TERRIBLE wheels can be made by cutting a circle of plywood, screwing bike tread round the outside, drilling an 8mm hole through te centre and putting an m8 bolt through the hole and a nut and washer in the other side, do this up as tight as physically possible. You can then hold the shank of the m8 bolt in the chuck of the drill and potentially once the chuck is tightened drill a small hole all the way though the chuck and bolt and put a small bolt/pin though to stop it loosening.

A better solution is to make wheels as shown in Ellis' guide in the media section of the forum.