Sourcing guide

How to Find CNC Machine Work That Matches Your Part

Most sourcing mistakes show up later as rework, not as a bad quote. This guide walks through the checks we would run before placing a job: drawing review, axis count, material stock, inspection method, and lead time. By the end you should be able to tell whether a shop can actually hold your tolerance before you send the PO.

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On this page

1
Key takeaways
2
Define the part before you shop for a supplier
3
Check whether the machine set can reach your geometry
4
Confirm the shop stocks your material and knows its behavior
5
Certifications, data handling and the questions buyers forget
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Step by step: how to find CNC machine work
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Part feature to machine type
8
What to verify before you place the order

Quick answer

Key takeaways

Start from the drawing, not the priceTolerance, datums and surface callouts decide which shop can run the part at all.

Match axis count to geometry3-axis covers 5 of 6 faces; undercuts and angled holes push you to 4 or 5 axes.

Ask how the part is measuredA tolerance you cannot inspect is a tolerance you cannot promise.

Stock size usually beats machine speedFor large parts, the question is who can hold 4,000 mm without re-fixturing.

Confirm post-processing in houseOutsourced anodizing adds days and a second set of hands on your parts.

Step zero

Define the part before you shop for a supplier

Before you search for how to find CNC machine work, write down what the part actually needs. Pull the critical dimensions off the drawing and mark the ones that carry function: bore diameters, mating faces, hole positions. A shaft with a ±0.05 mm journal is a different job from a bracket with a ±0.5 mm slot, even if both fit on the same machine.

Note the datum scheme. If the drawing dimensions from a corner that no fixture can reach, the shop will pick its own datum and you inherit the stack-up. Fixing datums on paper costs nothing. Fixing them after the first article costs a week.

List the material grade and condition. 6061-T6 cuts differently from 7075, and 17-4PH in the H900 condition will eat tooling. Grade changes are easy to overlook until the parts arrive at a different hardness than your mating component.

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Critical dimensionsMark the 5–10 features that carry function.
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DatumsState A, B and C so the fixture is not improvised.
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Material conditionTemper, hardness and any heat-treat step.

Capability

Check whether the machine set can reach your geometry

Axis count is the first filter. A 3-axis mill cuts from one direction, so you flip the part for the back side. That flip adds a setup, and each setup adds position error. For a plate with holes on two faces, 3-axis is fine. For a housing with ports on four sides plus a compound angle, you want 4 or 5 axes.

Simultaneous 5-axis matters when the tool has to stay normal to a curved surface or reach under a flange. If the feature can be indexed with the part stationary, a 4-axis mill with a rotary table does the same job for less money. Indexed 5-axis is not the same as simultaneous 5-axis, and quotes often blur the two.

Travel limits decide the rest. A part that fits inside 750 × 1,150 × 550 mm opens up most of a shop's capacity. Push past that and you are competing for the few large machines. At 4,000 mm, the number of shops that can run the part without re-fixturing drops sharply, and so does your scheduling flexibility.

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3-axisPrismatic parts, one or two setups, simple access.
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4-axisCylindrical or indexed features, holes around a bore.
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5-axisContoured surfaces, undercuts, compound angles in one setup.

Materials

Confirm the shop stocks your material and knows its behavior

Ask what the shop keeps on the floor. Aluminum 6061 and 7075, 303 and 304 stainless, and 1018 and 1045 steel are common stock. Exotics are not. Inconel, titanium Ti-6Al-4V and beryllium copper take different speeds, feeds and coolant strategy, and not every shop has run them.

Thin-wall aluminum is a classic trap. A 1 mm wall in a 100 mm pocket will move when you unclamp it unless the toolpath is planned around the distortion. If your part has thin ribs or long slender features, ask how they control deflection. A shop that answers with toolpath and support strategy is safer than one that answers with a tolerance number.

For plastics, heat is the limit. PEEK and carbon fiber composites need sharp tooling and conservative depth of cut, or you get delamination and melted edges. POM machines cleanly but moves with temperature, so it should be measured after it stabilizes, not straight off the machine.

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Common stock6061, 7075, 303/304, 1018, 1045, brass.
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Exotic alloysInconel, Ti-6Al-4V, beryllium copper. Ask for prior parts.
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Thin wallsUnder 1.5 mm needs a distortion plan, not a tighter tolerance.

Risk

Certifications, data handling and the questions buyers forget

Certifications tell you which management systems are audited. ISO 9001 covers general quality process. IATF 16949 applies to automotive production. ISO 13485 covers medical devices. ISO 27001 covers information security, which matters if you are sending CAD files with proprietary geometry.

Ask for the certificate scope, not just the logo. A shop can hold ISO 9001 for one site and run your parts at another. If your industry needs IATF or ISO 13485, confirm the site that will actually machine the parts is in scope.

Data handling is a real risk in contract machining. Files move between CAM programmers, machine operators and inspectors. A shop with ISO 27001 has defined access controls and retention rules. If you need an NDA, ask before you upload, not after.

