How to draft plastic parts
Adding draft to plastic parts is more difficult than it seems. It is an area which plastic part designers rarely get right.
As you see in the picture at right, the draft angle must slope away in the direction of pull. That is the direction the part will come out of the mold. If the parting line splits a surface, the draft must split there as well.
When the parting line has to go up or down on the part, to meet some feature, it is ideal to go gradually. Gradual slopes can be drafted in such a way as to prevent mismatch on the two sides of the mold, as seen in the turquoise part at right.
The purple part at right shows a steep parting line step to meet a feature. Notice that it shows a mismatch area. This mismatch could be eliminated, but the part might not look as good. Also note that the parting line does not follow every feature. It is best to keep the parting line as simple as possible. Every jog adds cost to the mold as well as reliability issues.