Following on from my previous thread in "Pattern and plugmaking" http://www.talkcomposites.com/623/Pattern-Making-and-CAD,-need-advice 

in which you can see the design and pattern making of this spoiler



My plug is now nearly ready



I'm now thinking about how to make the mould, i'm considering making a 2 part split mould as illustrated cross section below, i haven't done this before so please add your comments on how you think it would work out or how i can do it better.

what would be the best material to use for the barriers?

Nice work you are doing.

There are a number of ways to make your flanges. I have used plasticine, wood and metal sheets at various times.

When I watched the Easy Composites video of the car hood molding, I decided to try that. It worked great and was far faster than my other methods.

The sign board is cheap, flexible and the epoxy did not stick to it. Where the sign board meets the plug surface I tried the yellow wax EC sells and it is fantastically accurate. I used the hot glue gun method they show to glue the pieces together and that worked well also.(before I tried I was sure that it wouldn't stick. but it does)

One thing I would recommend is that you continue the lips where you intend to cut, oversized. So you have a full thickness to cut through of uniform laminate thickness. If that makes sense. You know how the edges of your molded part tend to taper in thickness at the outer edges of your part. 

Hope this helps.

Fred