| Quality Management |
A documented quality system with controlled procedures, nonconformance handling, and corrective actions. |
A current ISO 9001 certificate issued by an accredited certification body, with a clearly defined scope covering machining or manufacturing. |
ISO 9001 supports process consistency, but certification alone does not guarantee that every part will meet a specific tolerance. |
Can you provide the certificate scope, expiry date, and sample quality records? |
Important for repeatability, supplier accountability, and prototype-to-production transition. |
| Drawing Interpretation |
The supplier confirms units, datums, geometric tolerances, surface-finish symbols, and revision level before machining. |
A formal design-for-manufacturing review identifies ambiguous dimensions, impossible tolerances, and inspection datums before quotation. |
ASME Y14.5 or ISO GPS practices may be used for dimensioning and tolerancing; the governing system should be stated on the drawing. |
Which drawing standard will govern interpretation, and how are conflicting notes resolved? |
Clear interpretation reduces disputes, rework, and unexpected inspection failures. |
| General Dimensional Tolerance |
The quotation states a default tolerance only where the drawing does not define a value. |
The supplier separates standard machining capability from guaranteed tolerances for individual critical features. |
ISO 2768 may be used for general tolerances when explicitly referenced; it should not replace specific feature tolerances. |
What default tolerance applies to this quotation, and which dimensions require a separate capability review? |
Avoid suppliers that advertise one universal tolerance for every material, size, and geometry. |
| Tight Feature Tolerance |
The supplier reviews tolerance, feature size, material, tool access, thermal effects, and inspection method together. |
Documented process capability data, trial results, or a first-article measurement demonstrates that the required tolerance is achievable. |
For many CNC prototypes, approximately ±0.05 mm is commonly quoted; approximately ±0.01–0.02 mm normally requires special process control and verification. Actual capability varies. |
Can you provide measured results for similar features and define the measurement uncertainty? |
Choose based on demonstrated capability, not a generic website tolerance claim. |
| Geometric Tolerances |
The supplier can inspect position, flatness, perpendicularity, parallelism, profile, and runout when specified. |
The inspection plan identifies datums, measurement points, alignment method, and acceptance criteria for each critical characteristic. |
ASME Y14.5 and ISO GPS standards provide established frameworks for geometric product specification and verification. |
How will datum alignment and feature location be established during inspection? |
Essential for mating parts, shafts, bearing seats, sealing surfaces, and assemblies. |
| Inspection Equipment |
Calibrated calipers, micrometers, height gauges, thread gauges, pin gauges, and surface-finish instruments appropriate to the drawing. |
A calibrated CMM, optical measuring system, or vision system is used for complex profiles, true position, and multi-axis features. |
ISO/IEC 17025 is relevant to the competence of calibration and testing laboratories; equipment resolution is not the same as measurement accuracy. |
Which instruments will inspect my critical features, and can you provide calibration records? |
The inspection method should be capable of resolving the required tolerance with suitable uncertainty. |
| Calibration Control |
Inspection equipment is uniquely identified, periodically calibrated, and protected from damage or misuse. |
Calibration is traceable to national or international measurement standards, with environmental conditions and out-of-tolerance actions documented. |
A traceable calibration system supports confidence in measurement results; calibration intervals should be risk-based and documented. |
Are calibration certificates available for the instruments used on this order? |
Particularly important when tolerances are close to the measurement system’s practical capability. |
| Inspection Documentation |
A basic dimensional report lists measured values for agreed critical dimensions and identifies the inspected part. |
A ballooned drawing, complete characteristic report, inspection equipment identification, actual values, and pass/fail results are included. |
A report should follow the drawing revision and agreed acceptance criteria; the format is normally defined contractually. |
Will the report show actual measurements or only a statement of conformity? |
Actual data is more useful for engineering decisions and future process improvement. |
| First Article Inspection |
The first completed part is inspected before the remaining quantity is released, when the project risk justifies it. |
A complete first-article report verifies every drawing characteristic, material, finish, special process, and revision-controlled requirement. |
AS9102 is commonly used for aerospace first-article reporting when contractually required; it is not automatically required for every prototype. |
Can you perform a first-article inspection before producing the remaining parts? |
Recommended for complex parts, expensive materials, tight tolerances, or safety-related applications. |
| Material Verification |
The material grade, condition, and quantity match the drawing or purchase order. |
A material certificate records the specification, heat or lot number, supplier, and traceability from raw stock to finished parts. |
Material certificates should identify the applicable material specification; additional chemical or mechanical testing may be required for critical applications. |
Can you provide material certificates and maintain lot traceability through production? |
Do not rely on visual appearance alone to verify alloy, hardness, or temper. |
| Surface Finish |
The drawing specifies the required roughness, coating, deburring, and cosmetic acceptance criteria. |
Surface roughness is measured with a calibrated instrument, while visual standards or approved samples control cosmetic requirements. |
Ra is commonly reported in micrometres; typical milled surfaces may be approximately Ra 1.6–3.2 µm, depending on tooling, material, and parameters. |
How will roughness and cosmetic defects be measured and accepted? |
Specify measurable limits instead of using vague terms such as “smooth” or “high quality.” |
| Process Control |
The supplier documents setup instructions, tool changes, inspection frequency, and handling requirements. |
In-process checks, statistical monitoring, documented work instructions, and controlled revision records are used for repeat orders. |
Statistical process control can monitor variation, but control limits should be based on actual process data rather than assumed capability. |
How do you detect tool wear, thermal drift, and dimensional variation during a batch? |
Strong process control matters more as quantity, tolerance, and functional risk increase. |
| Nonconformance Handling |
Nonconforming parts are identified, segregated, and reported before shipment. |
The supplier provides root-cause analysis, corrective-action records, concession approval, and replacement or rework control. |
A documented corrective-action process is consistent with an effective quality management system. |
What happens if a critical dimension is out of tolerance, and who approves any deviation? |
Choose a supplier with transparent escalation rather than one that quietly ships questionable parts. |
