I have years of working with fiber glass chop (unfortunuately as chop is the worst substance known to man!). Recently have been working on a project where I have need for a lightweight iregular shaped tube, thought maybe carbon would be a good choice. It doesn't need to be exceptionally strong, or exceptionally pretty as it'll be painted. Reasonable strength and lightweight are the goals. (The picture attached is just a mockup, I haven't looked for unmachinable features, proper tangency or areas I may need draft)

1. See pic. Is there any reason a shape like this can not be made using a positive pressure inflatable bladder and two female mold (mould?) halves? Seems I can lay up both havles, alternate the wet-seal top and bottom, insert the bladder, and bake.

2. I see a lot of people (airplane builders mostly) use custom shaped bladders made from garbage bags. Bike builders often use bike tubes. Some people recommend party balloons. Latex, silicon, etc. I've been reading that 10-20psi should be plenty... Do I need a custom shaped balloon? Benifit from one? Get by fine without?

3. Pre-Preg sure does seem a lot less messy. Is there any reason that would not be ideal for this?

4. I can easily cut the female moulds on a CNC, but it's router so I'm limited to wood, ren plank, foams, plastics, etc. Anything but metal. Issue in terms of positive pressure or curing?

5. Not shown in the picture that I have four .75" x 4" aluminum strips that need to be placed on the top/sides/bottom. I haven't looked into how to attach these yet. Molding in seems like it would be ideal as the molds are CNC cut I can assure excellent placement. I saw a lot of warnings about combining aluminum and carbon but mostly when there is electricity evolved. This tube is part of an aluminum and steel assembly that is far removed from electricity. Is corrosion still a concern?

6. How concerned should I be that I've never worked with carbon and am considering this project?

Any direction would be more than appreciated!

Re-post the image.. I cannot see it...

http://s2.postimg.org/umih124tz/Carbon1.png

Sorry, here it is as a link, should work regadless of forum settings or mobile browser.

I should note that I know there is not radius at the keyhole end, just a mockup

If you can get resin block cnc cut then it would be quite easy...

Pre-preg is the best option. You dont need positive pressure then you can just use vaccum to get 14psi of pressure. If you are careful you can do the whole thing without having to do two halves and then bonding it together....

The idea was to do two mold halves and combine while wet, then inflate bag.

Part of the reason I'd like positive pressure is I don't have a vac pump that would be ideal for carbon.

The down side to positive pressure is you need to contain the bladder to keep the pressure into the mould. Using a vacuum means the bag can pull down and no containment is needed.

I don't want to side track my own thread but...

It certainly can be made with a bladder mold if it is closed off like morepower said.  I think it would be a million times easier to use prepreg and vacuum pump.  If you dont want to fork over a lot of money for a vacuum pump.  You could use a refrigerator compressor for 20-30 bucks but then again you are talking about cnc parts so I would just pay for a $50 pump (don't know where you are located but here is a link to 3cfm unit).  Plus by having a vacuum pump this will allow you to explore rtm and vacuum bagging if you wanted in the future. You will have higher cost of materials per part with prepreg but it will be a lot easier.  But there are many ways to skin a cat.  Good luck in which ever method you choose.  

Even simpler is to use a solid silicone intensifier or core.

So you would need to cast the silicone less the skin thickness in your mould using CSM or sheet wax.

Silicone expands a lot with heat and makes good pressure so no need for bags, bladders, pumps or compressors but you will need an oven for pre preg.

You may need to form some kind of extension to the silicone so you can grip it to remove. If you wanted you could also cast it with a metal tube down the centre simply to reduce the silicone since it is expensive. Maybe the tube could be withdrawn and then the silicone would also release/remove even easier?

I have made small yacht parts like this and it works great.