Our first mould was made from an entire fingerboard, lifted off a guitar neck. It was complete, including frets. It was also a peculiar size - not quite 25.5" scale length, with a massive 24 frets, and a super-skinny nut width of just 41mm.
Our kit guitar has a 25.5" scale length neck, 21 frets, 46mm across the nut and 54mm at the 21st fret. A pretty "standard" fingerboard layout. So we made a "blank" of the fingerboard out of mdf, with slots to accept the fret wires, radius-ed it to 13.5" (using a home-made sanding block) and prepared it for silicone casting.
To help reduce the amount of silicone needed (it's pretty expensive stuff!) this time we made the box a bit tighter around our blank.
And because there's always a little bit of silicone left over when doing these kind of jobs, we stuck a couple of "Blood Bowl" miniatures into some Play-Doh to have a go at two-part resin casting. Blood Bowl miniatures are quite expensive on eBay, so we might get away with casting a couple of the ones we'd previously bought, just to bulk out a few teams (that's right, we've not given up on the electronic board game idea - just working on a couple of other things alongside it at the minute!)
(a glass bowl is great for mixing the silicone rubber - once we've scraped out as much as we can, simply leave it to cure, then peel the excess/waste away from the glass in the morning!)
The silicone is now mixed and poured and we're just going to leave it overnight to ensure it's cured fully before turning out the moulds.