Dec 30, i would suggest that you build a rod mill if you want to get the material down to a fine power, a ball mill usually is used to make bigger item smaller, e.g. big rocks down to little rocks, and then the material goes into a rod mills to take it down to a.Effect of ball size and properties on mill grinding capacity current ball milling theory suggests that grinding capacity is influenced by the size of balls charged to the mill. in selecting the appropriate ball charge, the first objective is to determine that ball size which will grind the coarse particles most efficiently. this size should be the largest ball size charged to the mill. the.