NYC CNC Processing Service Guide

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  Key takeaways
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  What to compare across NYC machine shops
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  Set tolerances from the drawing's function
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  Match the machine to the part geometry
• 5
  Materials, finishes and what they add to the schedule
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  Certifications, inspection and confidentiality
• 7
  Read the quote like a cost breakdown
• 8
  Seven steps to place a clean order

The first question in any NYC CNC processing service guide is what the part actually has to do. A bearing bore and a cover plate do not deserve the same callout. When a drawing carries a blanket ±0.005 mm note, every feature is inspected to that band, cycle times rise, and the quote reflects work the part never needed. Mark the critical dimensions, then let the rest sit at general machining tolerance.

Material changes the achievable band. Aluminum 6061 and 7075 cut cleanly and hold ±0.005 mm without drama. Stainless 316 and 17-4PH move more under tool pressure, so thin walls need lighter passes and sometimes a stress-relief step between roughing and finishing. Titanium TC4 (Ti-6Al-4V) and Inconel push tool wear up, which shows in both price and schedule.

Surface finish is a separate line item. As-machined parts sit around Ra 1.6–3.2 μm. A sealing face or a sliding surface may need Ra 0.8–1.6 μm, and optical or medical contact surfaces can reach Ra 0.2–0.8 μm. Each step down needs a different cutter and a slower pass. Put the finish callout on the specific face, not on the whole drawing.

Here is the practical test. Send the shop a drawing with three marked critical dimensions and ask what band they will hold on each one, and how they will measure it. A shop that answers with a method, not just a number, is telling you how it will run the job.

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  Tight only where it countsBlanket ±0.005 mm across a whole part raises cost with no functional gain.
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  Finishes travel in stepsRa 1.6–3.2 μm as-machined; Ra 0.8–1.6 μm needs a finishing pass; Ra 0.2–0.8 μm is a separate operation.
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  Ask for the measurement methodCMM, micrometers and pin gauges answer different questions.

Geometry decides which machine the job belongs on, and that decides the price. Simple prismatic plates with holes on one face run fastest on a 3-axis mill. Parts with features on four sides, such as manifolds or valve bodies, need a 4-axis or a tombstone setup to cut handling time. When you see compound angles, deep pockets reached from two directions, or a bore that must stay coaxial with a face, that is 5-axis work.

The value of 5-axis is not a nicer surface. It is fewer setups. Every re-fixturing step adds datum error, and datum error is what turns a ±0.005 mm callout into a debate at incoming inspection. On a simultaneous 5-axis center, an impeller, a medical housing or a robot wrist bracket can come off the table complete. Mill-turn centers do the same for round parts that also carry milled flats and cross holes.

Work envelope limits are worth checking early. GreatLight runs travel up to 4,000 × 400 × 150 mm for long parts, 750 × 1,150 × 550 mm and 600 × 600 × 600 mm for mid-size housings, and 500 × 500 × 450 mm or 500 × 310 × 200 mm on compact machines. A Ø400 mm rotary table covers most round work. If your part sits outside those boxes, say so before the quote, not after.

One caution. Five-axis does not fix a bad datum. If the drawing has no clear A-B-C datum scheme, the shop will pick one, and it may not be the one your assembly needs. Define datums before release.

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  3-axis for flat platesHoles and pockets on one face, no compound angles.
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  4-axis for four-sided workManifolds and valve bodies indexed on a rotary table.
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  5-axis for compound featuresImpellers, medical housings, coaxial bores reached from two directions.
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  Mill-turn for round plus milledShafts with cross holes and flats in one cycle.

Material availability quietly sets the real lead time. Common grades such as aluminum 6061-T6, 304 stainless, 1018 steel and C36000 brass are usually on the shelf. Grades like 17-4PH (SUS630), 4340, beryllium copper, Inconel and magnesium AZ31B or AZ91D may need a mill order, which adds days before the first chip. Tell the shop if an equivalent grade is acceptable; sometimes it is, and sometimes the substitution changes the heat treat or the corrosion behavior.

