In the design of injection molded parts, sharp edges and corners should always be avoided. This is because they lead to the following results:
Instead, by applying radii and fillets, the following results can be achieved:
Radius and fillet dimensioning
Figure 1 - Corner radius.
Figure 2 - Stress concentration as a function of wall thickness and corner radius.
Like a radius or fillet, a chamfer can be used to soften sharp edges or make a gradual transition between two perpendicular faces. In view of minimizing stress concentration and optimizing flow, a radius is better than a chamfer. However, a chamfer can offer additional functionality like facilitating manual positioning of parts during assembly. A chamfer can also be used from an aesthetics point of view: where many parts are rounded-off, a chamfered edge creates a distinctive look. As with radii, a uniform wall thickness is preferred, so a chamfer on an outer edge should be copied on the inner corner.