Also for that size, if you are going to the hassle of vacuum bagging it, go for infusion.  No gelcoat needed then so you should have a slightly lighter part.  As its not too big, just envelope bag the whole mould.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Your first plan is solid, it's exactly what I would do. Personally I would mill it out of tooling board rather than MDF or foam, as MDF doesnt machine very nicely (not compared to tooling board anyway) and neither MDF nor foam are very stable. Not super important for a plug, but tooling board is just amazing stuff to work with so that would be my choice.

You could also consider using the tooling board to mill a female mould directly. I agree it isn't quite as easy, but it can be done and could save some time and cost if you only need one or two of these things.

I already posted about my carbon fiber helicopter boom, for that I decided I'll bite the bullet and do alloy molds. 
I also need a carbon fiber helicopter canopy. Similar shape to a football but a bit bigger and open at the back, I'll attach a pic of one. It will have pretty thin wall thickness, generally they are about a half mm, maybe .6 or .7. So only a couple layers of weave. 
I will be making my own design on fusion 360 and milling the plug on my cnc. The process that makes the most sense to me is milling each plug half (mold will be split down the middle lengthwise, right and left half) out of mdf or foam, spraying it with layers of duratec primer, sand and polish, then attach each plug half to a flat sheet of melamine or some other rigid plastic to create base for mold flanges and proceed to make fiberglass mold halves from that. I would prefer to skip the plug stage and go straight to milling the molds, but it just doesn't seem to work out as well as making fiberglass molds from a plug.  From the female molds I will vacuum bag a carbon fiber wet lay up. 
does this sound like a good plan or is there an easier/better way considering I have a cnc? Another variation would be attaching the 2 plug halves together to make a complete plug before applying duratec,  then split into 2 molds using the method shown in the air box video, but i feel that it will be less work to just attach the 2 halves to flat sheets for making the molds, just need to make sure both sheets are perfectly flat planes.