Carbon Fibre Parts: Layup, Curing and What Tolerances to Expect

Carbon fibre parts are not a single product category. A prepreg autoclave part and a wet-layup cosmetic cover share a name and nothing else.

Prepress and layup. Prepreg carbon is laid by hand or by automated tape laying, then cured under pressure. Fibre orientation determines stiffness: 0° for tensile strength, ±45° for torsion, 90° for hoop strength. The layup schedule is the design.

Curing. Autoclave curing gives the lowest void content and the best surface finish. Out-of-autoclave prepreg and resin infusion are cheaper but leave more voids and require thicker clear coat.

Tolerances. Expect ±0.2 mm on machined interfaces and ±0.5 mm on cosmetic surfaces. Tighter than that needs CNC finishing after cure, which adds cost quickly.

Finish. Clear coat over visible weave is cosmetic; a painted part hides weave defects. UV stability matters outdoors — cheap resin yellows within two years.

Testing. For structural parts, ask for a sample test report: fibre volume fraction, void content and a three-point bend result. A supplier who cannot provide one is selling appearance, not engineering.