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FAI vs CMM Inspection: What Medical Device Teams Need to Know

Created on 10.27

FAI (First Article Inspection) and CMM (Coordinate Measuring Machine) inspection serve different purposes in medical CNC manufacturing. FAI is an inspection process used to verify that the first manufactured part meets the approved requirements. A CMM is a measuring machine used to check part dimensions and geometric features. A CMM can be used during FAI, but CMM inspection alone is not the same as a complete FAI.

For medical device engineers, purchasing teams, and quality managers, understanding this difference helps define the right inspection plan, request the correct reports, and avoid quality issues before production moves forward.

What Is First Article Inspection (FAI)?

First Article Inspection is a detailed inspection of an initial manufactured part against its approved engineering requirements.

The purpose is to check whether the part has been manufactured according to the drawing, material specification, and other agreed requirements. It also helps identify problems with the manufacturing setup before more parts are produced.

Depending on the project, an FAI may include checks of:

l Dimensions and tolerances on the engineering drawing.

l Hole positions, profiles, threads, and other specified features.

l Material grade and required material documentation.

l Surface finish, edge conditions, and other drawing requirements.

l Special process requirements and related records, where applicable.

The results are documented in an FAI report or other agreed inspection records.

For example, before producing a batch of precision CNC-machined medical components, a manufacturer may inspect the first part to verify that critical dimensions and other specified requirements have been met. If a problem is found, the process can be reviewed and corrected before continuing production.

FAI requirements depend on the customer, product, and project. Buyers should confirm the required inspection scope, report format, and approval process before production begins.

What Is CMM Inspection?

CMM stands for Coordinate Measuring Machine. It is a measuring machine that uses a probe to collect coordinate data from a part and evaluate its dimensions or geometric features.

A CMM is useful for parts with complex shapes, multiple holes, precise locations, and geometric tolerances that may be difficult to check with basic measuring tools.

Depending on the machine, probing method, measurement program, and part geometry, CMM inspection can help measure:

l Distances between features.

l Hole diameters and positions.

l Flatness, perpendicularity, and other geometric characteristics.

l Profiles and complex three-dimensional surfaces.

l Relationships between multiple features.

CMM inspection can produce measurement results that are recorded in a dimensional inspection report.

However, a CMM does not automatically inspect every feature on a part. The measurement plan must identify what needs to be measured, and the part must be set up and measured using an appropriate method.

A CMM also does not replace material verification, visual inspection, surface roughness testing, or other checks that may be required by the drawing or customer specification.

What Is the Difference Between FAI and CMM Inspection?

The main difference is their purpose.

FAI checks the first manufactured part against the agreed requirements. CMM inspection is one method of measuring the part.

FAI defines the inspection activity and the evidence required for the initial part. CMM refers to equipment and a measurement method that can be used to collect dimensional data.

For example, when manufacturing a CNC-machined component with several precision holes and complex surfaces, a supplier may use a CMM to measure those features during FAI. The results can then be included in the FAI documentation.

The same CMM may also be used later for in-process inspection or final dimensional checks, depending on the inspection plan.

Not every FAI must use a CMM. Some features may be measured more appropriately with a micrometer, height gauge, optical measuring equipment, or another suitable instrument. The correct method depends on the drawing, tolerances, geometry, and required measurement accuracy.

Likewise, a CMM report by itself does not prove that every FAI requirement has been completed.

When Should Medical Device Teams Request FAI?

FAI is particularly useful when a new CNC part enters production or when the manufacturing process changes in a way that may affect product conformity.

Consider requesting FAI when:

l A new part is entering production.

l A prototype is moving toward low-volume manufacturing.

l A customer requires first article approval before batch production.

l A manufacturing change requires renewed inspection under the agreed quality procedures.

l A part has complex geometry or critical dimensions that need documented verification.

For example, an engineer may revise a drawing to change a hole position or add a tighter tolerance. The supplier and customer should review whether a new FAI or additional verification is required before the revised part is released.

FAI should not be treated as a universal requirement for every CNC order. The requirement, inspection scope, and approval process should be agreed with the customer.

It is also important to distinguish FAI from ongoing production inspection. An acceptable first part does not eliminate the need for suitable process controls and inspection during subsequent production.

When Is CMM Inspection Especially Useful?

CMM inspection is valuable when the part geometry or tolerance requirements need precise coordinate-based measurement.

For medical CNC components, it may be appropriate for parts with multiple holes, complex profiles, tightly controlled feature positions, or several geometric relationships.

It can also help engineering and quality teams compare measured results with the dimensions and tolerances defined on the drawing.

However, not every dimension requires CMM inspection. For simple features, other measuring instruments may be suitable and more efficient.

The supplier should select an appropriate measurement method based on the characteristics being checked, the specified tolerance, equipment capability, and the agreed inspection plan.

For critical features, buyers should confirm which dimensions will be measured, whether actual measurement values will be reported, and how measurement results will be linked to the relevant part or production batch.

What Should an FAI or CMM Inspection Report Include?

Before production starts, confirm exactly what information the customer expects.

Depending on the project, an FAI report may include the part number, drawing revision, material identification, inspection results, and evidence that the required characteristics have been checked.

A dimensional inspection report may include nominal dimensions, specified tolerances, actual measured values, and acceptance results. Where necessary, it may also identify the measuring equipment or inspection method.

For medical CNC projects, buyers should also clarify whether the reports need to include:

l All dimensions or only selected characteristics.

l Critical dimensions identified by the drawing or inspection plan.

l Part and batch identification for traceability.

l Material certificates or other supporting documentation.

l Customer approval before production continues.

l Final inspection records for the delivered batch.

A clear agreement avoids a common problem: receiving an inspection report that contains measurements but does not cover all the characteristics required by the purchase order.

How Does Marigold Rapid Approach FAI and CMM Inspection?

Marigold Rapid provides CNC machining and custom manufacturing services for prototypes and low-volume production.

Our published Quality Management System describes first article inspection, in-process checks, final inspection, traceability, and dimensional inspection reports. CMM is also listed among our dimensional inspection equipment.

For each project, the required inspection scope should be based on the approved drawing, material requirements, tolerances, order quantity, and customer quality requirements.

When requesting a quote, please provide the latest 2D drawing, a 3D CAD file where available, the required quantity, and any FAI or inspection report requirements. This helps us review the project and confirm the inspection deliverables before production begins.

Visit our CNC Machining Service or contact Marigold Rapid to discuss your requirements and request a quote.

Frequently Asked Questions

Is FAI the same as CMM inspection?

No. FAI is a first-part inspection process, while CMM is a measurement machine. A CMM may be used during FAI, but it does not automatically cover every requirement of a complete FAI.

Can a CMM be used for First Article Inspection?

Yes. A CMM can measure specified dimensions and geometric features during FAI. The inspection plan should also cover other applicable requirements, such as material identification and surface conditions.

Does every medical CNC part require FAI?

No universal rule makes FAI mandatory for every medical CNC part. The requirement depends on customer specifications, project requirements, and applicable quality procedures.

Does CMM inspection guarantee that a part meets every requirement?

No. A CMM checks the features included in its measurement program. Material grade, surface finish, visual defects, cleanliness, and other requirements may need separate verification.

Should I request both an FAI report and a CMM report?

It depends on your quality requirements. If the customer requires an FAI report and detailed dimensional results, confirm whether the CMM measurements will be included in the FAI report or supplied separately. Agree on the required format and inspection scope before production starts.