Mold back draft

A method of producing two-color pieces in thermoplastic materials by successive injection molding operations. A taper or slope in a mold that facilitates removal of the molded piece. The opposite of this is called back draft, q.v. 

Back draft (back taper, counterdraft) n. A slight undercut or tapered area in a mold tending to prevent removal of the molded part. Complete textile glossary. Celanese acetate EEC, New York, 2000. 

Draft n A slight taper in a mold wall, proceeding inward from the parting surface to the bottom of the cavity, designed to facilitate removal of the molded object from the mold. When the taper is reversed, tending to impede removal of the article, the term back draft, or reverse draft is employed. In weaving, a pattern or plan for drawing-in. 

The draft specification controls the way the mold is built as the direction of draft normally indicates the direction of draw (removal of the part from the tool) since reverse draft would be an undercut condition. For injection molding, the mold designer will attempt to locate the core on the back, or movable, half of the mold. That is the side where the molding machine s ejector bars are located, and locating the core on that half makes the ejector mechanism available to push the part off the core. Part designs with cores from both sides of the part may require slight undercuts to keep them on the side of the mold which has the ejector mechanism. The draft specification will also control the location of the parting line, which should be indicated. 

---