The coils were wound from 1.6mm enamelled copper wire. Each coil was left clamped in the cheek-pieces until the incorporated high-temperature silicon had set. Each coil had a wooden core that was left in place too, to screw it in place in the stator mould.
The coils all stay completely compact and tight when handled. I think it can only help performance to keep the coils tight. Heat should dissipate more quickly to the outside if the copper is densely packed and not filled with resin which is a poor conductor. The silicon is rated to 300 degrees celcius so it shouldn’t melt or bubble inside the stator. It holds the wires together yet you can peel it away easily to make a better surface for the stator material to key into.
My coil winder is held in a bench vice making it very solid, I cut it from a piece of scrap douglas fir. I used scrap melamine/formica coated chipboard for the cheek-pieces and my moulds. It’s very flat and stable and sticky stuff releases easily from its surface.