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.

But how would you make a 'traditional split mould', out of fibreglass? If so, how do you make the pattern? Starts to get expensive and approaching the cost of just making an aluminium mould, IMO :-)

As the OP required a nice external finish aluminium is also a good candidate as it polishes easily to a mirror finish without the need for gel coats etc. Once you start to start to add up all the processes, time and materials required to make a traditional pattern and mould, the CNC aluminum mould (no pattern required) gets better and better IMO :-) If the OP requires multiple copies of his item them an aluminium mould is a no brainer as far as I am concerned.