Taper: The difference in diameter of top and bottom of a part. It gives slanting wall to the part. It is measured in terms of length.
Draft: The degree of taper of a side wall or the angle of clearance designed to facilitate removal of parts from a mold. It is measured in terms of angle.
· Taper or draft is almost required to assure easy removal of the part from the mold because the material will tend to shrink on the core of the mold and also the sticking can take place on both corer and cavity of the mold.
· A minimum draft of 1/20 and a maximum of 30 (if possible) on both the surface of the part is usually recommended.
· If the knockout pins are provided in the cavity section of the mold then the part should stick to the cavity and not to the core (plunger) hence the cavity is designed with no draft, the draft is only provided on the core.
· If the knockout pins are provided in the core section of the mold then the part should stick to the core and not to the cavity hence the core is designed with no draft, the draft is only provided on the cavity walls.
· Pick up ribs are also sometimes molded on the part to assure that the part will stay in the cavity or on the plunger.