Hi
I need to make 50 cm long carbon fiber octagonal pipe 50mm flat-flat with wall thickness of 2mm, outside surface quality is important. Im looking for ideas how to make it. Currently the best solution i came with is to do vertical vacuum infusion with heat formed pvc pipe as outside mold. If you have any ideas, guidance please share.

Aluminium moulds and bladders will likely be quite an expensive way of doing it.  Pre-preg is still a good option though but make the mould traditionally as a split mould, then basically follow the process as in this video:  Laminating and Vacuum Bagging a Carbon Fibre Tube Using a Split Mould

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant