VOIDS AND SHRINKAGE
Troublesome shrinkage problems can be caused by the intersection of walls that are not uniform in wall thickness. Examples might include ribs, bosses, or any other projection of the nominal wall. Since thicker walls solidify slower, the area they are attached to at the nominal wall will shrink as the projection shrinks. This can result in a sunken area in the nominal wall. Such shrinkage can be minimized if a rib thickness is maintained to between 50 and 60 percent of the walls they are attached to. To further our example, bosses located into a corner will produce very thick walls, causing sink, unless isolated as in the illustration below.