Sepor’s batch ball and rod mills are designed to give size reduction of laboratory quantities of minerals and ores. Feed size should generally be -1/8″, for ball mill and -1/2″ for rod mill. They are of a sturdy, rugged design to handle frequent use with hard materials. The batch ball and rod mills require a drive roll to rotate the mill the proper grinding speed, usually 60%- 75% of the critical speed for ball mills and 50% to 90% of critical speed for rod mills.