should be above the sand. leave enough room between the two parts for a 3/4" pipe that will create the fill tunnel.
before you start the top half of the mold coat the bottom half with baby powder, to help with separation of the two halves. next place the top half of the mold box in place and begin filling and packing with sand. now you can loosen up and remove the pipe.
finally, you need to carefully separate the two halves. if you're successful, then remove the original plastic knuckles from the bottom half of the mold, being careful not to collapse the sand or disturb the axle. the steel axle 