Industrial Web Search Buyer's Guide Sector
Contract manufacturing of machined components to a customer's drawing, using computer-controlled milling, turning, and multi-axis equipment. This sector covers the machining itself, as well as the inspection, documentation, and external processes that determine whether the finished part is accepted.
Overview
A working orientation to the sector before you approach specific shops: how machining capability is classified, what actually drives cost and lead time, and the kinds of company you will end up talking to.
Machining can be categorized primarily by process. In milling, material is removed using a rotating cutter while the part remains stationary. In turning, the part is rotated against a fixed tool. Most shops offer both processes. However, for buyers, a more useful distinction lies in the axis count and configuration.
Three-axis milling is well suited to many prismatic features accessible from a limited number of orientations. More complex geometry can still be machined through multiple setups; five-axis machining can reduce setups and improve access where the geometry justifies it. This method can produce complex geometries with fewer setups, enhancing feature accuracy and reducing lead time, albeit at a higher machine rate. Turning centers equipped with live tooling combine turning and milling in a single setup, while Swiss machines are designed for slender parts and enable precise work on small diameters.
When it comes to pricing a part, three key factors come into play: tolerance (which is the largest cost driver after material and quantity, as it dictates the machine class, inspection requirements, and scrap rate), the number of setups needed, and any external processes such as heat treatment, plating, or non-destructive testing. These external processes can add both time and dependencies to the supply chain. Therefore, a shop's true capability is defined by the combination of its machinery, inspection equipment, and the processes it can control or reliably source.
There are three main types of companies operating in this sector. Job shops typically machine parts to a customer's specifications in low- to moderate-volume production, making them well-suited for prototypes, replacement parts, and short runs. Production machining suppliers are geared towards repeat volume, utilizing dedicated fixtures and process controls, with pricing structured around annual quantities rather than individual orders. Contract manufacturers provide machining as part of a broader service that may include assembly, sourcing of purchased components, finishing, and supply chain management. This distinction is important because it affects both the pricing structure and the responsibility for addressing issues: a job shop quotes based on the specific part in front of them, a production supplier prices based on maintaining a relationship, and a contract manufacturer takes on responsibilities beyond just the machined part.
Sourcing Considerations
The decisions below are the ones that most often cause regret later. The detail sits in the guides at the bottom of this page.
Tolerance is often one of the largest controllable cost drivers. Every step tighter demands better machines, slower cycles, more inspection, and produces more scrap. Tolerances copied from a previous drawing or applied uniformly across a part are the most common reason quotes come back higher than expected. Tighten only what the function requires, and leave everything else open.
A model without a drawing leaves tolerance and finish undefined. A drawing without quantities leaves pricing to guesswork. Incomplete packages do not stop a shop from quoting; they prompt the shop to make assumptions, which later surface as change orders.
A quality certification applies to a defined scope, not to everything a company does. Confirm it covers the processes and the specific facility your part will pass through, confirm it is current, and where a public registry exists, verify it there rather than relying on a certificate supplied by the shop.
Heat treatment, plating, anodizing, welding, and non-destructive testing cannot be verified by inspecting the finished part, so they are controlled by accrediting the processor. A machining supplier's own quality certification does not extend to its outside processors. Ask who performs these operations and what accreditation they hold.
Material certifications, first-article inspection reports, dimensional data, and traceability records all require work to produce, and a shop prices differently when it knows they are required. Deciding what documentation you need after parts are made is expensive, and sometimes impossible if the records were never kept.
Prototype quantities carry the full weight of programming and setup, so a per-part price at quantity five tells you little about the price at quantity five hundred. Ask for both, and be explicit about whether prototypes must be production intent or whether a faster method is acceptable.
Glossary
The terms you will meet on a drawing, a quote, or a supplier audit, in plain English.
A supplier statement that the parts shipped meet the requirements of the purchase order and drawing. It is a declaration rather than measured evidence, so it is not a substitute for inspection data when dimensional proof is required.
A machine that measures part geometry by probing points and comparing them against the model or drawing. CMM capability determines whether a shop can verify tight tolerances and geometric callouts at all, and its calibration records are part of the evidence behind any inspection report.
A reference point, line, or plane on the part from which other features are located and measured. Datums establish how the part is held and measured, so a poorly chosen datum scheme can make a drawing expensive or impossible to inspect even when every tolerance on it is reasonable.
Removing the sharp edges and raised material left by machining. It is a real operation with real labor cost. Drawings that leave the edge condition undefined are a common source of dispute during inspection because the buyer and the shop assume different things.
