The number of parts that can be tumbled (vibratory or barrel) will depend on the dimensions of the part and the desired final finish. Lower ratios of media to parts (no media, 1:1 or 2:1) will lead to rougher finishes and can be used on castings and forgings for aggressive deburring. Moderate and the most common ratios (3:1, 4:1 or 5:1) will minimize part to part interaction and are ideal for moderate deburring and surface finishing. High ratios (6:1, 7:1 and higher) are used for pre-plate and decorative finishes or for fragile parts

The quantity of parts that can be processed in a given system can be determined by first calculating the ‘box’ size of the part (basically width x length x height). Given the known volume of the tumbler being used (50% for barrels and 90% for vibes, typically) and the box volume of the part, the quantity of parts and media can be calculated for any ratio.

For example, let’s assume a 3 cubic foot vibe and a part size of 2″ x 3″ x 4″ (box = 24 cubic inches) and a media to parts ratio of 3 to 1. With the vibe 90% full, the total usable capacity is 2.7 ft3. At a ratio of 3:1, 25% or 0.675 ft3 (1,166 in3) of the usuable capacity will be parts. With the size part noted, the process will be able to tumble about 48 parts per batch (=1166/24). The balance of the capacity (2.025 ft3) will be tumbling media.