Draft, Ribs, and Bosses in Plastic Parts

Three features make or break a plastic part. Get them right and the part molds cleanly and releases every time.

• Draft — 1 to 2 degrees on vertical walls so the part releases
• Ribs — add stiffness without thickening walls (keep rib thickness around 60% of the wall)
• Bosses — for screws; keep them short and core them out to avoid sink

The common mistake: thickening a wall for stiffness. Thick walls cool slowly and sink. Ribs give the same stiffness with even walls — and a part that actually releases from the mold.