I want to have a go at making some carbon trumpets for my TBs. The requirement is that should have excellent finish inside ( obviously for gas flow ) but also outside as they will be visible. In the absense of production moulds two approaches suggest themselves:
1) Make male plug to ensure good inside finish and vacuum bag the outside to give best consolidation/finish to the outside
Or
2) Make a female plug and use an inflated bladder ( a section of mountain bike inner tube complete with valve suggests itself ) to consolidate the inner surface.
I guess either approach may require some flow coating and hand finishing . Anyone done this? If so perhaps there is a better way. ( Hope Clairetoo reads this! )

Give Clairetoo a U2U, I seem to remember she made some excellent ones.

Vac bagging still doesnt give an amazing surface finish, and both methods you speak of use the same technique in opposite - I would use the male plug, as you do really want a nice surface finish on the inside. The surface finish on the outside will certainly be tolerable, just not nice shiny weave...
It is possible to get good finish on both sides but involves RTM (resin transfer moulding) or similar ie a two part mould - and as far as i know very hard if not impossible to do at our level - unless you have the facilities to machine male and female moulds and resin injection equipment??

The finish is like this with vac bagging;

http://www.reverie.ltd.uk/product_detail.php?part_code=R01SE0433

Its moulded outside, bagged inside

edit, sorry just reread OP, you dont have moulding available, so yes, male buck inside, bag outside and accept the finish as it comes :/

[Edited on 25/7/11 by hellbent345]

or like this http://www.google.co.uk/imgres?q=carbon+trumpets&um=1&hl=en&sa=N&biw=1440&bih=719&tbm=isch&tbnid=0kaZJXSPfQRD6M:& imgrefurl=http://qedmotorsport.co.uk/qed-shop/view-all-products-in-shop%253Fkeyword1%253Dcarbon%252520fibre%252520trumpets&docid=adbU9O1n1tCHlM&am p;w=800&h=600&ei=T9wtTpPkGsiZ8QOV9pT_Cw&zoom=1&iact=rc&dur=341&page=1&tbnh=136&tbnw=186&start=0&ndsp=24&ve d=1t:429,r:9,s:0&tx=67&ty=71

Matched tooling isn't too hard at home... If you can make an accurate male plug, you can take the next steps too...

Look for sheet wax - it is frequently used in mould building. The idea is, you make the male plug, then layup the sheet wax with the same thickness as the laminate you intend to use. It comes in various thicknesses, right down to 0.25mm (although the very thin wax is a PITA to use!)... Build up you wax part on the plug (you can shape and shave the wax as needed). Once down, Build your outer mould parts (depending upon shape you may get away with making it from one piece, and demoulding from one end).

When complete, open it up, and clean the wax off (acetone will dissolve the last traces). Now you have matched tooling for your trumpets, with a known thickness cavity. Now just build your trumpets... Voila!