I have been avoiding doing a split mold due to me trying to wrap my head around some things. I made a crappy picture in paint to help me explain a bit. I am sure I am over thinking these things and when I do my research about it, I just overlooked or misunderstood something. I am thinking about making a mold of my tank on my chopper. I would have to split the tank down the middle lengthwise due to a reverse curve that would lock the mold otherwise. So when you make the 2 parts you make the divider out of metal or plastic or whatever you use, you then us filleting wax or modeling clay to fill the gap between the part and the split flange. I know that you try to use just enough wax to fill any gaps and all, but no matter how hard you try I feel like this will make a small curvature to the mold. So if you do this for both side that you now have a small upside down v where the 2 halves meet. When making the part and you bolt the 2 halves together, do you fill the gap between the halves with wax and if so how to you make sure it is flat and wont transfer to the part?

When you do a split mold put the center divider on, lay your fabric and resin against this, then allow it to fully cure. Next remove the divider material (it helps placing th edivider in a way that is sturdy enough for lay up against it but not so overkill that it can't easily be removed) and place what ever release agent on the newly cured upright segment of the splitter. Next you can just continue making your mold on the other half of the plug since the upright portion is already there. This will minimize any V gap as you mentioned. Even if there is a bit of curvature with the filet wax, when you start lying the other side it will be filled and will eliminate the problem you describe. You might want to add some key into the center divider portion so that they will mate properly when you reassemble the halves of the mold for use. These keyed sections should be built into/added onto the center divider at the outset before you start laying your reinforcement on the first half.