The bowl sites at the bottom of the machine, so that all of the ball bearings roll back towards the wheel. I measured the space left over between the wheel and the front of the machine, this is the size of the bowl. Make sure that you mark a notch in the right hand side for the wheel cover, I forgot to do this, fortunately cutting it after carving didn't cause a problem. I carved the bowl using a 12mm Veiner to get the shape and a small almost flat gouge to smooth it out. Finally I sanded it smooth. It took me two tries to get this right, as the bowl needs to sit slightly above the holes in the wheel, so that the ball bearings just roll into them.