Mold construction help

[watchtherocks]

Not exactly a boat I know, but I am attempting to construct a mold for an underwater camera housing. The problem I'm having is getting a smooth interface between the bottom edge of the mold and the metal plate I am using to get the edge straight. The curve has to go down right to the plate, but there are gaps of up to 3mm-ish that I can't reduce due to the internal construction of the mold. Given it would be possible but hard to do this with the mold attatched to the plate - it is not - are there any fillers or techniques that could help here?

[jiggerpro]

Maybe a bed a of epoxy mixed with some microballoons against which while soft you can push the piece to get the epoxy paste squeeze out and fill your gap.

[SamSam]

Or attach some sandpaper to the plate and slide the housing back and forth to easily sand the edge flat.

Or layup the housing and then while still wet lay a flat plate, waxed with release, on top and leave until cured.

[shoe]

You can use modeling clay to fill the gap, then shape with sculpting tools. This will also help hold the housing to the plate.

[watchtherocks]

Apologies for my absence.
I think SamSams second suggestion to layup the gap and then set it on the plate is a good idea, however given I need to get a really nice transition would adding filler to the mix help with shaping and sanding? Also would just a couple layers of wax be good enough for the aluminium plate? The stuff doesnt exactly rub into it well.

My design is a vac-bagged 2 layer-filler-2 layer sandwich construction. I'm planning to use a surfboard filler called Q-cell. This is not generally used structurally, but I made a non vac-bagged single layer layup, which is unbendable on the curves (most of it) and gives slightly where flat. A 1/8cm(ish) layer of q-cell/resin mix made it unbendable. This layup would be both very light and very strong, Im hoping. There are probably better ways of doing it, but given this is my first time using composites starting simply seems my best bet.
Also, do you normally apply a gelcoat to both the inside and outside of a layup?
Cheers guys.

[watchtherocks]

Would anyone like to contribute?

[SamSam]

Wax up the backside of the plate and try a test patch, it should be alright. As shoe said, modeling clay will fill the gap, then the whole plug waxed a number of times and then a layer of PVA.

Gelcoat inside isn't needed but makes it look good.

[watchtherocks]

Ive only got non-hardening model clay, I suspect this won't work?

[Herman]

This will work, no problem.

All clay we use is non-hardening, and even can be reused. It gets softer with heat (knead it for a couple of minutes with your hand to make it workable) then when it cools again it becomes harder, but never rock solid.