how do i make a mould of bonnet and have a nice flange around the edge? im going to lay some resin and chopped fibre over my waxed bonnet but need a flange? do i tape cardboard or wood around the edges to give me about 1-2" around the edge?
thanks
G:confused:
Try larger… 6 inch flange is better. Like someone else said in another thread, " if you don’t need 6" flange, just trim it down later." a 2" flange won’t allow you the needed room if you decide to infuse with the mold. The tape you can say takes up 1" of flange itself, then the spriral wrap, wrapped in peel ply takes up another 1.5 inches or so. You should take a look at Airtech’s resin flow strips that can be reused, resin won’t stick to them. They are long narrow channels that distrubute the infusion resin across a larger distance/area of the bonnet. Also since they are made of silicone rubber or something soft/flexible it won’t leave an impression in your finished bonnet. If you are infusing that is.
I use aluminum sheetmetal flashing that is thin and easy to work with. Tape it to the bonnet from the underside using aluminum foil tape. The tape i get from HomeDepot in the airduct isle, the flashing same store in the roofing isle. Any good hardware store should sell both. The flashing comes on a roll of 25ft.
Then use some modeling clay to fill in the tiny gap between the bonnet and the metal flange. Take your time with the clay work and get it as perfect as you can.
Best Wishes on your mold 
thanks fastrr, i understand fully now even without pics lol. ill get the tape and tape to the bonnet sides to give me a good few inchs all around.
yeah me too… now i got 5 stiches. be careful!
the less clay you need, the better. bear in mind that when u spread the carbon cloth inside, it must be easy to conform to those curves otherwise you might get bubbles (or bridging as they call it)
You can lay single layers of CSM on a waxed glass panel, this gives you very flexible glossy strips to flange with. A large single sheet of masonite would also work here depending on the shape of the bonnet.
yes sheetmetal will cut you if your not careful. I’ve worked with sheetmetal alot in past jobs so i know to not grab the edges or slide your hand over the material.
Thin sheet aluminum is probably your best option. It’s easy to cut and shape, and requires little release agent application.
However, it’s very important to secure it well to the edges of the master part. It shouldn’t really flex when you’re laying up the mold.
Another tip, is to make the gaps as small as possible and fill them with non-drying clay. The clay should be very smooth to give a good finish on the perimeter of the mold and parts made from it. Take your time heating it up a little and smoothing it out with tools.