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ISO 9001:2015Baseline quality management, most common requirement.
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IATF 16949:2016Automotive production, includes traceability expectations.
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ISO 13485:2016Medical devices, document and process control.
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ISO 27001:2022Information security for your CAD and IP.

How-to

Step by step: how to find CNC machine work

Run these in order. Each step filters out shops before you spend time on quotes.

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1. Write a one-page part briefInclude material and temper, the 5–10 critical dimensions, tolerances, surface finish (Ra 0.8–1.6 μm is a common fine-machined target), quantity and target date. Attach STEP and PDF. This single page removes half the back-and-forth.
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2. Sort shops by axis count and travelFilter out anyone whose largest machine is smaller than your part envelope. For a 600 mm part, a shop with a 500 × 500 × 450 mm travel cannot run it in one setup. Ask for the actual machine list, not a general capability claim.
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3. Ask how the critical features will be inspectedCMM, optical comparator, micrometer, gauge pins. If a ±0.005 mm bore is called out, the shop needs a CMM or a bore gauge with the right resolution. A caliper is not an inspection method for that tolerance.
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4. Request a DFM review before the quoteA good shop flags features that are hard to hold: deep pockets under 3× tool diameter, sharp internal corners, tolerances tighter than the process can repeat. Fix these on paper and the first article passes sooner.
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5. Confirm post-processing and finishAnodizing, plating, powder coating and laser marking change dimensions slightly. Hardcoat anodize can add 25–50 μm per surface. State whether the finish is cosmetic or functional, and whether masked areas need bare metal.
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6. Ask what happens when a dimension driftsThe answer should be a process, not a promise. In-process monitoring, first-article inspection, and a plan to stop and call you rather than ship and hope. Ask who signs the inspection report.
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7. Run one small order before the big oneOrder 1–5 parts, inspect them against the drawing, then scale. This is the cheapest way to test a shop's communication, packaging and finish quality. If the sample order is late or undocumented, the production run will be worse.

Selection table

Part feature to machine type

Use this table before you ask for a quote.

Part feature	Machine type	Why
Flat plate, holes on one face	3-axis	Single setup, no repositioning
Holes on four sides of a block	4-axis with rotary table	Indexed rotation, one datum
Curved blade or impeller	Simultaneous 5-axis	Tool stays normal to surface
Deep pocket with undercut	5-axis or EDM	Straight tool cannot reach
Turned shaft with cross holes	Mill-turn center	Turning and milling in one setup
Part over 1,200 mm long	Large-travel machine	Avoids re-fixturing and blend error

Due diligence

What to verify before you place the order

What to check	What good looks like	Red flag
Tolerance vs. inspection	CMM or gauge for every critical callout	Calipers on a ±0.005 mm feature
First article	Documented report before full run	Ship first, inspect later
Finish supplier	In-house or named partner	Vague answer on who anodizes
File security	Access controls, NDA on request	Files sent over personal email
Scheduling	Named machine and start date	No commitment on capacity
Nonconformance	Written process and owner	Fix it quietly and reship

The short version

Pick the shop whose machine list, inspection method and finish supply chain match your drawing. Price and lead time only matter after those three line up.

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FAQs

Questions engineers ask before ordering

How do I know if my part needs 3-axis, 4-axis or 5-axis machining?

Count the directions the tool has to approach from. If all features are reachable from one or two orthogonal directions, 3-axis works. If features are arranged around a bore or indexed at 90° intervals, 4-axis saves a setup.

Simultaneous 5-axis is for contoured surfaces, undercuts and compound angles that have to be cut without repositioning the part. If the feature can be indexed and then cut, a 4-axis machine is usually the cheaper choice.

What tolerance should I put on the drawing?

Put the tolerance the function needs, not the tightest number you have seen. A ±0.005 mm callout on a non-critical clearance hole adds cost and inspection time with no benefit.

Reserve tight tolerances for mating features, bearing seats and alignment datums. For general surfaces, ±0.1 mm and Ra 1.6–3.2 μm is often enough.

How many parts should I order for a first run?

Start with 1–5 pieces to validate the process, the finish and the documentation. Once the first article passes, scale to the production quantity.

There is no minimum order quantity here, so a single prototype and a 10,000-part run go through the same quoting path.

What lead time is realistic for a machined part?

Quotation and DFM analysis come back within 12 hours, production can start within 24 hours, and parts typically ship in 3–5 days. That timing assumes the drawing and material grade are final.

If the part needs an exotic alloy outside normal stock or a multi-step finish, add time for material procurement and outside processing.

Can a shop hold a tolerance on a thin-wall part?

It depends on wall thickness and geometry. Walls under 1.5 mm in aluminum will deflect under clamping and cutting forces unless the toolpath and workholding are planned for it.

Ask for the strategy: rough, stress-relieve, then finish. If a shop quotes a thin-wall part without discussing deflection, expect to measure out-of-round parts.

What documents should come with the parts?

At minimum, a packing list and an inspection report covering the critical dimensions. Ask for material certification if traceability is required by your industry.

100% inspection before shipment is standard here, covering raw material check, in-process monitoring and final inspection. Reports are available on request.