I've made some parts that were under vacuum and cured for 24h.  They were then post cured in the moulds for 8 hours at 60 deg C.  I've pulled them, trimmed them and lacquered them and I've found a slight movement in the moulding.  Its a scoop and its 'opened out on its edges.  Any ideas whats caused it and how I can stop it?  I can flex the moulding back to how it should be to bond the grilles in (about 4-5mm out)  but I'd like to be able to stop it in the future.

Hi,

• Dissimilar materials - e.g. backing carbon with glass, this often creates a very noticable distortion especially when cured above ambient. it creates internal stresses in the part that in turn 'pull' it around.
  
• Imbalanced laminate - e.g. 1 ply 200g, 1ply 650, 2plys 200g , every weight and style of fibre performs differently even when it's all the same fibre type (e.g. carbon) this will have a similar effect to using dissimilar materials but less pronounced.
  
• Not using epoxy resin - resins such as polyester shrink alot more than epoxies and will 'pull' the part poor quality epoxies can do the same thing.
  
• Uneven curing - if the part is not cured evenly (commonly caused by uneven heating) this too will tend to distort the part
  
• Fibre orientation - rarely causes distortion but aim to keep a balance where possible

Guilty of any of the above? if so address that, if not we'll keep hunting until we find the problem!

Paul Statham
Easy Composites / Carbon Mods - Technical