Trying Something Different And It Went Horribly Wrong

Описание: Instead of joining a front and back half and sanding away the line, or making a one piece mold with no line, I am trying a completely different approach to making the spherical speaker enclosures.

It has now been decided that the speaker will be a three and a half way, meaning that each speaker will require four spherical enclosures, or eight for a stereo pair. With this in mind, I decided to make one mold for the front halves of all four spheres and another mold for all four back halves. We get all the sonic goodness of spheres without the problems associated with hiding where front and back are joined and without the need to join all four together afterwards. Its just a front half and a back half, and that's it. Easy.

And I made some dumb beginner mistakes. I did not get cure inhibition, so that went well, but I needed a lot more layers of silicone on the vertical parts. I am also starting to think there should be key features everywhere to really lock the soft silicone liner into the hard fiberglass shell.

With the side walls of silicone being so thin, it revealed what may have been some of the problems with the one piece molds. The thin side wall of the silicone liner allowed wrinkles to form in it. I was able to coax most of the wrinkles out before starting to paint gelcoat into the mold. The more time I spent brushing gelcoat on, the larger the wrinkles got until they were cartoonishly large. I am wondering if this is related to my problem with the one piece molds where castings were never really smooth spheres, but had gently rolling hills all over the sphere. It was subtle, but noticeable.

I have three ideas about how this might work;

1, solvents in the gelcoat makes the silicone swell. It is possible to make slightly larger parts if you soak a silicone mold in mineral oil. It soaks into the silicone and swells the mold in a surprisingly even manner.

2, Solvents permeated through the silicone and added vapor pressure inside the small stuck-down wrinkles, inflating them.

3, Air from wrinkles I coaxed out was able to move back as I moved things around when applying the gelcoat.

Since two of the explanations involve unwanted reactions between silicone and the polyester resin I am using, I think I should try using some urethane resin that is known to be compatible with silicone in some sort of test.

To find out, I could try casting urethane into one of the sphere molds I know to be bad, just to see if the casting is less hilly. Alternatively, I could re-make this part knowing there will at least be the small wrinkles, but there won't be cartoonishly large wrinkles if my problem was with the gelcoat.

Moving forward, I think I'll make the back half of this four way, using a lot more layers of silicone. I should use some thickener to get the vertical sides built up thick enough, and use a lot more key features, especially on the vertical sides where they should be most effective in locking the silicone liner into the hard shell.