Reviewing a design against how it will actually be machined, to identify features that are expensive, risky, or unnecessary. A shop that offers DFM feedback before quoting is frequently worth more than one that quotes the drawing exactly as drawn.
The quantity you expect to order over a year. It affects pricing more than the size of the individual order, because setup and programming cost can be spread differently when a shop knows repeat work is coming. Providing it, or stating plainly that it is unknown, produces a more useful quote.
A documented inspection of the first part produced from a new or changed process, verifying that every drawing characteristic has been met. It does not by itself establish long-term process capability or production consistency.
Five-axis machines provide motion about or along five axes. Some work is indexed 3+2 machining, while simultaneous five-axis machining coordinates all axes during cutting. Fewer setups generally mean better feature accuracy and shorter lead time, at a higher machine rate.
The tooling that holds a part in position during machining. Custom fixtures are frequently required for complex or higher-volume parts and are usually a separate one-time cost. Whether the shop or the buyer owns the fixture should be settled before the order, not after.
Any loose material that could damage a product or system, such as chips, tooling fragments, or packaging. FOD control is a formal requirement in aerospace work, covering cleaning, inspection, and packaging practice, and it is one of the requirements aerospace quality systems add over general ones.
A symbolic system for defining permitted variation in a part's form, orientation, location, and profile, rather than relying on plus and minus dimensions alone. Used correctly, it states functional intent precisely and is often what makes a tight-tolerance part manufacturable at reasonable cost.
The time from order placement to delivery, covering programming, material procurement, machining, outside processing, and inspection. Material availability and outside processes frequently drive it more than machining hours do, which is why lead time and price should be quoted together.
Powered tools on a lathe that allow milling, drilling, and tapping while the part remains in the turning machine. Combining operations in one setup reduces handling and improves the positional relationship between turned and milled features.
Documentation from the material producer stating chemical composition and mechanical properties, tied to a heat or lot number. It is the link between the finished part and the material it was made from, and it is the first thing an auditor asks for on regulated work.
A part or condition that does not meet the specified requirement. What matters to a buyer is the process around it: how the shop identifies, documents, segregates, and dispositions nonconforming parts, and whether you are notified before anything ships.
One-time costs incurred before production, typically programming, fixture design and build, and first article inspection. NRE is quoted separately from the per-part price, and understanding the split is essential to comparing quotes fairly.
A structured submission demonstrating that a production process can consistently make parts to specification. It originated in automotive and has an aerospace counterpart. It is a documentation package rather than a single inspection, so knowing whether one is required changes both cost and timeline.
A prototype proves the design works. A production-intent part is made using the process, materials, and tooling planned for volume production. Parts that pass as prototypes can fail when the process changes for volume, which is why the distinction belongs in the RFQ rather than being discovered later.
The arithmetic mean roughness of a surface, the most commonly specified surface finish parameter. It appears on almost every drawing that calls out finish, though it describes only one aspect of surface texture, and the standard used to measure it affects the reported value.
One fixturing of the part on a machine. Each additional setup adds handling, introduces potential positional errors between features, and increases cost. Reducing setups is one of the main reasons multi-axis machines command higher rates.
Special processes require qualified, controlled processes because final inspection alone cannot fully verify the result. Depending on the industry and contract, control may include approved processors, Nadcap accreditation, customer approval, process specifications, lot traceability, test coupons, and certification records.
Turning on a machine with a sliding headstock and guide bushing that supports the material close to the cutting tool. Suited to small-diameter, long, and slender parts where conventional turning would deflect, and common in medical and connector work.
The permitted variation on a dimension. It is the largest driver of machining cost after material and quantity, because tighter tolerances demand better machines, more inspection, slower cycles, and produce higher scrap rates.
The accumulation of individual tolerances across multiple features or parts in an assembly. Individually reasonable tolerances can combine into an assembly that will not fit, which is why stack-up analysis belongs in the design stage rather than at inspection.
The ability to link a finished part back through manufacturing records to the material heat or lot it came from. Required in aerospace, defense, and medical work, and it depends on the shop's record system rather than on any single document.
The document that accompanies a job through the shop, recording each operation, who performed it, and inspection results. Also called a router or work order. It is the primary record an auditor reviews and the evidence behind a certificate of conformance.
The maximum part size a machine can accommodate in each axis. Parts near the limit of a shop's envelope may require workarounds or a different supplier, so it is worth confirming early rather than assuming a shop can hold your largest part.
Standards
What each standard governs and why a buyer should care. Which ones apply depends on your industry, the drawing you are working on, and whether the work is export-controlled.
