Vertical CNC Milling Service Guide for Engineers and Buyers

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  Key takeaways
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  Which machine type fits your part
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  What a vertical CNC milling service actually gives you
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  Five checks before you award a vertical CNC milling service
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  Travel, table size and the part that does not fit
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  What actually drives the price of a vertical CNC milling job
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  MOQ, lead time and the questions to ask a supplier
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  How to prepare a vertical CNC milling RFQ

In a vertical machining center the spindle points down and the workpiece sits on a horizontal table. Chips fall away from the cut, so the operator can see what is happening and the tool does not recut the same chips. That single geometry choice explains most of the strengths and limits of a vertical CNC milling service.

The trade-off is reach. A VMC works best when the part can be approached from above. Deep side pockets, undercuts and internal bores that run sideways usually need a right-angle head, a second setup, or a different machine. If a drawing needs five faces machined and three of them face sideways, you are comparing setup count, not machine price.

Most shops quote a VMC by the part, not by the hour, but the hour still drives the number. Setup, fixturing, CAM programming and inspection are fixed costs per order. A part with a 6-minute cycle can still be expensive if it needs four setups. A part with a 40-minute cycle on one setup is often the cheaper job.

Spindle speed and torque matter more than the brochure's maximum rpm. Aluminium wants 10,000–15,000 rpm and light radial engagement. Steel and titanium want torque at 2,000–6,000 rpm. A shop that lists one spindle spec for every material is telling you something about its process control.

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  Spindle orientationDownward tool axis, gravity-assisted chip clearing, easy part access.
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  Work envelopeX, Y and Z travel plus table load limit, not just table dimensions.
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  Setup countEvery re-fixture adds positional error and labor time.

Tolerance is the first check, but the number alone is not the answer. Ask what the ±0.005 mm applies to: a drilled hole, a bored bore, a milled slot, or a datum-to-datum dimension across 300 mm. A shop that can hold ±0.005 mm on a 50 mm feature may not hold it across a 1,000 mm part once thermal growth enters the picture.

Second, ask how the tolerance is verified. Calipers and micrometers are fine for a quick check but they do not prove position. A CMM report, a height gauge with granite plate, or a optical comparator tells you the shop measured the feature that matters. Request the inspection report format before the order, not after.

Third, check the material list against your drawing. Aluminium 6061 and 7075 machine very differently. 7075 holds a better finish but is more prone to stress movement after heavy material removal. Titanium Ti-6Al-4V and Inconel need lower surface speed, more coolant and sharper tools. A supplier that lists every material without process notes is quoting from a catalog, not a shop floor.

Fourth, look at finishing options. As-machined Ra 1.6–3.2 μm is normal for a VMC. Ra 0.8–1.6 μm needs a finer stepover and a sharp tool. Ra 0.2–0.8 μm usually means a separate finishing pass, a different tool, or a secondary process. If the drawing calls for a cosmetic surface, say so on the RFQ; it changes the cycle time.

Fifth, confirm certifications match your industry. ISO 9001:2015 covers general quality management. IATF 16949:2016 is the automotive standard. ISO 13485:2016 applies to medical devices. ISO 27001:2022 covers information security. A supplier holding all four is set up to handle different traceability and documentation demands without a scramble.

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  Tolerance scopeWhich feature, over what distance, measured how.
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  Inspection methodCMM, height gauge or comparator; ask for the report format.
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  Material process notesSpeeds, coolant and tooling differ by alloy, not just by name.
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  Finish expectationRa value and cosmetic requirement change cycle time.

A machine's table size is not its cutting envelope. A 1,200 × 600 mm table may only have 1,000 × 500 mm of X and Y travel once the vise, fixture and tool change positions are accounted for. Always ask for the travel figures and the maximum part weight the table can carry without deflection.

GreatLight runs a range of VMC sizes: a 4,000 × 400 × 150 mm travel for long rails, 750 × 1,150 × 550 mm and 600 × 600 × 600 mm for mid-size housings, and 500 × 500 × 450 mm or 500 × 310 × 200 mm for compact parts. A Ø400 mm rotary table handles 4-axis indexing on round and prismatic work.

The common mistake is sending a part that fits the table but not the travel. A 900 mm long part on a machine with 800 mm X travel cannot be machined in one setup, even though it sits on the table. The quote will come back with a second setup, or the shop will decline.

Weight matters too. A heavy steel block on a small table can sag the table and lose Z accuracy over the cut. For dense materials above roughly 200 kg, confirm the table load rating and consider whether a larger machine is the better match.

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  Ask for travel, not table sizeX, Y and Z travel define what can be cut in one setup.
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  Check part weightTable load limits protect Z accuracy on dense materials.
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  Long parts need long travelA 4,000 mm envelope is unusual; confirm before quoting.

Setup count is the biggest lever. One setup with a good vise or soft jaws is fast. Two setups need a flip and a re-datum. Three or more setups need fixtures, and fixtures cost money whether you order one part or one hundred. If a design can be changed to reduce setups without losing function, do it before the RFQ.

Cycle time is the second lever. The material removal rate depends on spindle power, tool rigidity and the depth of cut the setup can tolerate. A thin wall or a tall feature that needs support will force light passes, which stretches the cycle. Engineers who flag thin walls and deep pockets on the drawing help the shop quote accurately.

Tooling availability is the third. A standard Ø10 mm end mill is on the shelf. A custom form tool or a long-reach tool may need ordering, which adds days. If the part needs a non-standard thread or a special profile, mention it early.

Volume changes the math. For one to ten parts, programming and fixturing dominate. For 10,000+ parts, cycle time and tool life dominate. A shop that quotes both the same way is not looking at your volume.

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  SetupsEach re-fixture adds labor and positional error.
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  Cycle timeThin walls and deep pockets force light passes.
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  ToolingSpecial tools add lead time, not just cost.

Minimum order quantity tells you how a shop is organized. A supplier with no MOQ runs prototype and low-volume work alongside production. That matters when you need three parts next week and the shop's schedule is full of 10,000-piece runs. GreatLight quotes from one prototype to 10,000+ part runs with no minimum order quantity.

Lead time has several parts: quotation, DFM feedback, material ordering, machining, finishing and inspection. Ask for each separately. A quotation and free DFM analysis within 12 hours is realistic for a well-equipped shop. Production can start within 24 hours once the order is confirmed. Parts ship in 3–5 days for standard jobs.

Ask what happens when a feature is out of tolerance. A good answer describes rework or remachining, not a credit note. Ask whether inspection is 100% before shipment. Ask whether raw material certificates come with the parts. These are process questions, and the answers reveal whether the shop controls its own quality.

Confidentiality matters for new products. Uploads should be secure and confidential, and an NDA should be available on request. If a supplier hesitates on an NDA for a pre-launch design, treat that as a signal.

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  MOQNo minimum means prototypes do not wait behind production runs.
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  Lead time breakdownQuote, DFM, material, machining, finishing, inspection.
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  Out-of-tolerance planRework beats a credit note when your schedule is tight.
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  NDA and upload securityPre-launch designs need both, in writing.