CNC Milling Services Georgia: How to Pick a Shop Without Rework

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  Six things that decide the quote
• 2
  What to compare before you send the PO
• 3
  Tolerance: what ±0.005 mm actually buys you
• 4
  Machine mix: three-axis, four-axis, or five-axis
• 5
  Lead time, MOQ, and what the quote clock really means
• 6
  Certifications and inspection: read the scope, not the logo
• 7
  Materials and finishing: where quotes quietly diverge
• 8
  How to qualify a milling supplier in six steps

A tolerance callout is a cost decision, not a quality badge. On a milled aluminum bracket, holding ±0.005 mm on a bearing bore is normal work. Holding the same band across a 300 mm bolt-hole pattern usually is not, because thermal drift and tool wear stack up faster than the machine error.

The practical move is to tolerance the features that mate. Give the machining supplier a datum scheme, a fit class, and a note on which surfaces are functional. Everything else can ride at a general tolerance. This single change often removes an entire inspection operation from the quote.

Surface finish follows the same logic. As-machined at Ra 1.6–3.2 μm is fine for most brackets and housings. Sealing faces and sliding surfaces may need Ra 0.8–1.6 μm, and optical or bearing seats can reach Ra 0.2–0.8 μm. Each step down adds passes and time.

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  Tolerance the fit, not the partCall out bores, pilots, and mating faces. Leave cosmetic surfaces loose.
• 2
  State the measurement methodCMM, bore gauge, or optical comparator. The method defines the number.
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  Watch thin wallsBelow 0.8 mm on aluminum, deflection moves the cut more than the machine does.

Three-axis milling moves the tool in X, Y, and Z. It is fast and cheap for prismatic parts with features reachable from one direction, or from a few sides with simple repositioning. A plate with drilled holes, a slot, and a flat pocket is three-axis work. Nothing is gained by putting it on a five-axis machine.

Four-axis adds rotation around one axis, usually A or B. Shafts with cross-drilled holes, parts with features on four faces, and cylinders with milled flats all fit here. The rotary table keeps the part in one setup, so hole-to-flat relationships hold without a re-clamp.

Five-axis moves the tool or the workpiece on two rotary axes at once. This is where undercut pockets, compound angles, and contoured surfaces stop being a fixturing problem. GreatLight runs 16 simultaneous five-axis centers with a Ø400 mm rotary table, plus travels up to 4,000 × 400 × 150 mm for long parts.

The buying question is not "do you have five-axis?" It is "which machine will cut my part, and how many setups?" Fewer setups means fewer datum shifts and a shorter inspection list. Ask for the setup count in the quote.

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  Three-axis fitsPrismatic plates, covers, housings, simple pockets.
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  Four-axis fitsShafts, cross-drilled parts, features on four sides.
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  Five-axis fitsUndercuts, compound angles, contoured or deep-cavity work.

Lead time conversations go wrong when two clocks get mixed. The first clock is quotation and DFM feedback, which should come back in 12 hours on a clean drawing. The second is production, which can start within 24 hours once the drawing is frozen and material is on hand. Parts typically ship in 3–5 days after that. Ask which clock a supplier is quoting.

Material availability drives most of the variance. Aluminum 6061 and 7075, stainless 303 and 304, and standard tool steels are routine. Inconel, titanium TC4 (Ti-6Al-4V), and beryllium copper can add days for stock. If your schedule is tight, ask the supplier to confirm stock before the PO, not after.

MOQ is the other silent cost. A shop with no minimum order quantity lets you buy one prototype and then a 10,000-part run without re-quoting the process. That matters for design validation, where the first part exists to prove the drawing, not to hit a price break.

Be careful with suppliers who quote a low unit price but add setup, programming, and fixture charges separately. Those charges do not disappear at volume. Ask for the full cost breakdown across three quantities: 1, 100, and 1,000 pieces.

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  Freeze the revisionA drawing change after setup restarts the schedule.
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  Confirm material stockEspecially for titanium, Inconel, and specialty alloys.
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  Compare three quantitiesOne, 100, and 1,000 pieces show the real cost curve.

A certificate on a website means little until you see the scope. ISO 9001:2015 covers quality management. IATF 16949:2016 applies to automotive production. ISO 13485:2016 applies to medical devices. ISO 27001:2022 covers information security, which is what protects your drawings and CAD files.

Ask for the current certificate and the scope statement. A shop certified for general machining may not be certified for the process you need, and the certificate will say so. If your part goes into a vehicle or a surgical device, the scope question is not optional.

Inspection is the second half of the same conversation. A supplier that runs 100% inspection before shipment, with raw material checks, in-process monitoring, and a final report on request, gives you a paper trail. That trail is what you hand to your own customer when they ask how the part was verified.

For confidential work, ask about the NDA and how uploads are handled. Drawings for an unreleased product should not sit in a shared folder. A signed NDA before you send the STEP file is normal practice, not a special favor.

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  Match cert to industryAutomotive, medical, and general industrial scopes differ.
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  Ask for the reportInspection data on request, not just a pass stamp.
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  NDA before the fileSign first, then send the model and drawings.

Two quotes for the same part can differ by 40% and both be honest. The gap is usually material grade and finishing. Aluminum 6061-T6 machines cleanly and is cheap. 7075 is stronger and gummier, so it cuts slower. Stainless 303 is free-machining; 316L is not, and 17-4PH in the H900 condition will fight a light finishing pass.

Titanium and nickel alloys change the whole cost structure. Ti-6Al-4V needs lower cutting speeds, more coolant, and sharper tooling. Inconel work-hardens if the feed is too light, so the programmer has to stay in the cut. These are not defects in the quote. They are the physics of the material.

Finishing is the second divergence. In-house anodizing, electroless nickel, zinc and silver plating, powder coating, bead blasting, and laser marking keep the part in one supply chain. If finishing is outsourced, add a logistics leg and a second inspection point. For laser marking, note that minimum character height is 1.5 mm, so plan your part numbers accordingly.

Before you compare prices, list the material condition, the finish spec, and the marking requirement on the RFQ. Quotes that answer the same question are the only ones worth comparing.

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  Name the condition6061-T6 and 7075-T6 behave differently from annealed stock.
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  Finish changes handlingAnodizing adds thickness; plan for it on threaded features.
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  Marking has a floorLaser character height 1.5 mm minimum.