Montana CNC Processing Service: 7 Checks Before You Order

• 1
  Key takeaways
• 2
  Which process fits your part
• 3
  What a strong quote includes
• 4
  Start with tolerance, not with price
• 5
  Match axis count to geometry
• 6
  Material and surface finish change the quote
• 7
  Certifications and inspection paperwork
• 8
  Lead time, MOQ and how the clock runs
• 9
  How to run a first order

A Montana CNC processing service quote means nothing until the tolerance is agreed. Send the drawing with the critical dimensions marked, not the whole print. A typical shop holds ±0.005 mm (±0.0002 in) on ground or bored features, but that number only applies where the geometry allows it. A 300 mm cantilever in aluminum will not hold that on a milling machine, no matter how good the machine is.

Split your tolerances into three groups: critical fits, general dimensions and cosmetic surfaces. Most parts have five to ten dimensions that matter. The rest can sit at ±0.1 mm and cost far less. When you send everything as a tight tolerance, the shop prices the whole part as difficult. The quote comes back high, and nobody knows which feature caused it.

Tolerance also sets the inspection cost. A ±0.05 mm part can be checked with calipers and a height gauge. A ±0.005 mm bore needs a CMM, a pin gauge set or an air gauge, and that time lands in the price. If you only need two bores checked, say so. It keeps the inspection report short and the part affordable.

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  Mark critical dimsFive to ten features, not the full print.
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  Check the datumA datum on a rough cast face will move between setups.
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  Ask what holds ±0.005 mmBores, ground faces and mill-turn work, not long slender walls.

Three-axis machines cut from the top. Four-axis adds a rotary table so the part can be indexed to its side without a refixture. Five-axis moves the tool and the part at the same time, which lets a ball nose cutter reach undercuts and blend a continuous surface in one setup. The difference shows up in the tolerance stack, not just in the cycle time.

Each refixture adds a datum shift. On a part with six faces and a 0.02 mm positional requirement, three setups can eat most of your budget before the first cut. A 5-axis center takes that part in one clamp. It also shortens the process, because the shop no longer has to build three fixtures and prove them out.

Size matters too. Large travel on a 5-axis center reaches 4,000 × 400 × 150 mm. Medium platforms cover 750 × 1,150 × 550 mm and 600 × 600 × 600 mm. Compact ones handle 500 × 500 × 450 mm and 500 × 310 × 200 mm. Send the bounding box with the drawing so the shop picks the right platform instead of guessing. A Ø400 mm rotary table sets the practical limit for round parts that need indexing.

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  One setup, fewer datumsThe main reason to pay for 5-axis on a tight part.
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  Watch the envelopeA part that fits on paper may not clear the fixture.
• 3
  Long slender partsSupport them or the finishing pass will sing.

Aluminum 6061 and 6061-T6 are the default for prototypes and brackets. They cut fast and hold a good finish. Switch to 7075 and the same part takes longer, because the tool load goes up and the chips break differently. Stainless 303 and 304 are common, but 316L and 17-4PH (SUS630) work-harden and need slower feeds and sharper tools. Titanium Ti-6Al-4V is a different order of cost again.

Plastic parts follow the same logic. POM and ABS machine cleanly. PEEK and carbon fiber reinforced grades wear tools and can delaminate if the cutter pushes too hard. If your part is a cover or a housing and the load is low, a cheaper grade with the same stiffness may pass. Say what the part does, not just what it is made of.

Finish is the second half of the quote. As-machined surfaces sit around Ra 1.6–3.2 μm. A high-quality machined finish reaches Ra 0.8–1.6 μm, and fine work goes to Ra 0.2–0.8 μm. Anodizing, hardcoat, electroless nickel, black oxide and bead blasting all add steps and handling. Laser marking needs a minimum character height of 1.5 mm to stay readable. Mark only what the customer will actually read.

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  Name the alloy and temper"Aluminum" is not a specification.
• 2
  Separate cosmetic from functionalA brushed face and a sealing face are not the same job.
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  Call out maskingThreads and bores must be masked before anodizing.

For aerospace, automotive and medical buyers, the certificate list is a gate, not a nice-to-have. ISO 9001:2015 covers the general quality system. IATF 16949:2016 is what automotive programs usually ask for. ISO 13485:2016 applies to medical devices. ISO 27001:2022 covers information security, which matters when your drawings are confidential. Ask which one applies to your program and see it in writing.

A certificate does not tell you whether your part is correct. Ask for the inspection plan instead. A workable plan checks incoming raw material, monitors the process during the run, and inspects the finished part before shipment. For a first article, ask for a dimensional report showing measured values against nominal. For production, ask what sample rate the shop uses. If the answer is vague, that is your answer.

Confidentiality is a separate question, and it is a real one for defense and medical work. Uploads should be handled as confidential by default, and an NDA should be available on request. If a supplier cannot sign one before you send the drawing, move on.

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  Match the cert to the programISO 9001 is not a substitute for IATF 16949.
• 2
  Ask for measured valuesA pass/fail sheet hides the margin.
• 3
  NDA before drawingsNot after the quote arrives.

Two shops can quote the same five-day lead time and mean different things. Ask when the clock starts. A useful benchmark: quotation and free DFM analysis within 12 hours, production start within 24 hours, and parts shipping in 3–5 days. That sequence tells you the shop reviews the model before it cuts metal, which is where most delays are avoided.

Minimum order quantity is the other half. Some suppliers price a single prototype at a setup-heavy rate and push you toward a large first run. If you are still validating the design, that is the wrong trade. A shop that runs from one prototype to 10,000+ part runs lets you buy the information first and the volume later.

Judge the risk, not the promise. A supplier with a historical late-delivery probability below 2% is telling you something about scheduling discipline. Ask what happens when a tool breaks mid-run. The answer should describe a recovery step, not an apology.

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  Define day zeroPO receipt, DFM sign-off or material arrival.
• 2
  Prototype firstValidate the design before committing to volume.
• 3
  Ask about tool breakageThe recovery plan is the real lead time.