The size and shape limitations depend heavily on the machine being used. On most lathes there is an outer diameter limit of 8" and a length limit of 42". Parts any bigger can not be made on the lathes in the machine shop. The shape of the parts made on a lathe must be radially symmetric. Since the lathe spins the part while taking material off of the radius, no shapes other than those with a circular cross section can be made.