Rib Design

There are some general guidelines for designing ribs in plastic parts. Figure 1 shows some common dimensions for a rib, where w is the wall thickness.

The thickness of the rib depends on the functionality of the part, and the material. If sinks opposite the rib are not a concern, the rib's thickness should be w. If sinks are a concern, 0.5w should be used for high shrink materials like polypropylene and polyethylene. 0.75w should be used for low shrink plastics like ABS and polycarbonate.

Rib spacing is a concern because of the mold's ability to properly cool the part. There should be a minimum of 2w between ribs.