Jansling,
I've spent the better part of this afternoon trying to make an eccentric cone myself, and through my labors I've found a relatively simple method. I'm currently using Inventor 2013, and here's how I made mine:
In a Sheet Metal Drawing...
1. Create a sketch on any plane. Draw whatever diameter you need to be the bottom of your cone (Mine was 12").
2. After drawing your circle, draw a rectangle originating from the centerpoint of your circle. Make the rectangle's width 1/8" (.125") or whatever size of a gap you'd like between the ends of the plate. Extend this rectangle until it overlaps one side of your circle. Trim the circle laying inside the rectangle.
3. Exit Sketch.
4. Select 'Offset Plane' under 'Plane' and offset a plane to whatever height you need your cone to be (Mine was 108").
5. Create a sketch on your offset plane. Draw whatever diameter you need to be the top of your cone (Mine was 84").
6. After drawing your circle, draw a rectangle originating from the centerpoint of your circle. Make the rectangle's width 1/8" (.125") or whatever size of a gap you'd like between the ends of the plate. Extend this rectangle until it overlaps one side of your circle. Trim the circle laying inside the rectangle.
7. Exit Sketch.
8. Select the 'Loft' command, then select the second arc you created. After selecting the second arc, select the first arc you created. Under 'Output' (bottom middle of the window), select 'Surface'.
9. Click 'OK' to finish the 'Loft' command.
10. Under the '3D Model' Tab, select the 'Thicken' command. The 'Thicken' command will be on the right side of your Ribbon (if you are using the default Ribbon setup).
11. After selecting 'Thicken', specify the thickness of your material (right side of the window) and which direction you would like the material to go (left side of window, three buttons).
12. Under the 'Sheet Metal' Tab, select 'Flat Pattern', on the far right side of your Ribbon.
Voila! I hope that this helped out! I've also attatched my model to this post, if you run into any problems.
Can't find what you're looking for? Ask the community or share your knowledge.