I've been rubbish at posting here recently. my bad.
Time for some rubber.
First, Thomas needed a seam line. I got the positioning of the seam using a fine piece of thread, when pulled tight it gave a perfect straight line. This was then marked on the dome. I then positioned 2 pieces of tape along the line with a 1mm gap between them. I then used a fine tooth saw to cut into the dome, just about a 1mm though, the same as the height of the saw teeth.
Then it was on to wet sanding, starting with about a 24o grit, working my way down to a 1200. Once sanded, a clay dam was placed around the dome, to split the silicone. I reckon I could have got away with a 1 part mold, but chickened out at the last minute. Only had enough silicone in stock to do it once (plus, i didn't fancy wasting it either)
Liberal coating of mold release then its on with the silicone. Smooth On Rebound 25, as usual. Thinned down layer to start then several layers at normal viscosity. Thena thickened layer to build up a ridge around the seam and to attach the registration key.
Once it set, the clay dam is removed and all the clay carefully cleaned away from the silicone. You can see the registration keys that were imprinted into the clay are now part of the mold. It is important that the silicone is properly coated with a barrier so that the 2nd part to the mold doesn't bond to the first half. I used a paint brush and some petroleum jelly, then some mold release aerosol.
Then its on with the second half of the silicone, same as before.
The hard outer is made from Smooth On Plasti-Paste II, with an 3 piece MDF frame held together with some bolts and wing nuts for easy opening/closing. I attached pieces of foam core to the bottom of the piece. this was to give me a level to work to with the plasti paste and to avoid any sharp edges.
