I really like this approach. We may have a winner! The beauty of this approach is that I am able to do a "blend" feature while creating a mold volume in Creo/Mold.
I could offset the first section with a relations over a given distance to create a nominal draft angle.
I will investigate this further.
I really thought we (you) were on to something here. I'm not sure if this is an issue yet, but the resulting surface is not a true cylindrical surface. I'm not sure why, but you are unable to add an axis through the resulting "round". Like I said, I'm not sure it's an issue yet.
The EDM probe can take on any shape you want if you are using a plunge EDM.
If you are wire EDM'ng this, then you have to decide on what is moving to get the noted draft.
So there is little limitation but if this draft if for molding, typically you would make the straight part and add draft afterward.
Doing this makes for more uniform drafts which are easier to machine (taper bit, single axis and all that).
In this vein, I find it very hard to match drafts with simple resulting rounds since their taper angle is not controllable in the Round feature dialog.
I think you are looking for a "full round" feature for this. You would add your 3rd (intermediate/depth) surface in one of many ways.
As I mentioned, the only straight line on a cone is one that passes through the vertex. And the only cylindrical fillet that can be tangent to a cone has to be tangent along that straight line, so it cannot also be angled to follow tapered blocks.
My guess it that the blend isn't a true cone, which allows what looks like a cylinder, but is an elliptical section normal to the slope.
Fortunately I already know enough about wire edm. What I don't know is why the design is caught between geometry reality and a machining method that can't produce that geometry. One or the other needs to change.
This is what you get when you add draft after the fact. What most machinist would want generically.
In this case, you are assured constant draft if both features have the same draft.
Surface tangency is maintained (missing element in sweep methods).
note: transition lines for round-to-cone project to the cone's center.
...and sweep feature in combination of fills and boundary blends merged into a solid.
The challenge with the toolbox we have is to know when the surface is curved from normal.
Features such as Blend and Boundary Blend (top to bottom) is the way the connections are parced.
Even using sweep, you have to be sure to choose constant normal.