When mass finishing—finishing many parts simultaneously—in a vibratory finishing system, the tendency is to use ceramic or plastic preformed cutting media, said Steven Schneider, technical sales manager at surface finishing company Kramer Industries Inc., Piscataway, N.J. Ceramic tumbling media are made with abrasive filler, much like a grinding wheel. For plastic tumbling media, plastic is mixed with abrasive filler and cast to shape. Ceramic media use aluminum oxide as filler, and plastic media use quartz or silica for cleaner results.

"Randomly shaped media, either man-made or natural, are rarely used for precision work because they tend to jam in the holes and do not deburr into corners or recessed areas," Schneider said. "When using ceramic media, care should be taken to avoid glazing or loading of the surface. It is a good practice to run the media with an abrasive grain occasionally to roughen the surface and clean the pores."

The DB300 vibratory tumbler by Kramer Industries. DB tub vibrators are designed as starter machines for novices or shops on a limited budget.

Plastic tumbling media are self-cleaning due to their relatively soft bond, he said. Because adding abrasive filler to plastic media materially reduces the life of the substance, this media should be used only for mild cutting jobs that do not require adding abrasive filler.

"Plastic tumbling media are used mainly for fragile parts or soft metals," he said. "Because plastic tumbling media weigh significantly less than stone or ceramic tumbling media, plastic is safer to use in such cases."

There is much more to mass finishing than the selection of cutting media. For information about part details, processing speeds and costs, read "Starting Mass Finishing" in the current issue of Cutting Tool Engineering.