• 2
  Check the finish vendor queueAnodizing and plating are outside processes and add days, not hours.
• 3
  Respect the laser marking minimum1.5 mm character height is the floor for a legible mark.

A certificate proves the shop has a system. An inspection report proves your parts are correct. Ask for the report format before the order. A CMM report with datum callouts, measured values, and pass or fail against the drawing is worth more than a scanned certificate.

GreatLight inspects 100% of parts before shipment, covering raw material check, in-process monitoring, and final inspection, with reports on request. For first articles, ask for a full dimensional report. For production runs, agree on which features get measured every lot and which get sampled.

If your part is safety-related, ask how nonconforming parts are handled. A shop that can describe its quarantine and disposition process is easier to audit than one that only talks about its machines.

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  Request the report, not just the certificateMeasured values against the drawing are the useful document.
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  Agree on first-article scopeFull dimensional report on the first part, then a defined sampling plan.
• 3
  Ask about nonconformance handlingQuarantine and disposition describe the process better than a slogan.