Avoid deep & thin ribs if possible
Deep ribs require draft and clearance in order to allow the milling tool access. The maximum tool lengths average between 8-12 times the tool diameter.
Also worth noting is that deep, thin ribs tend to increase the mould milling time and make hand polishing difficult and time consuming.
Sometimes deep, thin ribs may result in potential collisions and/or geometry issues at the bottom of the mould cavities.
Final part shape can be affected when this occurs.