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. 

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.

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

A lot of people would use a gelcoat during wet lay up rather than a thin coated layer of resin.  Infusion is even more efficient.  You can change how much resin is squeezed out of a wet lay by varying the level of vacuum but you risk having pinholes or dry spots on the surface if you go too high. 


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

It's quite easy to control where the resin flows in infusion. If there is a shorter path available, just leave the flow mesh out of those areas to slow the resin down and allow the other areas to infuse first. It will certainly make a lighter and better part than wet-lay.

I personally would machine and finish the plug in one piece and make the two part mould like it is shown in the easycomposites video with the part line made from a plastic sheet rather than milling two halfes. I feel like this you would get a much smaller/nicer parting line. If you want to seal and polish the two mould halfes separately they will never line up perfectly and the right angle corner will get rounded over which will result in more post work on the final part. There is even a big risk that you will sand through a complete layer of fabric during finishing which is not only bad from a structural point of view, but also esthetically.
Depending on how the moulds line up I would brush on some gel coat in this area so you have some material to sand into without sanding into the fabric.
Cheers!

Got all the materials coming to get going on this project. I have a pretty straight forward idea of how I'll get the plug and then molds done, but i still havent decided exactly how I'll do the lay up. I'm wondering if it might be more easy and controllable to do the 2 halves separately and after they have cured, trim them to fit eachother nicely down the middle. I can make a jig on my cnc that is a negative profile of the center line so the flange of each finished half will sit in this profile while I machine the joint line, basically just removing the flange of each half. The 2 halves will fit together perfectly. I can hold them together on the outside with packing tape while using a strip of fabric on the inside to join them. 
Should this work ok? I'm just worried that it would be difficult to do this whole shape in one shot with a decent seam line in the middle where fabric overlaps. Also I feel that bagging it effectively inside the cone shape with all the needed layers will be difficult. Doing each half separate becomes very simple, just depends how well my joining method works. If the machining of the joint doesn't come out perfect, I figure I can basically lap the 2 halves on a big peice of sand paper on a flat surface to get a nice tight joint between 2 halves. 
Keep in mind I'm a total newb at this so I'm ok with a process that takes more work but is more controllable. Also the mold will be designed in the standard way so I can try it both ways. All in one shot, or 2 separate halves. Not much material in each try so not very expensive. First try will be a single layer of 7.2oz fabric with reinforcment in strategic areas. It will be a pretty flexible flimsy part, but thats what's needed to get it light. Standard fiberglass canopies are usually 2 layers of 5.8oz. Goal is to get similar strength to regular fiberglass canopy but a bit less weight.