Composite mold making questions Options

[TonyAKAVW]

I want to make a diffuser/engine pan for my car, and last night I started gluing foam sheets together to make a mold. My plan is to form the foam into the shape I want and then seal it with body filler, and then primer and polish. I have been reading up on making molds for composite work and most seem to talk about making a copmosite piece for the mold rather than what I am planning. If I make my mold as described will my composite part rip the mold apart when I seperate the two? (assuming I use a PVA mold release film).

Also, if I make the part with carbon fiber, how do I finish the edges of the piece when I'm done?

I would like to vacuum bag this part because the part will be visible from the top and the bottom... Can I get away not bagging it and get a decent finish? (I'm not super concerned that it has a perfect surface really).

-Tony

Finished part will look something like this...

With the long straight edge meeting up against the firewall and the two tunnels exiting right under the bumper.

[JPB]

Its not to hard to do Tony. If your mould is smooth and blemish free, assuming the foam part you are using is the mould and not a plug, it will be easy to get a good finish. What I do is lay up just resin or epoxy like three times for a good build up to sand later to a glass finish. It should get some acrilic clear on it to keep them UV rays off so it will get a good grit sanding before that also. For me, the hardest thing is to get the CF as thin as possible and as strong as it needs to be. The best time to trim anything is when the stuff gets geled and not yet hardened since you can cut it with a razor knife but you can use a grinder to get the shape you want when its completely hard.