Design Tip -12

After some days without design tips. Here you are a new tip to avoid/minimize the sink marks on the screwing towers.
This tip is very easy to apply at the beginning of the design but it has a higher cost if it is applied after the mold finish.
So my suggestion is to apply it to the design and only remove it if it created some flow lines. Sometimes it can create flow lines that could be critical for not painted and visible parts, for chrome plated parts and also for very thin paints. On parts with regular paints or parts with primer the flow lines won't be visible.
The tip consists on increase a little bit the recess of the central hole. This design reduces the "ball" that creates the sink marks. It is important to not to make the recess too big in order to avoid flow line problems. There is not a magic number for this dimension. On my applications (small parts with thickness around 2 mm) I use recesses from 0.4 mm to 0.8 mm. 
This won't be the only tip about the screw towers, it is a feature quite difficult to design. .