A 3D printed part that looks correct is not necessarily correct. Surface quality, colour, and absence of obvious defects are visible — dimensional accuracy is not. This is why every manufacturing facility needs a systematic measurement programme, and why customers ordering precision parts should understand what they are (and are not) receiving when they order from a supplier.
Why 3D Printed Parts Need Specific Inspection Approaches
Machined parts are typically inspected at critical features (bore diameters, datum surfaces, thread fit). 3D printed parts have additional failure modes: dimensional variation due to thermal shrinkage, layer delamination creating subsurface voids, support witness marks affecting surface function, and warping due to residual stress. A complete inspection programme addresses all of these, not just the dimensional callouts on the drawing.
Calibrated Calipers and Micrometers — The Baseline
For commercial FDM and SLA parts with tolerances ≥±0.2 mm, calibrated digital calipers (resolution 0.01 mm, calibrated annually against NIST-traceable standards) provide sufficient measurement capability. Layer X uses calibrated Mitutoyo instruments across all production stations. Caliper measurement is appropriate for: external dimensions of parts, hole diameters above 5 mm, wall thickness checks, and length/width/height envelope verification.
Limitation: calipers cannot measure form (flatness, roundness, cylindricity) or position of features relative to datums. For those requirements, CMM is required.
CMM (Coordinate Measuring Machine) Inspection
CMM uses a touch probe traversing a precision granite table under CNC control to measure 3D coordinates of surface points to ±0.002 mm. CMM programs are developed from the customer CAD file or drawing, defining datum reference frames and measurement points for every toleranced feature.
At Layer X, CMM inspection is standard for: AS9100 aerospace orders (all features on drawing), ISO 13485 medical orders (all functional surfaces), any part with GD&T callouts (position, perpendicularity, flatness), and any dimension toleranced below ±0.1 mm. CMM reports are issued in PDF with a tabular comparison of nominal vs actual for every measurement point.
Structured Light 3D Scanning
For complex organic geometries (topology-optimised brackets, patient-specific medical parts, sculptural architectural models) where a CMM cannot reach all surfaces, structured light scanning captures the complete part surface as a point cloud at 0.02 mm resolution. The scanned geometry is compared to the CAD nominal in inspection software (GOM Inspect), generating a colour deviation map that immediately visualises where parts are within and outside tolerance.
Structured light scanning is used at Layer X for: topology-optimised aerospace parts, SLA surgical guides (where all bone-contact surfaces must be verified), and any part with complex curved surfaces where CMM accessibility is limited.
Go/No-Go Gauges for Production
For high-volume inspection of a single critical feature (bore diameter, thread fit, slot width), custom 3D printed or machined go/no-go gauges provide 100% rapid inspection without operator measurement fatigue. Layer X produces gauge sets for customers with production volumes above 200 pieces where the gauge cost amortises quickly against labour savings.
Inspection Levels: What You Can Order
Standard (no added cost): Visual inspection + dimensional spot check of 3 key features with calibrated calipers. Suitable for prototypes and non-critical commercial parts.
Statistical sampling (AQL): 5% sample with full dimensional report per sampled unit. Added ₹50–150/part depending on complexity. Suitable for production batches.
100% inspection: Every part measured at all critical features. Required for AS9100 and ISO 13485 orders; available on request for commercial orders. Quoted on a case-by-case basis.
Full CMM report: GD&T compliance report against customer drawing, PDF issued per part serial number. Required for aerospace FAI and medical DHR. Quoted per part number.