Well, the problem is that you put the hole into a sheet metal part, so solid works creates a hole that will most closely approximate the desired round opening in the cone, but knowing that the shape will be punched into flat sheet metal. Conversely, if you punch a round hole in thick sheet metal and THEN form it into a cone, you will NOT have a round opening.
The trick here is to decide if you want a round opening (fitting a shaft?) or need to use a round punch in the flat pattern. If you are going to machine (drill,etc.) the hole round, then make the model first as a solid cone part (loft along a center line between two concentric circles) then SHELL the part to the desired thickness, and then cut in half. After that you can drill your hole.
I am afraid that if you want a round hole in the side of your cone you will need the "egg-shaped" punch in the flat pattern. Your egg will look a little nicer if you put the hole on a radial line also, not off-center as it is now. It might be easier to grind the punch also! Better yet, take the geometry from SolidWorks and EDM a punch from tool steel!
how do you calculate the form of this egg shaped of the flat pattern?
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