Tolerances in composite parts and how they are measured.
A composite part does not behave like a metal one: curing distorts it slightly, thickness depends on the laminate and some surfaces cannot be machined. That is why tolerances are defined differently, and measuring before and after lay-up is the only way to guarantee them.
Carbodynamic engineering team · Published on
What makes composite dimensions vary
- Springback: on demolding, angles tend to close slightly due to resin shrinkage.
- Thickness: depends on the number of plies, compaction and the process; the mold-side face is accurate, the other less so (except in RTM).
- Mold expansion: an aluminum mold grows with temperature more than the carbon part does.
- Trimming and drilling: edge and hole dimensions depend on post-cure machining.
How we control it
Our rule is to measure twice. We measure the mold before lay-up, to know the starting point is correct, and we measure the finished part with a FARO arm, laser tracker or CMM in a climate-controlled room.
We deliver a report with the deviations from the CAD. If needed, we compensate the mold to correct springback on subsequent parts.
Tips for specifying tolerances
- Apply tight tolerances only to what is functional: joint areas, mounting holes, bearing surfaces.
- State which face is the datum (usually the mold side).
- For edges and holes, think in machining tolerances; for freeform shapes, in profile tolerance.
- Ask us before you finalize the drawing: we will tell you what is reasonable for each process.
CMM inspection
CMMs in a climate-controlled room and measurement reports.
Technologies3D scanning and reverse engineering
From physical part to CAD model, plus part-to-CAD comparison.
CarbodynamicMetrology
3D scanning, FARO dimensional inspection and CMMs: sales, retrofit, maintenance and ENAC calibration, as Téciman’s eastern Spain hub. Ibi (Alicante), Spain.
Technical articlesCMM, FARO arm or 3D scanner
Which measurement method to choose by accuracy, size and location.
Send us your drawing or 3D model, and we’ll bring it to life.
We study your project with the same care you put into designing it, then send you a clear proposal covering process, lead time and price. Only have the physical part? We’ll scan it and take it from there.
What customers ask us most.
Can metal-like tolerances be achieved on a carbon fiber part?
In areas machined after curing, yes, machining tolerances can be achieved. On laminated surfaces, the tolerance depends on the mold and the process.
How do you measure a large composite part?
With a FARO arm or laser tracker on a support fixture, comparing the point cloud against the CAD.
Do you provide an inspection report?
Yes, with the dimensions, the tolerances and the deviations found.