Finish choice follows function. Anodizing in clear, color, hardcoat or conductive form suits aluminum housings and covers. Electroless nickel holds tight dimensional tolerance better than most plating and is a common pick for wear surfaces. Zinc plating, silver and gold plating serve electrical and RF parts. Powder coating and black oxide are cosmetic or corrosion barriers. Bead blasting, tumbling, brushing and polishing change appearance and can also deburr edges that would otherwise fail inspection.

Two details cause most finish disputes. First, masking. If a threaded hole or a grounding pad must stay bare, mark it on the drawing; anodizing and plating will coat it otherwise. Second, laser marking. Minimum character height is 1.5 mm, so a 0.8 mm serial number will not be legible no matter how good the laser is.

Heat treat and finish interact too. Hardened 4140 or 440C should be finished before hardening where possible, because post-hardening cutting is slow and expensive. Plan the sequence, not just the operations.

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  Check stock before promising a dateExotic grades can add days before machining starts.
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  Say what must stay bareMask threads and grounding pads on the drawing.
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  Laser marking has a floor1.5 mm minimum character height.

Certificates matter only when they cover the plant doing your work. Ask which site machines the parts and which certificate numbers apply there. ISO 9001:2015 is the baseline for general industrial work. IATF 16949:2016 is what automotive and EV buyers look for. ISO 13485:2016 applies to medical device work. ISO 27001:2022 covers information security, which is the one that answers the question your IT team will ask about CAD files.

Inspection is where the tolerance claim becomes evidence. GreatLight inspects 100% of parts before shipment, covering raw material check, in-process monitoring and final inspection, with reports on request. The qualification rate is 99.99%. That is a claim about process control, not a promise that every dimension on a difficult part will land inside ±0.005 mm on the first run. On a new geometry, expect a first-article inspection and a conversation.

Confidentiality is a real selection criterion for defense, medical and consumer electronics programs. Uploads are handled as secure and confidential, and an NDA is available on request before files move. Do not send production files to a personal email address, and do not accept a supplier who treats an NDA as an insult.

One more check: how the shop handles a nonconformance. Ask what happens when a dimension is out. A supplier with a documented containment and rework path will tell you the process. A supplier who says it never happens is telling you something else.

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  Match certificate to industryISO 9001 general, IATF 16949 automotive, ISO 13485 medical, ISO 27001 data.
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  Ask for the inspection planRaw material, in-process and final stages, with reports on request.
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  NDA before files moveAvailable on request; use a company channel, not a personal inbox.

A price per piece hides where the money goes. Ask for the quote split into material, machining time, setup, finish and inspection. Setup dominates small orders. Machining time dominates large ones. If a quote looks low on a 5-axis part, either the shop is planning fewer setups than you assumed, or it missed a feature.

Volume changes the answer. From one prototype up to a few hundred parts, the fastest route is usually machining from billet or plate. Above that, die casting or vacuum casting can win on piece price, but only after the tooling cost is amortized and only if the geometry suits a mold. If your annual volume is uncertain, ask for both routes priced side by side before committing to a tool.

Lead time is three clocks, not one. Quotation and free DFM analysis land within 12 hours. Production can start within 24 hours after release. Parts ship in 3–5 days for straightforward work. Complex geometry, exotic material or a multi-step finish will push the last number, and a shop that tells you so upfront is more useful than one that quotes an aggressive date and then explains the slip.

The historical late-delivery probability at GreatLight is below 2%. That is a track record, not a guarantee for your specific part. Build a buffer on the critical path and keep the shop informed when your assembly date moves.

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  Ask for a line-item quoteMaterial, setup, machining, finish, inspection separated.
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  Price both routes at volumeMachining versus casting, before you pay for tooling.
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  Treat lead time as three clocksQuote, production start and shipping are separate dates.