Hi there, I am having some issues trying to draw a rib feature on my model. I can draw the rib with a 2mm thickness, but I need it to be 1.5mm, However reducing the size is casuing the zero thickness geometry error. Anyone have any ideas? I have attatched an image of the problem,

PS drawing the lines attached to the model does not help either, I know this will be something silly that I am overlooking!

(the sketch lines are where I want the rib to be, the middle rib is OK)

Thanks.