I'm designing a very large injection molded cover for a piece of industrial equipment. 58 pound shot, over two feet tall. This cover needs ribs on the inside top and side walls. We don't want to use internal action.
Vertical ribs will work, but there is a draft problem. Obviously I can't just draft the ribs relative to the parting line because they'll get too thick at the top. So I'll draft them relative to the side walls, which are inclined between 5 and 10 degrees. The draft on the side walls vary because they are curved.
This will work because a rib drafted relative to the surface it adjoins is drafted relative to the parting direction if that surface is inclined.
What I've done is create a rib that is .200" at its thickest and .080" at its thinnest and using a variable section sweep referencing the parting plane, I'm letting the rib depth float so it maintains 1/2 degree of draft relative to draw.
This works great going up the side of the wall. As the wall curves over, the ribs get deeper to maintain 1/2 deg draft, which is what I want.
My problem is, I want the ribs on the side and the roof to be the same rib, but there is nothing preventing the rib depth from approaching infinity as the rib approaches horizontal on the top.
My question is this: Is there a way to write a relation where the rib depth (which is being driven by the draft requirement) will limit to 1" and therefore change from 1/2 degree draft to whatever it wants to be as the rib rounds the corner from the side walls to the roof?
Does this question make sense?
Thanks,