Glass Top Case With Pullout Tray — Black Pulley and performs well on many Size:6 mm and performs well on many surfaces For optimum action the barrel should be used approximately two thirds full of combined media and stones or parts If it is overfilled there will be very little tumbling action and if underfilled there will be slippage of material without any abrasive action Your stones or parts should be sorted for compatible size shape and hardness to ensure uniform sanding and polishing Tumbling is an art and a science and will require experimentation and practice to perfect your recipes for various materials There are many different tumbling machines and supplies available to adjust your techniques and equipment to the stones at hand