mold insert to deal with negative return corners??

[Pavook]

Hi,
I need help with a small problem.
I have a situation where the mold I need to build will have a negative return/corner in it. (see attached sketch). For various reasons I cannot do a split mold, or a two piece part.
Is it possible to incorporate an insert into the mold to deal with this? See the lower sketch to see what I mean. First mold and the insert are properly covered with mold release agents then the insert is placed on the mold (perhaps with super 77?). Then the part is laid up. When cured, the part is de-molded with the insert still embedded in the laminate, then I simply remove the insert, and I have exactly the part I want.
Can this be done? Will it work?
Your help is appreciated.

[grp.boat]

Thats the way to do it. I do exactly the same with a recess for the battery switch on one of my mouldings. I screw it to the mould from behind, then radius the gap with plasticene to seal the joint before gelling.

steve

[Pavook]

Thanks Steve,
so the plasticene doens't inhibit de-moulding?
do you think it would work on a large mold? lets say the insert was 6 ' by 1'?
and do you think this technique would workin vacuum baggin or in resin infusion?
cheers

[DGreenwood]

I do the same thing with Fillet wax. Composites One sells it and the tools to put it in. I have never been able to do such a perfect job so that there is no Gelcoat touch up after pulling. It works fine with vacuum bagging. Obviously with the wax, heat is an issue so temp cured prepreg is no good.
I make inserts that big out of Starboard and it works fine. The wax does not interfere with release.

[rxcomposite]

Originally Posted by Pavook

Thanks Steve,
so the plasticene doens't inhibit de-moulding?
do you think it would work on a large mold? lets say the insert was 6 ' by 1'?
and do you think this technique would workin vacuum baggin or in resin infusion?
cheers

I did this once with vacuum bagging. I used melted wax to temporary hold the insert in place. Just strong enough to stay in place but would release at a tap of a hammer. I used modeling clay to seal/round off the edges of the insert. works fine. Made 17 parts out of the technique.