| Machine Configuration | Number of controlled axes and simultaneous machining capability | 3-axis equipment is suitable for prismatic parts; 4-axis and 5-axis machining is preferable for complex geometries, undercuts, and reduced setup count. | More axes can reduce repositioning, setup error, and accumulated datum variation. | High |
| Work Envelope | Maximum X, Y, and Z travel, table size, part weight, and fixture clearance | The machine envelope should exceed the finished part size by approximately 20–30% in each relevant direction, while allowing tool access and workholding. | A nominally large machine may still be unsuitable if the tool, fixture, or rotary unit limits usable space. | High |
| Spindle Capability | Spindle speed, power, torque, taper, and cooling method | High-speed spindles support small tools and aluminum; higher torque and rigid tooling are more important for steel, stainless steel, and titanium. | Matching spindle characteristics to the material improves tool life, surface finish, and process stability. | High |
| Positioning Accuracy | Published accuracy and repeatability data, preferably measured under a recognized test method | Request documented machine-test results rather than relying only on a general specification. ISO 230-2 is a recognized reference for machine-tool positioning tests. | Repeatability and volumetric performance directly affect hole locations, mating features, and multi-face alignment. | High |
| Tolerance Capability | Ability to manufacture the drawing’s general and critical tolerances | For many standard milled parts, ±0. daw? Replace. Typical commercial capability is about ±0.10 mm; tighter tolerances such as ±0.025 mm require controlled processes, suitable machines, and inspection evidence. | Tolerance capability depends on material, feature size, geometry, thermal conditions, and measurement method—not only machine resolution. | High |
| CAM and Process Planning | CAM simulation, collision checking, toolpath optimization, and revision control | The supplier should be able to provide a documented process plan, simulate complex toolpaths, and maintain controlled revisions of CAD, CAM, and drawing files. | Digital process control reduces collisions, wrong-revision production, excessive tool engagement, and unnecessary cycle time. | High |
| Automation | Tool presetting, probing, pallet systems, bar-code or traveler control, and unattended machining controls | For repeat production, in-machine probing and tool-life monitoring are valuable. Automation should be supported by documented alarm handling and verification procedures. | Automation can improve repeatability and throughput, but it does not replace first-article inspection or process validation. | Medium–High |
| Material Control | Material identification, certificates, heat or lot traceability, and incoming inspection | Require material certificates when specified, including grade, heat or lot number, and relevant mechanical or chemical information. | Traceability helps prevent material substitution and supports investigation of dimensional or performance failures. | High |
| Workholding and Fixturing | Fixture design, datum strategy, soft jaws, modular tooling, and repeatable loading | The supplier should explain how datums are established and how thin walls, deep cavities, and distortion-prone parts are supported. | A strong machine cannot compensate for unstable workholding, incorrect datums, or excessive clamping force. | High |
| First-Article Inspection | Inspection plan, ballooned drawing, critical-feature records, and sample approval | For new or revised parts, require a first-article report covering all drawing characteristics or an agreed list of critical features before volume production. | First-article inspection confirms that the process can produce compliant parts before production quantities increase. | High |
| Measurement Equipment | Calibrated calipers, micrometers, height gauges, gauges, optical systems, and CMM access | Inspection equipment should be appropriate to the tolerance. Calibration records should be current and traceable to recognized national or international standards. | Measurement uncertainty must be sufficiently smaller than the tolerance being verified. | High |
| Quality Management | Documented procedures, nonconformance control, corrective action, and internal audits | ISO 9001 certification is a useful baseline for a documented quality management system, but certification should be supported by actual inspection and corrective-action records. | A quality certificate alone does not prove that every process or project will meet the required specification. | High |
| Geometric Dimensioning | Understanding and application of GD&T, datum schemes, position, profile, flatness, and runout | The supplier should interpret ASME Y14.5 or the applicable drawing standard consistently and identify ambiguous or conflicting requirements before machining. | Correct GD&T interpretation protects functional relationships that ordinary ± dimensions may not fully define. | High |
| Surface Finish | Ability to achieve specified roughness and cosmetic requirements | Common machined finishes are often specified using Ra values; confirm the measurement direction, inspection method, and whether secondary finishing is included. | Surface finish depends on tooling, feed rate, vibration, material, toolpath, and post-processing—not just the programmed step-over. | High |
| Process Validation | Capability studies, control plans, sampling frequency, and statistical monitoring | For repeat production, ask for evidence of process monitoring and agreed reaction plans for out-of-control or nonconforming conditions. | Validated processes reduce variation across batches and make quality performance more predictable. | High |
| Lead Time and Capacity | Quoted lead time, available machine hours, material procurement, and bottleneck operations | Request a schedule that separates engineering, material purchasing, machining, inspection, finishing, and shipping. Confirm capacity for repeat orders. | A low machining price is not useful if inspection, finishing, or constrained equipment creates schedule risk. | High |
| Finishing and Secondary Operations | Deburring, anodizing, plating, heat treatment, passivation, painting, and marking controls | Define the finishing specification, thickness or hardness requirement where applicable, appearance criteria, and certificate requirements before quotation. | Secondary operations can change dimensions, corrosion resistance, hardness, and cosmetic acceptance. | High |
| Documentation Package | Inspection report, material certificate, finishing certificate, deviation approval, and packing record | Agree on the required documentation before production. Records should identify the part revision, quantity inspected, results, and acceptance status. | Complete records simplify receiving inspection, audits, warranty investigations, and regulated-project compliance. | Medium–High |
| Communication and Engineering Support | Design-for-manufacturing feedback, response time, change management, and technical clarification | Prefer suppliers that identify inaccessible features, unrealistic tolerances, sharp internal corners, thin walls, and avoidable setups before production. | Early engineering feedback can reduce cost, lead time, scrap, and late drawing changes. | High |
| Supplier Qualification | Sample parts, references, audit access, equipment list, and documented performance history | Use a sample or pilot order to verify dimensional results, communication, packaging, documentation, and on-time delivery before approving larger volumes. | Actual evidence from a representative part is more reliable than a capability claim made without supporting records. | High |