Quality management systems
Published by the International Organization for Standardization. The general quality management system standard, covering documented processes, corrective action, and continual improvement. It is the baseline most machine shops hold. It says the shop manages quality systematically; it says nothing about machining or tolerance capability.
Published by SAE International in coordination with the International Aerospace Quality Group. AS9100 adds aerospace quality-management requirements. When a formal aerospace first article is contractually required, AS9102 defines the standard reporting format, including configuration management, counterfeit part prevention, foreign object debris control, product safety, first article inspection, and special process controls. Certification scope can be verified in the IAQG OASIS database rather than taken on the strength of a supplied certificate.
Published by the International Organization for Standardization. The quality management standard for medical devices, emphasizing risk management, documentation, and traceability. Required by most medical device manufacturers of their component suppliers, and structured differently enough from ISO 9001 that holding one does not imply the other.
Published by the International Automotive Task Force in association with ISO. The automotive quality management standard, built on ISO 9001 and adding requirements around defect prevention, process control, and supply chain management. Relevant if your parts enter automotive production.
Drawings, tolerancing, and measurement
Published by ASME. The American standard for dimensioning and geometric tolerancing, defining the symbols and rules of GD&T. The 2018 edition replaced the 2009 edition and removed the concentricity and symmetry symbols, among other changes. Because editions differ in interpretation, a drawing should state which edition applies.
Published by the International Organization for Standardization. The Geometrical Product Specifications system, including ISO 8015 for fundamental rules and ISO 1101 for symbols and rules of use. It is the international counterpart to ASME Y14.5, and the two differ in some fundamental principles, so a drawing must state which system governs.
Published by the International Organization for Standardization. General tolerance standards covering dimensions that are not individually toleranced. ISO 22081 replaced ISO 2768-2, moving away from fixed tolerance tables toward a framework requiring the designer to define general tolerances explicitly. ISO 2768-1 remains in use for linear and angular dimensions. Both still appear on drawings, so confirm which is being invoked.
Published by the International Organization for Standardization and ASME respectively. Surface texture standards. ISO 21920, published in 2021 in three parts, replaced ISO 1302, ISO 4287, ISO 4288, and ISO 13565-2 and -3, all of which were withdrawn. Parameter definitions are largely retained, but the calculation method changed for several parameters, so the same surface can report a different value depending on which standard the measurement followed. ASME B46.1 is the US standard. Drawings issued before the change remain valid under the former standards.
Published jointly by the International Organization for Standardization and the International Electrotechnical Commission. The competence standard for testing and calibration laboratories. Relevant because a shop's inspection results are only as trustworthy as the calibration behind its measuring equipment, and accredited calibration is what makes that traceable.
Aerospace, defense, and special processes
Published by SAE International. Defines the aerospace first article inspection requirement and its reporting format, using standardized forms that record every drawing characteristic with its measured value. A completed report in this format, with a ballooned drawing and material certifications attached, is what a prime contractor expects, rather than a signed statement that the part was checked.
Administered by the Performance Review Institute. An industry-managed accreditation program for special processes including heat treatment, chemical processing, welding, and non-destructive testing. It exists because these processes cannot be verified by inspecting the finished part. A shop holding AS9100 is not thereby accredited for special processes; those require separate Nadcap accreditation, verifiable through the program's public listing.
Administered by the US Department of State Directorate of Defense Trade Controls. The International Traffic in Arms Regulations govern defense articles and technical data. Under 22 CFR Part 122, US companies manufacturing defense articles must register with the DDTC even when no export occurs. Registration is a compliance status rather than a quality certification, and it says nothing about machining capability.
Published by the National Institute of Standards and Technology and the US Department of Defense. NIST SP 800-171 defines the security controls protecting Controlled Unclassified Information, DFARS 252.204-7012 makes them contractually binding, and the Cybersecurity Maturity Model Certification provides third-party verification, with CMMC Level 2 mapping to those controls. These are distinct from ITAR: a supplier can be ITAR-registered and still not meet cybersecurity requirements because the two address different things.
Published by the US Department of Defense. Restricts acquisition of specialty metals, including certain steels, titanium, and alloys, requiring that they be melted in the United States or a qualifying country and documented accordingly. Compliance is established at the material level through mill certifications upon receipt, not at the finished-part level.
Frequently Asked Questions
Direct answers to the questions buyers ask most often when sourcing in this sector.
