Several machines have been devised to help the grower. There will normally be some sorting error in machines because of variations in dimension and shape. Oysters may also have grown together if they were piled in a corner of the tray and left unattended for too long. These usually consist of two layers that shift rapidly back and forth along a single plane of motion. These layers are screened with specifically sized mesh screens.
Larger animals remain on top while smaller sizes fall to the layer below.
The smaller screen size in this level, also shaking rapidly back and forth, will split the individuals again into larger and smaller individuals. Although it may appear to be rough for the animals, there is no significant increase in mortality as a result of this process. This type of grader is very effective for handling large amounts of seed and small oysters and clams. Rotary Graders Rotary graders are generally simple but effective devices for handling reasonably large quantities of stock. Most of the ones in use by growers have been constructed from materials that once had other functions.