Hi,
I`m making a dash board and the case mould has been made up of 10mm ali laser cut, then arranged to build up a 3d mould using 12mm bolts.

I have made up a case using normal resin (polyester?).
I left it for 3-4 hours before removing from the mould. The problem i have is the case is concave by 3mm on the long thin sections of the case.

I`m going to get a mould made up from the case to allow many to be produced, so i require a perfect case (buck
) to start with.
Would leaving it in the mould longer reduce the distortion?
I have thought about using polyurathane or epoxy instead. Is there any resins designed to have no shrinkage?

Thanks
Darren

The longer it's left to cure in the mould the better the product will be as fibreglass is a weird old fruit and will move all over the place.

Mark

Is it pure resin you're using? When ever I've done casting work I've added a filler. Usually a chalk based very very fine powder, but other bulk fillers are available. The filler really helps reduce shrinkage, because no matter how long you leave pure resin it WILL contract.

Thanks for your replies.
Been using chopped strands, for one, tring pure resing for next as the last one one had air trapped on surface.
Goos idea re filler, if it were 20% resin then only that could shrink.
I`ll try talc tomorow as a filler.
Thanks
Darren

Look for a polyester casting resin. General purpose GRP type polyester resin just shrinks too much.

It would help to use low catalyst levels (especially with the hot weather) and cure as slowly as possible. Whatever happens, it will shrink.

As has been said previously, you need to leave the item in the mould for three or four days, not hours, for it to fully cure. If you are making the master copy, and then intend to make a mould of that so you can cast a few/many, then you will need to leave the item for a couple of weeks, to allow all of the resin to harden completely, otherwise when you try to pull a mould from it both items will stick together, (regardless of using a release agent). If you want your buck to remain nice and flat, you can add some reinforcing on the reverse side, thin strips of wood, etc, and put your chopped strand, pre wetted out, over them. HTH Ray