Only as tight as the function requires. Tolerance is often one of the largest controllable cost drivers, alongside material, part geometry, setup count, cycle time, quantity, and special-process requirements. The most common and most expensive mistake is applying a uniform tolerance across an entire part, or carrying tolerances forward from a previous drawing without reviewing them. Identify the features that actually control fit, sealing, or alignment, tighten those, and open everything else. If you are unsure, ask a shop for design-for-manufacturability feedback before finalizing the drawing, rather than after receiving the quote.
AS9100 incorporates ISO 9001 in its entirety and adds aerospace-specific requirements on top. Those additions include configuration management, counterfeit part prevention, foreign object debris control, product safety, first article inspection, and controls over special processes. A shop holding ISO 9001 has a systematic quality management system. A shop holding AS9100 has that plus the aerospace layer. Neither tells you anything directly about machining capability, tolerance capability, or inspection equipment, which have to be assessed separately.
No, and this is a common and costly misunderstanding. Special processes are operations whose results cannot be verified by inspecting the finished part, such as heat treatment, chemical processing, welding, and non-destructive testing. Because the outcome is not directly inspectable, it is controlled by accrediting the processor rather than by the machining supplier's own certification. In aerospace, this is handled through Nadcap accreditation, administered by the Performance Review Institute. Ask which special processes your part requires, who performs them, and what accreditation that processor holds.
A first article inspection is a documented verification that the first part from a new or changed process meets every characteristic on the drawing. It demonstrates that the process can produce the part as specified, rather than that one part happened to be acceptable. It is required in aerospace, where AS9102 defines the format, and is commonly requested in medical, defense, and other regulated work. A strong report measures every drawing characteristic with actual values, references a ballooned drawing, includes material certifications, and ties back to the drawing revision. A signed statement confirming that the part was checked is not a first-article inspection.
At minimum: a drawing with tolerances and finish requirements, a 3D model, the material specification, the quantity for this order and the expected annual usage, and the delivery requirement. Beyond that, state what documentation you need, whether material certifications or inspection data are required, whether the parts are production-intent or prototypes, and any certifications the supplier must hold. Incomplete packages do not stop a shop from quoting. They cause the shop to make assumptions, which then become change orders after the order is placed.
They address different things and neither substitutes for the other. ITAR registration with the Directorate of Defense Trade Controls concerns the export control of defense articles and technical data and, under 22 CFR Part 122, applies to US manufacturers of defense articles even when nothing is exported. A U.S. person engaged in the business of manufacturing, exporting, temporarily importing, or brokering defense articles or defense services generally must register with DDTC, subject to the specific regulatory definitions and exemptions. Registration does not itself confer export authority or demonstrate technical capability. CMMC, built on the security controls in NIST SP 800-171 and made contractually binding through DFARS clauses, concerns cybersecurity for Controlled Unclassified Information. A supplier can be ITAR registered and still fail to meet cybersecurity requirements. If your program involves both controlled technical data and CUI, verify each separately.
Because programming, fixture design, and first-article inspection are one-time costs and, at prototype quantities, are spread across very few parts. At volume, the same costs are spread across many, and the shop can justify dedicated tooling and process optimization that would not be worth it for five parts. A per-part price at prototype quantity is therefore a poor predictor of production price. Ask for both, and have the one-time costs quoted separately so you can compare suppliers on the same basis.
It depends on what the drawing cites. ISO 21920, published in 2021 in three parts, replaced ISO 1302, ISO 4287, ISO 4288, and ISO 13565-2 and -3, which were withdrawn. ASME B46.1 is the US standard. Drawings issued before the change remain valid under the former standards, and new drawings may reference either. This matters more than it sounds: while parameter definitions are largely retained, the calculation method changed for several parameters, so the same physical surface can report a different value depending on which standard the measurement followed. Confirm which standard governs before disputing a finish result.
Ask for the certificate, then verify it independently rather than relying on the document itself. Aerospace certification scope can be checked in the IAQG OASIS database. Nadcap accreditation can be confirmed through the Performance Review Institute's public listing. For any certification, check three things: that it is current, that its scope covers the processes your part requires, and that it covers the facility doing the work rather than a corporate parent or another site. A certificate that is valid but scoped to a different process or location does not apply to your part.
Buyer's Guides
In-depth guides covering the decisions above.
Buyer's Guide
What to decide first, what belongs in the RFQ package, how to run the question period, and how to read the quotes that come back.
Read the guideMore coming
Additional guides are added when there is something genuinely worth saying, not on a schedule. IWS is committed to providing educational content to help you find the right suppliers!
Downloadable Resources
Practical tools you can take into a supplier conversation.
Checklist
Everything a machine shop needs in order to quote accurately, assembled before you send the package. Complete it once and you will get comparable quotes back instead of a spread built on different assumptions.
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