CNC Machining Inspection Checklist and CMM Report: What to Require and How to Read It

Rule Out Reports That Do Not Tie Results to the Drawing

A long printout is not necessarily a complete report²⁴. The report is only evidence if each result connects to the correct drawing feature, revision, inspected part, and acceptance decision^23,24.

Two independent publishers agree on the content blocks a complete report must carry, including report identity, part traceability, drawing basis, equipment and probe configuration, datum alignment, and nominal/actual/deviation/PASS-FAIL results^23,24. Calibration, environmental, or uncertainty information is included when contractually required, so the buyer must state that requirement up front^23,24.

Neither source establishes a mandatory report template, a required number of points per feature, or a specific software/version disclosure obligation^23,24.

• ✓Each result ties to a drawing feature number and drawing revision
• ✓Each result ties to the inspected part, serial, lot, or sample ID
• ✓Report identity: report number, inspection date, revision, approval status
• ✓Drawing basis: drawing number, revision, units, general tolerances, GD&T standard
• ✓Nominal value, tolerance limits, actual value, deviation, and PASS/FAIL per feature
• ✓Datum alignment: primary, secondary, tertiary datums and restraint condition
• ✓Equipment and probe configuration identified

Which Drawing Callouts the Checklist Must Force the Supplier to Measure

The feature control frame fixes the tolerance zone and the datum precedence the CMM must evaluate, and the report must record the result per feature^9,17,23.

A feature control frame contains, in fixed sequence, the geometric characteristic symbol, the tolerance value (with a diameter symbol for cylindrical zones), datum references in order of precedence, and optional material condition modifiers⁹. Basic dimensions are boxed, untoleranced values that define the theoretically exact location of a feature relative to specified datums⁹.

Material condition modifiers applied to the tolerance value or datum reference allow additional positional tolerance as the feature size departs from its specified limit, per bonus tolerance principles in ASME Y14.5⁹.

The checklist should therefore list every feature control frame, its datum sequence, its basic dimensions, and any MMC/LMC modifier, so no GD&T requirement is silently skipped^9,17,23.

Confirm the Report Carries the Required Content Blocks Before Accepting It

Two independent publishers agree on the same content blocks, and calibration or environmental information is included when the contract requires it, so the buyer must state that requirement up front^23,24.

A CMM records discrete points or traces continuous paths with a tactile stylus along three axes and is suited to datum-based GD&T, interrelated 3D geometry, and precision characteristics; it requires part restraint, probe access, programming, and stable surroundings¹¹.

• ✓Report identity: number, date, revision, approval
• ✓Part traceability: part name, number, serial, lot, or sample ID
• ✓Drawing basis: number, revision, units, general tolerances, GD&T standard
• ✓Material and finish: grade, temper, and whether inspection was before or after finishing
• ✓Inspection scope: feature list, inspected quantity, sample plan, characteristics not included
• ✓Measurement equipment: equipment ID, CMM type, probe or sensor configuration
• ✓Equipment status: calibration or performance-verification status and due date when contractually required

Choose the Measurement Method per Characteristic from the Tolerance

Method is picked from the tolerance, and tighter tolerances increase inspection time and scrap rate, which feeds the per-piece and fixed inspection cost build-up^32,33. CMM is suited to datum-based GD&T and interrelated 3D geometry, while hand tools are limited in coverage of multi-axis relationships and advanced GD&T¹¹.

A go/no-go gauge produces only attribute acceptance or rejection and reveals no actual deviation¹¹. No source establishes which method is mandatory for a given tolerance or feature type¹¹.

Decide Whether the Order Needs a First Article Inspection

FAI per AS9102 verifies that the production process can consistently produce parts meeting every design requirement, includes complete dimensional reports, material certifications, and inspection of every characteristic on the drawing, and is required on the first production run and whenever the process changes¹⁹.

FAI requires a ballooned drawing with sequential numbered circles on every dimension and feature, a measurement plan specifying instrument and method per characteristic, and 100% dimensional measurement recording actual values rather than pass/fail stamps²⁷.

The sources do not establish whether FAI is required for non-aerospace CNC work or what a standard FAI report must contain beyond dimensional reports and material certifications^4,19,30.

Some suppliers present FAI as a custom, additional-cost option while aerospace/defense contexts treat it as required, and the difference tracks the applicable quality regime rather than contradicting the requirement^4,19,30.

Settle Whether Inspection Is Inside the Piece Price or Billed Separately

Inspection cost should be built from inputs: count of characteristics to measure, method per characteristic chosen from the tolerance, per-piece measuring time at the burdened rate, per-lot fixed costs (CMM programming, fixturing, FAI), and documentation hours, with fixed costs spread over order quantity³².

Fixed inspection costs dominate at low quantity and nearly vanish at high quantity³². One supplier includes a standard dimensional inspection report free of charge for all CNC parts while charging extra for FAI, PPAP, and APQP⁴.

Quotes should be checked for whether deburring, tapping, and inspection are included and whether there is a one-time setup charge³⁴. No source establishes a standard market practice for whether inspection is included in piece price^4,32,34.

Require the Documentation Package That Travels with the Parts

Material certification traceability requires a documented chain from raw material mill certificate to finished part, with each piece traceable to its heat lot, chemistry analysis, and mechanical test data¹⁹. AS9100 requires complete material traceability with 100% documentation retention from raw material to finished part for a minimum of 10 years²⁹.

AS9100D includes clauses addressing product safety, prevention of counterfeit parts, configuration management, and enhanced supplier management⁶. Buyers should request inspection reports, equipment lists, calibration practices, process control plans, first article reports, material certificates, in-process inspection records, and gauge control records, and should check tight-tolerance claims against actual measured results²⁸.

The sources do not establish whether AS9100, IATF 16949, or ISO 13485 is mandatory for a given part^6,29.

Where the Sources Give Different Figures for the Same Inspection Item

The sources disagree on how inspection cost is treated and what FAI adds, so the buyer should ask the supplier to resolve the figures rather than averaging them^4,32,33. The figures below are single-source observations, not industry-standard values^4,32,33.

What the sources do not establish

• No source provides AQL values, sample-size tables, or acceptance criteria for sampling plans.
• No source provides test uncertainty ratio or gauge R&R acceptance thresholds.
• No source provides calibration intervals, NIST/ISO 17025 traceability specifics, or temperature compensation procedures.
• No source provides Cpk/Ppk targets or PFMEA/control plan content requirements.
• No source provides a required number of points per feature or CMM software/version disclosure rules.
• No source provides NCR form content, CoC/CoA templates, or rework/reinspection policy detail.
• No source provides inspection labor rates, CMM programming time benchmarks, or FAI turnaround times beyond one illustrative example.
• No source provides surface finish (Ra) acceptance criteria or measurement methods for surface finish verification.
• No source provides a complete checklist template combining GD&T, dimensional, surface finish, documentation, and sampling items.
• No source establishes whether FAI is required for non-aerospace CNC work or what a standard FAI report must contain beyond dimensional reports and material certifications.
• No source establishes a standard market practice for whether inspection is included in piece price.
• No source establishes whether AS9100, IATF 16949, or ISO 13485 is mandatory for a given part.