I've made a lot of mold in my time. I recommend RTV silicone rubber for the mold.
Place wheel on a piece of flat wood, no sides yet.
Use any kind of non-sulfer based clay, and clay up one half of mold. This will take you a long time. Use very small tools to get into every nook and crevis. You want not to have any undercuts. Try hard to have 90 degree side to every surface going to the wood base. ( I hope I'm making sense ).
Hot glue your walls up around the wood base.
Mix up RTV silicone and evacuate it for about 10 minutes. Pour slowly into mold. You might want to made sure it gets into every nook and cranny, use a toothpick, but don't scerw up the clay around your object.
Wait a day for the RTV to cure.
Remove only the wood base from the side of your mold. NOT the sides. Do not remove those. The wood base should pull away from the RTV with no problem and the part should be stuck into the RTV holding it in.
Start removing every bit of clay from the part and RTV. Clean it well.
Spray a mold release onto your mold. If you don't care about the original just paint it with any color spray paint like Krylon. I ususally use Semi Flat Black. It dries fast and you can see the area where you cover the RTV. Some Mold releases are transparent and you continue to spray too thick a coat. That's why I use an opaque paint.
Glue on sides to your mold and repour another half.
Wait another day and then demold.
Cut out your pouring spouts and vents and your done.
Rick
