Somehow I did it the first time, but the attached file is giving me trouble. Very annoying. Cannot make the thin extrusion thing go away consistently. I "attached" (anchor icon) the second extrusion's sketch, and it seemed to work, because it was magically solid. I am trying to do the same with the third sketch, I "attached" them but it just won't let me NOT make a thin extrusion.
So what do I need to know?
Close the sketch by converting the circular edge & trimming back to the straight lines.
Aha. I actually ended up using a three-point arc, but same thing.
New question. I want to do a dimension from the middle of the big hole to the edge of the part. Or anything else like it. But I cannot make "smart" dimension do so any which way, in 3D. The length of any of the edges of extrude 4 is off limits for reasons unknown. How can I make that work?
Close the sketch by converting the circular edge & trimming back to the straight lines.